PLEASURES OF THE TELESCOPE

AN ILLUSTRATED GUIDE FOR AMATEUR ASTRONOMERS AND A POPULAR DESCRIPTION OF THE CHIEF WONDERS OF THE HEAVENS FOR GENERAL READERS

 BY GARRETT P. SERVISS

 AUTHOR OF ASTRONOMY WITH AN OPERA-GLASS

"This being made, He yearned for worlds to make From other chaos out beyond our night-- For to create is still God's prime delight. The large moon, all alone, sailed her dark lake, And the first tides were moving to her might;Then Darkness trembled, and began to quakeBig with the birth of stars, and when He spake A million worlds leapt into radiant light. "

 LLOYD MIFFLIN. 

 _WITH MANY ILLUSTRATIONS_

 NEW YORK D. APPLETON AND COMPANY 1901

 COPYRIGHT, 1901, BY D. APPLETON AND COMPANY. 

PREFACE

By the introduction of a complete series of star maps, drawn speciallyfor the use of the amateur and distributed through the body of the work, thus facilitating consultation, it is believed that this book makes astep in advance of its predecessors. The maps show all of the starsvisible to the naked eye in the regions of sky represented, and, inaddition, some stars that can only be seen with optical aid. The latterhave been placed in the maps as guide posts in the telescopic field toassist those who are searching for faint and inconspicuous objectsreferred to in the text. As the book was not written for those whopossess the equipment of an observatory, with telescopes driven byclockwork and provided with graduated circles, right ascensions anddeclinations are not given. All of the telescopic phenomena describedare, however, represented in the maps. Star clusters are indicated by aconventional symbol, and nebulæ by a little white circle; while a smallcross serves to mark the places where notable new stars have appeared. The relative magnitudes of the stars are approximately shown by thedimensions of their symbols in the maps, the smaller stars beingrepresented by white dots and the larger by star-shaped figures. 

In regard to binary stars, it should be remembered that, in many cases, their distances and angles of position change so rapidly that anystatement concerning them remains valid only for a few years at themost. There is also much confusion among the measurements announced bydifferent authorities. In general, the most recent measurementsobtainable in 1900 are given in the text, but the observer who wishes tostudy close and rapid binaries will do well to revise his informationabout them as frequently as possible. An excellent list of double starskept up to date, will be found in the annual Companion to theObservatory, published in London. 

In the lunar charts the plan of inserting the names of the principalformations has been preferred to that usually followed, of indicatingthem only by numbers, accompanied by a key list. Even in the mostdetailed charts of the moon only a part of what is visible withtelescopes can be shown, and the representation, at best, must be merelyapproximate. It is simply a question of what to include and what toomit; and in the present case the probable needs of the amateur observerhave governed the selection--readiness and convenience of referencebeing the chief aim. 

It should, perhaps, be said here that the various chapters composingthis book--like those of "Astronomy with an Opera-glass"--were, in theiroriginal form, with the single exception of Chapter IX, published inAppletons' Popular Science Monthly. The author, it is needless to say, was much gratified by the expressed wish of many readers that thesescattered papers should be revised and collected in a more permanentform. As bearing upon the general subject of the book, a chapter hasbeen added, at the end, treating on the question of the existence ofplanets among the stars. This also first appeared in the periodicalabove mentioned. 

In conclusion, the author wishes for his readers as great a pleasure inthe use of the telescope as he himself has enjoyed. 

G. P. S. 

BOROUGH OF BROOKLYN, NEW YORK, _January, 1901_. 

CONTENTS

CHAPTER I PAGE

THE SELECTION AND TESTING OF A GLASS 1

How to get a good telescope--Difference between reflectors andrefractors--How a telescope is made achromatic--The way to testa telescope on stars. 

CHAPTER II

IN THE STARRY HEAVENS 19

Orion and its wonders, Lepus, Canis Major, Argo, Monoceros, Canis Minor, and the Head of Hydra. 

CHAPTER III

FROM GEMINI TO LEO AND ROUND ABOUT 38

The zodiacal constellations Gemini, Cancer, and Leo, and theirneighbors Auriga, the Lynx, Hydra, Sextans, and Coma Berenices. 

CHAPTER IV

VIRGO AND HER NEIGHBORS 57

Crater and Corvus, Hydra, Virgo, the "Field of the Nebulæ, "Libra, Boötes, and the great Arcturus, Canes Venatici, andCorona Borealis. 

CHAPTER V

IN SUMMER STAR-LANDS 75

Scorpio and its red-green gem, Ophiuchus, Sagittarius, ScutumSobieskii, Capricornus, Serpens, Hercules, Draco, Aquila, andDelphinus. 

CHAPTER VI

FROM LYRA TO ERIDANUS 97

Lyra and its brilliant Vega, Cygnus, Vulpecula, Aquarius, Equuleus, Pegasus, Cetus, and Eridanus. 

CHAPTER VII

PISCES, ARIES, TAURUS, AND THE NORTHERN MARS 117

The first double star ever discovered, the Pleiades and theirphotographic wonders, the Royal Family of the Sky, Andromeda, Cassiopeia, Perseus and Cepheus, Ursa Major, Camelopardalus, Ursa Minor, and the Pole Star. 

CHAPTER VIII

SCENES ON THE PLANETS 139

Jupiter, its belts and its moons--Saturn, the ringedplanet--Saturn's moons and Roche's limit--Mars and its whitepolar caps and so-called seas and continents--Venus and heratmosphere--The peculiar rotations of Venus and Mercury. 

CHAPTER IX

THE MOUNTAINS AND PLAINS OF THE MOON AND THE SPECTACLES OF THESUN 156

Peculiarities of the lunar landscapes--The so-called seas, thecraters, the ring mountains, the inclosed plains, the mountainranges, Tycho's mysterious streaks, and other lunar featuresdescribed--How to view the sun and its spots. 

CHAPTER X

ARE THERE PLANETS AMONG THE STARS? 183

Significance of Dr. See's observations--Why our telescopes donot show planets circling around distant suns--Reasons forthinking that such planets may exist--The bearing of stellarevolution on the question. 

PLEASURES OF THE TELESCOPE

CHAPTER I

THE SELECTION AND TESTING OF A GLASS

 "O telescope, instrument of much knowledge, more precious than any scepter! Is not he who holds thee in his hand made king and lord of the works of God?"--JOHN KEPLER. 

If the pure and elevated pleasure to be derived from the possession anduse of a good telescope of three, four, five, or six inches aperturewere generally known, I am certain that no instrument of science wouldbe more commonly found in the homes of intelligent people. The writer, when a boy, discovered unexpected powers in a pocket telescope not morethan fourteen inches long when extended, and magnifying ten or twelvetimes. It became his dream, which was afterward realized, to possess amore powerful telescope, a real astronomical glass, with which he couldsee the beauties of the double stars, the craters of the moon, the spotson the sun, the belts and satellites of Jupiter, the rings of Saturn, the extraordinary shapes of the nebulæ, the crowds of stars in the MilkyWay, and the great stellar clusters. And now he would do what he can topersuade others, who perhaps are not aware how near at hand it lies, tolook for themselves into the wonder-world of the astronomers. 

There is only one way in which you can be sure of getting a goodtelescope. First, decide how large a glass you are to have, then go to amaker of established reputation, fix upon the price you are willing topay--remembering that good work is never cheap--and finally see that theinstrument furnished to you answers the proper tests for a telescope ofits size. There are telescopes and telescopes. Occasionally a rarecombination of perfect homogeneity in the material, complete harmonybetween the two kinds of glass of which the objective is composed, andlens surfaces whose curves are absolutely right, produces a telescopewhose owner would part with his last dollar sooner than with it. Suchtreasures of the lens-maker's art can not, perhaps, be commanded atwill, yet, they are turned out with increasing frequency, and the bestartists are generally able, at all times, to approximate so closely toperfection that any shortcoming may be disregarded. 

In what is said above I refer, of course, to the refracting telescope, which is the form of instrument that I should recommend to all amateursin preference to the reflector. But, before proceeding further, it maybe well to recall briefly the principal points of difference betweenthese two kinds of telescopes. The purpose of a telescope of eitherdescription is, first, to form an image of the object looked at byconcentrating at a focus the rays of light proceeding from that object. The refractor achieves this by means of a carefully shaped lens, calledthe object glass, or objective. The reflector, on the other hand, formsthe image at the focus of a concave mirror. 

[Illustration: IMAGE AT THE FOCUS OF A LENS. ]

A very pretty little experiment, which illustrates these two methods offorming an optical image, and, by way of corollary, exemplifies theessential difference between refracting and reflecting telescopes, maybe performed by any one who possesses a reading glass and a magnifyinghand mirror. In a room that is not too brightly illuminated pin a sheetof white paper on the wall opposite to a window that, by preference, should face the north, or away from the position of the sun. Takingfirst the reading glass, hold it between the window and the wallparallel to the sheet of paper, and a foot or more distant from thelatter. By moving it to and fro a little you will be able to find adistance, corresponding to the focal length of the lens, at which apicture of the window is formed on the paper. This picture, or image, will be upside down, because the rays of light cross at the focus. Bymoving the glass a little closer to the wall you will cause the pictureof the window to become indistinct, while a beautiful image of thehouses, trees, or other objects of the outdoor world beyond, will beformed upon the paper. We thus learn that the distance of the image fromthe lens varies with the distance of the object whose image is formed. In precisely a similar manner an image is formed at the focus of theobject glass of a refracting telescope. 

[Illustration: IMAGE AT THE FOCUS OF A CONCAVE MIRROR. ]

Take next your magnifying or concave mirror, and detaching the sheet ofpaper from the wall, hold it nearly in front of the mirror between thelatter and the window. When you have adjusted the distance to the focallength of the mirror, you will see an image of the window projected uponthe paper, and by varying the distance, as before, you will be able toproduce, at will, pictures of nearer or more remote objects. It is inthis way that images are formed at the focus of the mirror of areflecting telescope. 

Now, you will have observed that the chief apparent difference betweenthese two methods of forming an image of distant objects is that in thefirst case the rays of light, passing through the transparent lens, arebrought to a focus on the side opposite to that where the real objectis, while in the second case the rays, being reflected from thebrilliant surface of the opaque mirror, come to a focus on the same sideas that on which the object itself is. From this follows the moststriking difference in the method of using refracting and reflectingtelescopes. In the refractor the observer looks toward the object; inthe reflector he looks away from it. Sir William Herschel made his greatdiscoveries with his back to the sky. He used reflecting telescopes. This principle, again, can be readily illustrated by means of our simpleexperiment with a reading glass and a magnifying mirror. Hold thereading glass between the eye and a distant object with one hand, andwith the other hand place a smaller lens such as a pocket magnifier, near the eye, and in line with the reading glass. Move the two carefullyuntil they are at a distance apart equal to the sum of the focal lengthsof the lenses, and you will see a magnified image of the distant object. In other words, you have constructed a simple refracting telescope. Thentake the magnifying mirror, and, turning your back to the object to belooked at, use the small lens as before--that is to say, hold it betweenyour eye and the mirror, so that its distance from the latter is equalto the sum of the focal lengths of the mirror and the lens, and you willsee again a magnified image of the distant object. This time it is areflecting telescope that you hold in your hands. 

The magnification of the image reminds us of the second purpose which issubserved by a telescope. A telescope, whether refracting or reflecting, consists of two essential parts, the first being a lens, or a mirror, toform an image, and the second a microscope, called an eyepiece, tomagnify the image. The same eyepieces will serve for either thereflector or the refractor. But in order that the magnification may beeffective, and serve to reveal what could not be seen without it, theimage itself must be as nearly perfect as possible; this requires thatevery ray of light that forms the image shall be brought to a point inthe image precisely corresponding to that from which it emanates in thereal object. In reflectors this is effected by giving a parabolic formto the concave surface of the mirror. In refractors there is a twofolddifficulty to be overcome. In the first place, a lens with sphericalsurfaces does not bend all the rays that pass through it to a focus atprecisely the same distance. The rays that pass near the outer edge ofthe lens have a shorter focus than that of the rays which pass near thecenter of the lens; this is called spherical aberration. A similarphenomenon occurs with a concave mirror whose surface is spherical. Inthat case, as we have seen, the difficulty is overcome by giving themirror a parabolic instead of a spherical form. In an analogous way thespherical aberration of a lens can be corrected by altering its curves, but the second difficulty that arises with a lens is not so easilydisposed of: this is what is called chromatic aberration. It is due tothe fact that the rays belonging to different parts of the spectrumhave different degrees of refrangibility, or, in other words, that theycome to a focus at different distances from the lens; and this isindependent of the form of the lens. The blue rays come to a focusfirst, then the yellow, and finally the red. It results from thisscattering of the spectral rays along the axis of the lens that there isno single and exact focus where all meet, and that the image of a star, for instance, formed by an ordinary lens, even if the sphericalaberration has been corrected, appears blurred and discolored. There isno such difficulty with a mirror, because there is in that case norefraction of the light, and consequently no splitting up of theelements of the spectrum. 

In order to get around the obstacle formed by chromatic aberration it isnecessary to make the object glass of a refractor consist of two lenses, each composed of a different kind of glass. One of the most interestingfacts in the history of the telescope is that Sir Isaac Newton could seeno hope that chromatic aberration would be overcome, and accordinglyturned his attention to the improvement of the reflecting telescope anddevised a form of that instrument which still goes under his name. Andeven after Chester More Hall in 1729, and John Dollond in 1757, hadshown that chromatic aberration could be nearly eliminated by thecombination of a flint-glass lens with one of crown glass, WilliamHerschel, who began his observations in 1774, devoted his skill entirelyto the making of reflectors, seeing no prospect of much advance in thepower of refractors. 

A refracting telescope which has been freed from the effects ofchromatic aberration is called achromatic. The principle upon which itsconstruction depends is that by combining lenses of different dispersivepower the separation of the spectral colors in the image can becorrected while the convergence of the rays of light toward a focus isnot destroyed. Flint glass effects a greater dispersion than crown glassnearly in the ratio of three to two. The chromatic combination consistsof a convex lens of crown backed by a concave, or plano-concave, lens offlint. When these two lenses are made of focal lengths which aredirectly proportional to their dispersions, they give a practicallycolorless image at their common focus. The skill of the telescope-makerand the excellence of his work depend upon the selection of the glassesto be combined and his manipulation of the curves of the lenses. 

[Illustration: ACHROMATIC OBJECT GLASS. 

_a_, crown glass; _b_, flint glass. ]

Now, the reader may ask, "Since reflectors require no correction forcolor dispersion, while that correction is only approximately effectedby the combination of two kinds of lenses and two kinds of glass in arefractor, why is not the reflector preferable to the refractor?"

The answer is, that the refractor gives more light and betterdefinition. It is superior in the first respect because a lens transmitsmore light than a mirror reflects. Professor Young has remarked thatabout eighty-two per cent of the light reaches the eye in a goodrefractor, while "in a Newtonian reflector, in average condition, thepercentage seldom exceeds fifty per cent, and more frequently is lowerthan higher. " The superiority of the refractor in regard to definitionarises from the fact that any distortion at the surface of a mirroraffects the direction of a ray of light three times as much as the samedistortion would do at the surface of a lens. And this applies equallyboth to permanent errors of curvature and to temporary distortionsproduced by strains and by inequality of temperature. The perfectachromatism of a reflector is, of course, a great advantage, but thechromatic aberration of refractors is now so well corrected that theirinferiority in that respect may be disregarded. It must be admitted thatreflectors are cheaper and easier to make, but, on the other hand, theyrequire more care, and their mirrors frequently need resilvering, whilean object glass with reasonable care never gets seriously out of order, and will last for many a lifetime. 

Enough has now, perhaps, been said about the respective properties ofobject glasses and mirrors, but a word should be added concerningeyepieces. Without a good eyepiece the best telescope will not performwell. The simplest of all eyepieces is a single double-convex lens. Withsuch a lens the magnifying power of the telescope is measured by theratio of the focal length of the objective to that of the eye lens. Suppose the first is sixty inches and the latter half an inch; then themagnifying power will be a hundred and twenty diameters--i. E. , the diskof a planet, for instance, will be enlarged a hundred and twenty timesalong each diameter, and its area will be enlarged the square of ahundred and twenty, or fourteen thousand four hundred times. But inreckoning magnifying power, diameter, not area, is always considered. For practical use an eyepiece composed of an ordinary single lens isseldom advantageous, because good definition can only be obtained in thecenter of the field. Lenses made according to special formulæ, however, and called solid eyepieces, give excellent results, and for high powersare often to be preferred to any other. The eyepieces usually furnishedwith telescopes are, in their essential principles, compoundmicroscopes, and they are of two descriptions, "positive" and"negative. " The former generally goes under the name of its inventor, Ramsden, and the latter is named after great Dutch astronomer, Huygens. The Huygens eyepiece consists of two plano-convex lenses whose focallengths are in the ratio of three to one. The smaller lens is placednext to the eye. Both lenses have their convex surfaces toward theobject glass, and their distance apart is equal to half the sum of theirfocal lengths. In this kind of eyepiece the image is formed between thetwo lenses, and if the work is properly done such an eyepiece isachromatic. It is therefore generally preferred for mere seeingpurposes. In the Ramsden eyepiece two plano-convex lenses are also used, but they are of equal focal length, are placed at a distance apart equalto two thirds of the focal length of either, and have their convex sidesfacing one another. With such an eyepiece the image viewed is beyond thefarther or field lens instead of between the two lenses, and as thisfact renders it easier to adjust wires or lines for measuring purposesin the focus of the eyepiece, the Ramsden construction is used when amicrometer is to be employed. In order to ascertain the magnifying powerwhich an eyepiece gives when applied to a telescope it is necessary toknow the equivalent, or combined, focal length of the two lenses. Twosimple rules, easily remembered, supply the means of ascertaining this. The equivalent focal length of a negative or Huygens eyepiece is equalto half the focal length of the larger or field lens. The equivalentfocal length of a positive or Ramsden eyepiece is equal to three fourthsof the focal length of either of the lenses. Having ascertained theequivalent focal length of the eyepiece, it is only necessary to divideit into the focal length of the object glass (or mirror) in order toknow the magnifying power of your telescope when that particulareyepiece is in use. 

[Illustration: NEGATIVE EYEPIECE. ]

[Illustration: POSITIVE EYEPIECE. ]

A first-class object glass (or mirror) will bear a magnifying power ofone hundred to the inch of aperture when the air is in goodcondition--that is, if you are looking at stars. If you are viewing themoon, or a planet, better results will always be obtained with lowerpowers--say fifty to the inch at the most. And under ordinaryatmospheric conditions a power of from fifty to seventy-five to the inchis far better for stars than a higher power. With a five-inch telescopethat would mean from two hundred and fifty to three hundred andseventy-five diameters, and such powers should only be applied for thesake of separating very close double stars. As a general rule, thelowest power that will distinctly show what you desire to see gives thebest results. The experienced observer never uses as high powers as thebeginner does. The number of eyepieces purchased with a telescope shouldnever be less than three--a very low power--say ten to the inch; a veryhigh power, seventy-five or one hundred to the inch, for occasional use;and a medium power--say forty to the inch--for general use. If you canafford it, get a full battery of eyepieces--six or eight, or adozen--for experience shows that different objects require differentpowers in order to be best seen, and, moreover, a slight change of poweris frequently a great relief to the eye. 

There is one other thing of great importance to be considered inpurchasing a telescope--the mounting. If your glass is not well mountedon a steady and easily managed stand, you might better have spent yourmoney for something more useful. I have endured hours of torment whiletrying to see stars through a telescope that was shivering in the windand dancing to every motion of the bystanders, to say nothing of thewriggling contortions caused by the application of my own fingers to thefocusing screw. The best of all stands is a solid iron pillar firmlyfastened into a brick or stone pier, sunk at least four feet in theground, and surmounted by a well-made equatorial bearing whose polaraxis has been carefully placed in the meridian. It can be readilyprotected from the weather by means of a wooden hood or a rubber sheet, while the tube of the telescope may be kept indoors, being carried outand placed on its bearing only when observations are to be made. Withsuch a mounting you can laugh at the observatories with their cumbersomedomes, for the best of all observatories is the open air. But if youdislike the labor of carrying and adjusting the tube every time it isused, and are both fond of and able to procure luxuries, then, afterall, perhaps, you had better have the observatory, dome, draughts andall. 

The next best thing in the way of a mounting is a portable tripod stand. This may be furnished either with an equatorial bearing for thetelescope, or an altazimuth arrangement which permits both up-and-downand horizontal motions. The latter is cheaper than the equatorial andproportionately inferior in usefulness and convenience. The essentialprinciple of the equatorial bearing is motion about two axes placed atright angles to one another. When the polar axis is in the meridian, andinclined at an angle equal to the latitude of the place, the telescopecan be moved about the two axes in such a way as to point to any quarterof the sky, and the motion of a star, arising from the earthy rotation, can be followed hour after hour without disturbing the instrument. Whenthus mounted, the telescope may be driven by clockwork, or by hand withthe aid of a screw geared to a handle carrying a universal joint. 

And now for testing the telescope. It has already been remarked that theexcellence of a telescope depends upon the perfection of the imageformed at the focus of the objective. In what follows I have only arefractor in mind, although the same principles would apply to areflector. With a little practice anybody who has a correct eye can forma fair judgment of the excellence of a telescopic image. Suppose we haveour telescope steadily mounted out of doors (if you value your peace ofmind you will not try to use a telescope pointed out of a window, especially in winter), and suppose we begin our observations with thepole star, employing a magnifying power of sixty or seventy to the inch. Our first object is to see if the optician has given us a good glass. Ifthe air is not reasonably steady we had better postpone our experimentto another night, because we shall find that the star as seen in thetelescope flickers and "boils, " and behaves in so extraordinary afashion that there is no more definition in the image than there issteadiness in a bluebottle buzzing on a window pane. But if the night isa fine one the star image will be quiescent, and then we may note thefollowing particulars: The real image is a minute bright disk, about onesecond of arc in diameter if we are using a four-and-a-half or five-inchtelescope, and surrounded by one very thin ring of light, and thefragments, so to speak, of one or possibly two similar rings a littlefarther from the disk, and visible, perhaps, only by glimpses. These"diffraction rings" arise from the undulatory nature of light, and theirdistance apart as well as the diameter of the central disk depend uponthe length of the waves of light. If the telescope is a really good one, and both object glass and eyepiece are properly adjusted, the disk willbe perfectly round, slightly softer at the edge, but otherwise equallybright throughout; and the ring or rings surrounding it will be exactlyconcentric, and not brighter on one side than on another. Even if ourtelescope were only two inches or two inches and a half in aperture weshould at once notice a little bluish star, the mere ghost of a star ina small telescope, hovering near the polar star. It is the celebrated"companion, " but we shall see it again when we have more time to studyit. Now let us put the star out of focus by turning the focusing screw. Suppose we turn it in such a way that the eyepiece moves slightlyoutside the focus, or away from the object glass. Very beautifulphenomena immediately begin to make their appearance. A slight motionoutward causes the little disk to expand perceptibly, and just as thisexpansion commences, a bright-red point appears at the precise center ofthe disk. But, the outward motion continuing, this red centerdisappears, and is replaced by a blue center, which gradually expandsinto a sort of flare over the middle of the disk. The disk itself has inthe mean time enlarged into a series of concentric bright rings, graduated in luminosity with beautiful precision from center towardcircumference. The outermost ring is considerably brighter, however, than it would be if the same gradation applied to it as applies to theinner rings, and it is surrounded, moreover, on its outer edge by aslight flare which tends to increase its apparent width. Next let usreturn to the focus and then move the eyepiece gradually inside thefocal point or plane. Once more the star disk expands into a series ofcircles, and, if we except the color phenomena noticed outside thefocus, these circles are precisely like those seen before inarrangement, in size, and in brightness. If they were not the same, weshould pronounce the telescope to be imperfect. There is one otherdifference, however, besides the absence of the blue central flare, andthat is a faint reddish edging around the outer ring when the expansioninside the focus is not carried very far. Upon continuing to move theeyepiece inside or outside the focus we observe that the system of ringsbecomes larger, while the rings themselves rapidly increase in number, becoming at the same time individually thinner and fainter. 

[Illustration: THE STAR IMAGE. ]

By studying the appearance of the star disk when in focus and of therings when out of focus on either side, an experienced eye can readilydetect any fault that a telescope may have. The amateur, of course, canonly learn to do this by considerable practice. Any glaring and seriousfault, however, will easily make itself manifest. Suppose, for example, we observe that the image of a star instead of being perfectly round isoblong, and that a similar defect appears in the form of the rings whenthe eyepiece is put out of focus. We know at once that something iswrong; but the trouble may lie either in the object glass, in theeyepiece, in the eye of the observer himself, or in the adjustment ofthe lenses in the tube. A careful examination of the image and theout-of-focus circles will enable us to determine with which of thesesources of error we have to deal. If the star image when in focus has asort of wing on one side, and if the rings out of focus expandeccentrically, appearing wider and larger on one side than on the other, being at the same time brightest on the least expanded side, then theobject glass is probably not at right angles to the axis of the tube andrequires readjustment. That part of the object glass on the side wherethe rings appear most expanded and faintest needs to be pushed slightlyinward. This can be effected by means of counterscrews placed for thatpurpose in or around the cell. But it, after we have got the objectglass properly squared to the axis of the tube or the line of sight, theimage and the ring system in and out of focus still appear oblong, thefault of astigmatism must exist either in the objective, the eyepiece, or the eye. The chances are very great that it is the eye itself that isat fault. We may be certain of this if we find, on turning the head soas to look into the telescope with the eye in different positions, thatthe oblong image turns with the head of the observer, keeping its majoraxis continually in the same relative position with respect to the eye. The remedy then is to consult an oculist and get a pair of cylindricaleyeglasses. If the oblong image does not turn round with the eye, butdoes turn when the eyepiece is twisted round, then the astigmatism is inthe latter. If, finally, it does not follow either the eye or theeyepiece, it is the objective that is at fault. 

But instead of being oblong, the image and the rings may be misshapen insome other way. If they are three-cornered, it is probable that theobject glass is subjected to undue pressure in its cell. This, if thetelescope has been brought out on a cool night from a warm room, mayarise from the unequal contraction of the metal work and the glass asthey cool off. In fact, no good star image can be got while a telescopeis assuming the temperature of the surrounding atmosphere. Even the airinclosed in the tube is capable of making much trouble until itstemperature has sunk to the level of that outside. Half an hour at leastis required for a telescope to adjust itself to out-of-door temperature, except in the summer time, and it is better to allow an hour or two forsuch adjustment in cold weather. Any irregularity in the shape of therings which persists after the lenses have been accurately adjusted andthe telescope has properly cooled may be ascribed to imperfections, suchas veins or spots of unequal density in the glass forming the objective. 

[Illustration: THE OUT-OF-FOCUS RINGS. 

1, Correct figure; 2 and 3, spherical aberration. ]

The spherical aberration of an object glass may be undercorrected orovercorrected. In the former case the central rings inside the focuswill appear faint and the outer ones unduly strong, while outside thefocus the central rings will be too bright and the outer ones toofeeble. But if the aberration is overcorrected the central rings will beoverbright inside the focus and abnormally faint outside the focus. 

[Illustration: TWO VIEWS OF MARS IN 1892. 

The smaller with a three-and-three-eighths-inch telescope; the largerwith a nine-inch. ]

Assuming that we have a telescope in which no obvious fault isdiscernible, the next thing is to test its powers in actual work. Inwhat is to follow I shall endeavor to describe some of the principalobjects in the heavens from which the amateur observer may expect toderive pleasure and instruction, and which may at the same time serveas tests of the excellence of his telescope. No one should be deterredor discouraged in the study of celestial objects by the apparentinsignificance of his means of observation. The accompanying pictures ofthe planet Mars may serve as an indication of the fact that a smalltelescope is frequently capable of doing work that appears by no meanscontemptible when placed side by side with that of the greaterinstruments of the observatories. 

CHAPTER II

IN THE STARRY HEAVENS

"Now constellations, Muse, and signs rehearse;In order let them sparkle in thy verse. "--MANILIUS. 

Let us imagine ourselves the happy possessors of three properly mountedtelescopes of five, four, and three inches aperture, respectively. Afine midwinter evening has come along, the air is clear, cool, andsteady, and the heavens, of that almost invisible violet which isreserved for the lovers of celestial scenery, are spangled with starsthat hardly twinkle. We need not disturb our minds about a few thinclouds here and there floating lazily in the high air; they announce achange of weather, but they will not trouble us to-night. 

Which way shall we look? Our eyes will answer the question for us. However we may direct them, they instinctively return to the south, andare lifted to behold Orion in his glory, now near the meridian andmidway to the zenith, with Taurus shaking the glittering Pleiades beforehim, and Canis Major with the flaming Dog Star following at his heels. 

Not only is Orion the most brilliant of all constellations to the casualstar-gazer, but it contains the richest mines that the delver fortelescopic treasures can anywhere discover. We could not have made abetter beginning, for here within a space of a few square degrees wehave a wonderful variety of double stars and multiple stars, so closeand delicate as to test the powers of the best telescopes, besides aprofusion of star-clusters and nebulæ, including one of the suprememarvels of space, the Great Nebula in the Sword. 

[Illustration: MAP NO. 1. ]

Our star map No. 1 will serve as a guide to the objects which we areabout to inspect. Let us begin operations with our smallest telescope, the three-inch. I may remark here that, just as the lowest magnifyingpower that will clearly reveal the object looked for gives ordinarilybetter results than a higher power, so the smallest telescope that iscompetent to show what one wishes to see is likely to yield moresatisfaction, as far as that particular object is concerned, than alarger glass. The larger the object glass and the higher the power, thegreater are the atmospheric difficulties. A small telescope will performvery well on a night when a large one is helpless. 

Turn the glass upon beta (Rigel), the white first-magnitude star inOrion's left foot. Observe whether the image with a high power is clear, sharp, and free from irregular wisps of stray light. Look at the ringsin and out of focus, and if you are satisfied with the performance, tryfor the companion. A good three-inch is certain to show it, except in abad state of the atmosphere, and even then an expert can see it, atleast by glimpses. The companion is of the ninth magnitude, some say theeighth, and the distance is about 9. 5", angle of position (hereafterdesignated by p. ) 199°. [1] Its color is blue, in decided contrast withthe white light of its great primary. Sir John Herschel, however, sawthe companion red, as others have done. These differences are doubtlessdue to imperfections of the eye or the telescope. In 1871 Burnhambelieved he had discovered that the companion was an exceedingly closedouble star. No one except Burnham himself succeeded in dividing it, andhe could only do so at times. Afterward, when he was at Mount Hamilton, he tried in vain to split it with the great thirty-six-inch telescope, in 1889, 1890, and 1891. His want of success induced him to suggest thatthe component stars were in rapid motion, and so, although he admittedthat it might not be double after all, he advised that it should bewatched for a few years longer. His confidence was justified, for in1898 Aitken, with the Lick telescope, saw and measured the distance ofthe extremely minute companion--distance 0. 17", p. 177°. 

[1] The angle of position measures the inclination to the meridian of aline drawn between the principal star and its companion; in other words, it shows in what direction from the primary we must look for thecompanion. It is reckoned from 0° up to 360°, beginning at the northpoint and passing around by east through south and west to north again. Thus, if the angle of position is 0° or 360°, the companion is on thenorth side of the primary; if the angle is 90°, the companion is to theeast; if 180°, to the south; if 270°, to the west, and so forintermediate angles. It must be remembered, however, that in the fieldof the telescope the top is south and the bottom north, unless a prismis used, when directions become complicated. East and west can bereadily identified by noticing the motion of a star through the field;it moves toward the west and from the east. 

Rigel has been suspected of a slight degree of variability. It isevidently a star of enormous actual magnitude, for its parallax escapestrustworthy measurement. It can only be ranked among the very first ofthe light-givers of the visible universe. Spectroscopically it belongsto a peculiar type which has very few representatives among the brightstars, and which has been thus described: "Spectra in which the hydrogenlines and the few metallic lines all appear to be of equal breadth andsharp definition. " Rigel shows a line which some believe to representmagnesium; but while it has iron lines in its spectrum, it exhibits noevidence of the existence of any such cloud of volatilized iron as thatwhich helps to envelop the sun. 

For another test of what the three-inch will do turn to zeta, the lower, or left-hand, star in the Belt. This is a triple, the magnitudes beingsecond, sixth, and tenth. The sixth-magnitude star is about 2. 5" fromthe primary, p. 149°, and has a very peculiar color, hard to describe. It requires careful focusing to get a satisfactory view of this starwith a three-inch telescope. Use magnifying powers up to two hundred andfifty diameters. With our four-inch the star is much easier, and thefive-inch shows it readily with a power of one hundred. Thetenth-magnitude companion is distant 56", p. 8°, and may be glimpsedwith the three-inch. Upon the whole, we shall find that we get morepleasing views of zeta Orionis with the four-inch glass. 

Just to the left of zeta, and in the same field of view with a very lowpower, is a remarkable nebula bearing the catalogue number 1227. We mustuse our five-inch on this with a low power, but with zeta out of thefield in order to avoid its glare. The nebula is exceedingly faint, andwe can be satisfied if we see it simply as a hazy spot, although withmuch larger telescopes it has appeared at least half a degree broad. Tempel saw several centers of condensation in it, and traced three orfour broad nebulous streams, one of which decidedly suggested spiralmotion. 

The upper star in the Belt, delta, is double; distance, 53", p. 360°;magnitudes, second and seventh very nearly; colors, white and green orblue. This, of course, is an easy object for the three-inch with a lowmagnifying power. It would be useless to look for the two faintercompanions of delta, discovered by Burnham, even with our five-inchglass. But we shall probably need the five-inch for our next attempt, and it will be well to put on a high power, say three hundred diameters. The star to be examined is the little brilliant dangling below theright-hand end of the Belt, toward Rigel. It appears on the map as eta. Spare no pains in getting an accurate focus, for here is something worthlooking at, and unless you have a trained eye you will not easily seeit. The star is double, magnitudes third and sixth, and the distancefrom center to center barely exceeds 1", p. 87°. A little tremulousnessof the atmosphere for a moment conceals the smaller star, although itspresence is manifest from the peculiar jutting of light on one side ofthe image of the primary. But in an instant the disturbing undulationspass, the air steadies, the image shrinks and sharpens, and two pointsof piercing brightness, almost touching one another, dart into sight, the more brilliant one being surrounded by an evanescent circle, a tinyripple of light, which, as it runs round the star and then recedes, alternately embraces and releases the smaller companion. The wash of thelight-waves in the atmosphere provokes many expressions of impatiencefrom the astronomer, but it is often a beautiful phenomenonnevertheless. 

Between eta and delta is a fifth-magnitude double star, Sigma 725, whichis worth a moment's attention. The primary, of a reddish color, has avery faint star, eleventh magnitude, at a distance of 12. 7", p. 88°. 

Still retaining the five-inch in use, we may next turn to the other endof the Belt, where, just under zeta, we perceive the fourth-magnitudestar sigma. He must be a person of indifferent mind who, after lookingwith unassisted eyes at the modest glimmering of this little star, cansee it as the telescope reveals it without a thrill of wonder and a cryof pleasure. The glass, as by a touch of magic, changes it from one intoeight or ten stars. There are two quadruple sets three and a halfminutes of arc apart. The first set exhibits a variety of beautifulcolors. The largest star, of fourth magnitude, is pale gray; the secondin rank, seventh magnitude, distance 42", p. 61°, presents a singularred, "grape-red" Webb calls it; the third, eighth magnitude, distance12", p. 84°, is blue; and the fourth, eleventh magnitude, distance 12", p. 236°, is apparently white. Burnham has doubled the fourth-magnitudestar, distance 0. 23". The second group of four stars consists of threeof the eighth to ninth magnitude, arranged in a minute triangle with amuch fainter star near them. Between the two quadruple sets carefulgazing reveals two other very faint stars. While the five-inch gives amore satisfactory view of this wonderful multiple star than any smallertelescope can do, the four-inch and even the three-inch would have shownit to us as a very beautiful object. However we look at them, there isan appearance of association among these stars, shining with theircontrasted colors and their various degrees of brilliance, which issignificant of the diversity of conditions and circumstances under whichthe suns and worlds beyond the solar walk exist. 

From sigma let us drop down to see the wonders of Orion's Sworddisplayed just beneath. We can use with advantage any one of our threetelescopes; but since we are going to look at a nebula, it is fortunatethat we have a glass so large as five inches aperture. It will revealinteresting things that escape the smaller instruments, because itgrasps more than one and a half times as much light as the four-inch, and nearly three times as much as the three-inch; and in dealing withnebulæ a plenty of light is the chief thing to be desired. The middlestar in the Sword is theta, and is surrounded by the celebrated Nebulaof Orion. The telescope shows theta separated into four stars arrangedat the corners of an irregular square, and shining in a black gap in thenebula. These four stars are collectively named the Trapezium. Thebrightest is of the sixth magnitude, the others are of the seventh, seven and a half, and eighth magnitudes respectively. The radiant mistabout them has a faint greenish tinge, while the four stars, togetherwith three others at no great distance, which follow a fold of thenebula like a row of buttons on a coat, always appear to me to show anextraordinary liveliness of radiance, as if the strange haze served toset them off. 

[Illustration: THE TRAPEZIUM WITH THE FIFTH AND SIXTH STARS. ]

Our three-inch would have shown the four stars of the Trapeziumperfectly well, and the four-inch would have revealed a fifth star, veryfaint, outside a line joining the smallest of the four and its nearestneighbor. But the five-inch goes a step farther and enables us, withsteady gazing to see even a sixth star, of only the twelfth magnitude, just outside the Trapezium, near the brightest member of the quartet. The Lick telescope has disclosed one or two other minute points of lightassociated with the Trapezium. But more interesting than the Trapeziumis the vast cloud, full of strange shapes, surrounding it. Nowhere elsein the heavens is the architecture of a nebula so clearly displayed. Itis an unfinished temple whose gigantic dimensions, while exalting theimagination, proclaim the omnipotence of its builder. But thoughunfinished it is not abandoned. The work of creation is proceedingwithin its precincts. There are stars apparently completed, shining likegems just dropped from the hand of the polisher, and around them aremasses, eddies, currents, and swirls of nebulous matter yet to becondensed, compacted, and constructed into suns. It is an education inthe nebular theory of the universe merely to look at this spot with agood telescope. If we do not gaze at it long and wistfully, and returnto it many times with unflagging interest, we may be certain that thereis not the making of an astronomer in us. 

Before quitting the Orion nebula do not fail to notice aneighth-magnitude star, a short distance northeast of the Great Nebula, and nearly opposite the broad opening in the latter that leads in towardthe gap occupied by the Trapezium. This star is plainly enveloped innebulosity, that is unquestionably connected with the larger mass ofwhich it appears to form a satellite. 

At the lower end of the Sword is the star iota, somewhat under the thirdmagnitude. Our three-inch will show that it has a bluish companion ofseventh or eighth magnitude, at a little more than 11" distance, p. 142°, and the larger apertures will reveal a third star, of tenthmagnitude, and reddish in color, distance 49", p. 103°. Close by iota wefind the little double star Sigma 747, whose components are of five anda half and six and a half magnitudes respectively, and separated 36", p. 223°. Above the uppermost star in the Sword is a small star cluster, No. 1184, which derives a special interest from the fact that it incloses adelicate double star, Sigma 750, whose larger component is of the sixthmagnitude, while the smaller is of the ninth, and the distance is only4. 3", p. 59°. We may try the four-inch on this object. 

Having looked at alpha (Betelgeuse), the great topaz star on Orion'sright shoulder, and admired the splendor of its color, we may turn thefour-inch upon the star Sigma 795, frequently referred to by its numberas "52 Orionis. " It consists of one star of the sixth and another ofsixth and a half magnitude, only 1. 5" apart, p. 200°. Having separatedthem with a power of two hundred and fifty diameters on the four-inch, we may try them with a high power on the three-inch. We shall onlysucceed this time if our glass is of first-rate quality and the air isperfectly steady. 

The star lambda in Orion's head presents an easy conquest for thethree-inch, as it consists of a light-yellow star of magnitude three anda half and a reddish companion of the sixth magnitude; distance 4", p. 43°. There is also a twelfth-magnitude star at 27", p. 183°, and a tenthor eleventh magnitude one at 149", p. 278°. These are tests for thefive-inch, and we must not be disappointed if we do not succeed inseeing the smaller one even with that aperture. 

Other objects in Orion, to be found with the aid of our map, are: Sigma627, a double star, magnitude six and a half and seven, distance 21", p. 260°; Omicron Sigma 98, otherwise named iota Orionis, double, magnitudesix and seven, distance 1", p. 180°, requires five-inch glass; Sigma652, double, magnitudes six and a half and eight, distance 1. 7", p. 184°; rho, double, magnitudes five and eight and a half, the latterblue, distance 7", p. 62°, may be tried with a three-inch; tau, triplestar, magnitudes four, ten and a half, and eleven, distances 36", p. 249°, and 36", p. 60°. Burnham discovered that the ten-and-a-halfmagnitude star is again double, distance 4", p. 50°. There is not muchsatisfaction in attempting tau Orionis with telescopes of ordinaryapertures; Sigma 629 otherwise _m_ Orionis, double, magnitudes five anda half (greenish) and seven, distance 31. 7", p. 28°, a pretty object;Sigma 728, otherwise A 32, double, magnitudes five and seven, distance, 0. 5" or less, p. 206°, a rapid binary, [2] which is at present too closefor ordinary telescopes, although it was once within their reach; Sigma729, double, magnitudes six and eight, distance 2", p. 26°, the smallerstar pale blue--try it with a four-inch, but five-inch is better; Sigma816, double, magnitudes six and half and eight and a half, distance 4", p. 289°; psi 2, double, magnitudes five and a half and eleven, distance3", or a little less, p. 322°; 905, star cluster, contains about twentystars from the eighth to the eleventh magnitude; 1267, nebula, faint, containing a triple star of the eighth magnitude, two of whosecomponents are 51" apart, while the third is only 1. 7" from itscompanion, p. 85°; 1376, star cluster, small and crowded; 1361, starcluster, triangular shape, containing thirty stars, seventh to tenthmagnitudes, one of which is a double, distance 2. 4". 

[2] The term "binary" is used to describe double stars which are inmotion about their common center of gravity. 

Let us now leave the inviting star-fields of Orion and take a glance atthe little constellation of Lepus, crouching at the feet of the mythicalgiant. We may begin with a new kind of object, the celebrated redvariable R Leporis (map No. 1). This star varies from the sixth orseventh magnitude to magnitude eight and a half in a period of fourhundred and twenty-four days. Hind's picturesque description of itscolor has frequently been quoted. He said it is "of the most intensecrimson, resembling a blood-drop on the black ground of the sky. " It isimportant to remember that this star is reddest when faintest, so thatif we chance to see it near its maximum of brightness it will notimpress us as being crimson at all, but rather a dull, coppery red. Itsspectrum indicates that it is smothered with absorbing vapors, a sunnear extinction which, at intervals, experiences an accession of energyand bursts through its stifling envelope with explosive radiance, onlyto faint and sink once more. It is well to use our largest aperture inexamining this star. 

We may also employ the five-inch for an inspection of the double stariota, whose chief component of the fifth magnitude is beautifully tingedwith green. The smaller companion is very faint, eleventh magnitude, andthe distance is about 13", p. 337°. 

Another fine double in Lepus is kappa, to be found just below iota; thecomponents are of the fifth and eighth magnitudes, pale yellow and bluerespectively, distance 2. 5", p. 360°; the third-magnitude star alpha hasa tenth-magnitude companion at a distance of 35", p. 156°, and itsneighbor beta (map No. 2), according to Burnham, is attended by threeeleventh-magnitude stars, two of which are at distances of 206", p. 75°, and 240", p. 58°, respectively, while the third is less than 3" frombeta, p. 288°; the star gamma (map No. 2) is a wide double, the distancebeing 94", and the magnitudes four and eight. The star numbered 45 is aremarkable multiple, but the components are too faint to possess muchinterest for those who are not armed with very powerful telescopes. 

[Illustration: MAP NO. 2. ]

From Lepus we pass to Canis Major (map No. 2). There is no hope of ourbeing able to see the companion of alpha (Sirius), at present (1901), even with our five-inch. Discovered by Alvan Clark with an eighteen-inchtelescope in 1862, when its distance was 10" from the center of Sirius, this ninth-magnitude star has since been swallowed up in the blaze ofits great primary. At first, it slightly increased its distance, andfrom 1868 until 1879 most of the measures made by different observersconsiderably exceeded 11". Then it began to close up, and in 1890 thedistance scarcely exceeded 4". Burnham was the last to catch sight of itwith the Lick telescope in that year. After that no human eye saw ituntil 1896, when it was rediscovered at the Lick Observatory. Sincethen the distance has gradually increased to nearly 5". According toBurnham, its periodic time is about fifty-three years, and its nearestapproach to Sirius should have taken place in the middle of 1892. Latercalculations reduce the periodic time to forty-eight or forty-nineyears. If we can not see the companion of the Dog Star with ourinstruments, we can at least, while admiring the splendor of thatdazzling orb, reflect with profit upon the fact that although thecompanion is ten thousand times less bright than Sirius, it is half asmassive as its brilliant neighbor. Imagine a subluminous body half asponderous as the sun to be set revolving round it somewhere betweenUranus and Neptune. Remember that that body would possess one hundredand sixty-five thousand times the gravitating energy of the earth, andthat five hundred and twenty Jupiters would be required to equal itspower of attraction, and then consider the consequences to oureasy-going planets! Plainly the solar system is not cut according to theSirian fashion. We shall hardly find a more remarkable coupling ofcelestial bodies until we come, on another evening, to a star thatbegan, ages ago, to amaze the thoughtful and inspire the superstitiouswith dread--the wonderful Algol in Perseus. 

We may remark in passing that Sirius is the brightest representative ofthe great spectroscopic type I, which includes more than half of all thestars yet studied, and which is characterized by a white or bluish-whitecolor, and a spectrum possessing few or at best faint metallic lines, but remarkably broad, black, and intense lines of hydrogen. Theinference is that Sirius is surrounded by an enormous atmosphere ofhydrogen, and that the intensity of its radiation is greater, surfacefor surface, than that of the sun. There is historical evidence tosupport the assertion, improbable in itself, that Sirius, withineighteen hundred years, has changed color from red to white. 

With either of our telescopes we shall have a feast for the eye when weturn the glass upon the star cluster No. 1454, some four degrees southof Sirius. Look for a red star near the center. Observe the curving rowsso suggestive of design, or rather of the process by which this clusterwas evolved out of a pre-existing nebula. You will recall the windingstreams in the Great Nebula of Orion. Another star cluster worth amoment's attention is No. 1479, above and to the left of Sirius. We hadbetter use the five-inch for this, as many of the stars are very faint. Not far away we find the double star, whose components are of the fifthand eighth magnitudes, distance 2. 8", p. 343°. The small star is paleblue. Cluster No. 1512 is a pleasing object with our largest aperture. In No. 1511 we have a faint nebula remarkable for the rows of minutestars in and near it. The star gamma is an irregular variable. In 1670it is said to have almost disappeared, while at the beginning of theeighteenth century it was more than twice as bright as it is to-day. Thereddish star delta is also probably variable. In my "Astronomy with anOpera Glass" will be found a cut showing a singular array of small starspartly encircling delta. These are widely scattered by a telescope, evenwith the lowest power. 

Eastward from Canis Major we find some of the stars of Argo Navis. Sigma1097, of the sixth magnitude, has two minute companions at 20" distance, p. 311° and 312°. The large star is itself double, but the distance, 0. 8", p. 166°, places it beyond our reach. According to Burnham, thereis yet a fourth faint star at 31", p. 40°. Some three degrees and a halfbelow and to the left of the star just examined is a beautiful starcluster, No. 1551. Nos. 1564, 1571, and 1630 are other star clusterswell worth examination. A planetary nebula is included in 1564. Withvery powerful telescopes this nebula has been seen ring-shaped. Sigma1146, otherwise known as 5 Navis, is a pretty double, colors pale yellowand blue, magnitudes five and seven, distance 3. 25", p. 19°. Ourthree-inch will suffice for this. 

[Illustration: MAP NO. 3. ]

North of Canis Major and Argo we find Monoceros and Canis Minor (map No. 3). The stars forming the western end of Monoceros are depicted on mapNo. 1. We shall begin with these. The most interesting and beautiful is11, a fine triple star, magnitudes five, six, and seven, distances 7. 4", p. 131°, and 2. 7", p. 103°. Sir William Herschel regarded this as one ofthe most beautiful sights in the heavens. It is a good object to try ourthree-inch on, although it should not be difficult for such an aperture. The star 4 is also a triple, magnitudes six, ten, and eleven, distances3. 4", p. 178°, and 10", p. 244°. We should glance at the star 5 toadmire its fine orange color. In 8 we find a golden fifth-magnitudestar, combined with a blue or lilac star of the seventh magnitude, distance 14", p. 24°. Sigma 938 is a difficult double, magnitudes sixand a half and twelve, distance 10", p. 210°. Sigma 921 is double, magnitudes six and a half and eight, distance 16", p. 4°. At the spotmarked on the map 1424 we find an interesting cluster containing onestar of the sixth magnitude. 

The remaining stars of Monoceros will be found on map No. 3. The doubleand triple stars to be noted are S, or Sigma 950 (which is also avariable and involved in a faint nebula), magnitudes six and nine, distance 2. 5", p. 206°; Sigma 1183, double, magnitudes five and a halfand eight, distance 31", p. 326°; Sigma 1190, triple, magnitudes fiveand a half, ten, and nine, distances 31", p. 105°, and 67", p. 244°. The clusters are 1465, which has a minute triple star near the center;1483, one member of whose swarm is red; 1611, very small but rich; and1637, interesting for the great number of ninth-magnitude stars that itcontains. We should use the five-inch for all of these. 

Canis Minor and the Head of Hydra are also contained on map No. 3. Procyon, alpha of Canis Minor, has several minute stars in the samefield of view. There is, besides, a companion which, although it wasknown to exist, no telescope was able to detect until November, 1896. Itmust be of immense mass, since its attraction causes perceptibleperturbations in the motion of Procyon. Its magnitude is eight and ahalf, distance 4. 83", p. 338°. One of the small stars just referred to, the second one east of Procyon, distant one third of the moon'sdiameter, is an interesting double. Our four-inch may separate it, andthe five-inch is certain to do so. The magnitudes are seven and sevenand a half or eight, distance 1. 2", p. 133°. This star is variouslynamed Sigma 1126 and 31 Can. Min. Bode. Star No. 14 is a wide triple, magnitudes six, seven, and eight, distances 75, p. 65°, and 115", p. 154°. 

PROCYON AND ITS NEIGHBORS. 

In the Head of Hydra we find Sigma 1245, a double of the sixth andseventh magnitudes, distance 10. 5", p. 25°. The larger star shows a fineyellow. In epsilon we have a beautiful combination of a yellow with ablue star, magnitudes four and eight, distance 3. 4", p. 198°. Finally, let us look at theta for a light test with the five-inch. The two starscomposing it are of the fourth and twelfth magnitudes, distance 50", p. 170°. 

The brilliant constellations of Gemini and Taurus tempt us next, butwarning clouds are gathering, and we shall do well to house ourtelescopes and warm our fingers by the winter fire. There will be otherbright nights, and the stars are lasting. 

CHAPTER III

FROM GEMINI TO LEO AND ROUND ABOUT

"If thou wouldst gaze on starry Charioteer, And hast heard legends of the wondrous Goat, Vast looming shalt thou find on the Twins' left, His form bowed forward. "--POSTE'S ARATUS. 

[Illustration: MAP NO. 4. ]

The zodiacal constellations of Gemini, Cancer, and Leo, together withtheir neighbors Auriga, the Lynx, Hydra, Sextans, and Coma Berenices, will furnish an abundance of occupation for our second night at thetelescope. We shall begin, using our three-inch glass, with alpha, thechief star of Gemini (map No. 4). This is ordinarily known as Castor. Even an inexperienced eye perceives at once that it is not as bright asits neighbor Pollux, beta. Whether this fact is to be regarded asindicating that Castor was brighter than Pollux in 1603, when Bayerattached their Greek letters, is still an unsettled question. Castor mayor may not be a variable, but it is, at any rate, one of the mostbeautiful double stars in the heavens. A power of one hundred is amplysufficient to separate its components, whose magnitudes are about twoand three, the distance between them being 6", p. 226°. A slight yetdistinct tinge of green, recalling that of the Orion nebula, gives apeculiar appearance to this couple. Green is one of the rarest colorsamong the stars. Castor belongs to the same general spectroscopic typein which Sirius is found, but its lines of hydrogen are broader thanthose seen in the spectrum of the Dog Star. There is reason forthinking that it may be surrounded with a more extensive atmosphere ofthat gaseous metal called hydrogen than any other bright star possesses. There seems to be no doubt that the components of Castor are inrevolution around their common center of gravity, although the period isuncertain, varying in different estimates all the way from two hundredand fifty to one thousand years; the longer estimate is probably not farfrom the truth. There is a tenth-magnitude star, distance 73", p. 164°, which may belong to the same system. 

From Castor let us turn to Pollux, at the same time exchanging ourthree-inch telescope for the four-inch, or, still better, the five-inch. Pollux has five faint companions, of which we may expect to see three, as follows: Tenth magnitude, distance 175", p. 70°; nine and a halfmagnitude, distance 206", p. 90°, and ninth magnitude, distance 229", p. 75°. Burnham has seen a star of thirteen and a half magnitude, distance43", p. 275°, and has divided the tenth-magnitude star into twocomponents, only 1. 4" apart, the smaller being of the thirteenthmagnitude, and situated at the angle 128°. A calculation based on Dr. Elkin's parallax of 0. 068" for Pollux shows that that star may be ahundredfold more luminous than the sun, while its nearest companion maybe a body smaller than our planet Jupiter, but shining, of course, byits own light. Its distance from Pollux, however, exceeds that ofJupiter from the sun in the ratio of about one hundred and thirty toone. 

In the double star pi we shall find a good light test for our three-inchaperture, the magnitudes being six and eleven, distance 22", p. 212°. The four-inch will show that kappa is a double, magnitudes four and ten, distance 6", p. 232°. The smaller star is of a delicate blue color, andit has been suspected of variability. That it may be variable isrendered the more probable by the fact that in the immediateneighborhood of kappa there are three undoubted variables, S, T, and U, and there appears to be some mysterious law of association which causessuch stars to group themselves in certain regions. None of the variablesjust named ever become visible to the naked eye, although they allundergo great changes of brightness, sinking from the eighth or ninthmagnitude down to the thirteenth or even lower. The variable R, whichlies considerably farther west, is well worth attention because of theremarkable change of color which it sometimes exhibits. It has been seenblue, red, and yellow in succession. It varies from between the sixthand seventh magnitudes to less than the thirteenth in a period of abouttwo hundred and forty-two days. 

Not far away we find a still more curious variable zeta; this is also aninteresting triple star, its principal component being a little underthe third magnitude, while one of the companions is of the seventhmagnitude, distance 90", p. 355°, and the other is of the eleventhmagnitude or less, distance 65", p. 85°. We should hardly expect to seethe fainter companion with the three-inch. The principal star variesfrom magnitude three and seven tenths down to magnitude four and a halfin a period of a little more than ten days. 

[Illustration: WONDERFUL NEBULA IN GEMINI (1532). ]

With the four-or five-inch we get a very pretty sight in delta, whichappears split into a yellow and a purple star, magnitudes three andeight, distance 7", p. 206°. 

Near delta, toward the east, lies one of the strangest of all thenebulæ. (See the figures 1532 on the map. ) Our telescopes will show itto us only as a minute star surrounded with a nebulous atmosphere, butits appearance with instruments of the first magnitude is soastonishing and at the same time so beautiful that I can not refrainfrom giving a brief description of it as I saw it in 1893 with the greatLick telescope. In the center glittered the star, and spread evenlyaround it was a circular nebulous disk, pale yet sparkling andconspicuous. This disk was sharply bordered by a narrow _black_ ring, and outside the ring the luminous haze of the nebula again appeared, gradually fading toward the edge to invisibility. The accompanying cut, which exaggerates the brightness of the nebula as compared with thestar, gives but a faint idea of this most singular object. If itspeculiarities were within the reach of ordinary telescopes, there arefew scenes in the heavens that would be deemed equally admirable. 

In the star eta we have another long-period variable, which is also adouble star; unfortunately the companion, being of only the tenthmagnitude and distant less than 1" from its third-magnitude primary, isbeyond the reach of our telescopes. But eta points the way to one of thefinest star clusters in the sky, marked 1360 on the map. The naked eyeperceives that there is something remarkable in that place, and theopera glass faintly reveals its distant splendors, but the telescopefairly carries us into its presence. Its stars are innumerable, varyingfrom the ninth magnitude downward to the last limit of visibility, andpresenting a wonderful array of curves which are highly interesting fromthe point of view of the nebular origin of such clusters. Lookingbackward in time, with that theory to guide us, we can see spiral linesof nebulous mist occupying the space that now glitters with interlacingrows of stars. It is certainly difficult to understand how such lines ofnebula could become knotted with the nuclei of future stars, and thengradually be absorbed into those stars; and yet, if such a process doesnot occur, what is the meaning of that narrow nebulous streak in thePleiades along which five or six stars are strung like beads on astring? The surroundings of this cluster, 1360, as one sweeps over themwith the telescope gradually drawing toward the nucleus, have oftenreminded me of the approaches to such a city as London. Thicker andcloser the twinkling points become, until at last, as the observers eyefollows the gorgeous lines of stars trending inward, he seems to beentering the streets of a brilliantly lighted metropolis. 

Other objects in Gemini that we can ill miss are:, double, magnitudesthree and eleven, distance 73", p. 76°, colors yellow and blue; 15, double, magnitudes six and eight, distance 33", p. 205°; gamma, remarkable for array of small stars near it; 38, double, magnitudes sixand eight, distance 6. 5", p. 162°, colors yellow and blue (very pretty);lambda, double, magnitudes four and eleven, distance 10", p. 30°, colorof larger star blue--try with the five-inch; epsilon, double, magnitudesthree and nine, distance 110", p. 94°. 

From Gemini we pass to Cancer. This constellation has no large stars, but its great cluster Præsepe (1681 on map No. 4) is easily seen as astarry cloud with the naked eye. With the telescope it presents the mostbrilliant appearance with a very low power. It was one of the firstobjects that Galileo turned to when he had completed his telescope, andhe wonderingly counted its stars, of which he enumerated thirty-six, andmade a diagram showing their positions. 

The most interesting star in Cancer is zeta, a celebrated triple. Themagnitudes of its components are six, seven, and seven and a half;distances 1. 14", p. 6°, and 5. 7", p. 114°. We must use our five-inchglass in order satisfactorily to separate the two nearest stars. Thegravitational relationship of the three stars is very peculiar. Thenearest pair revolve around their common center in about fifty-eightyears, while the third star revolves with the other two, around a centercommon to all three, in a period of six or seven hundred years. But themovements of the third star are erratic, and inexplicable except uponthe hypothesis advanced by Seeliger, that there is an invisible, ordark, star near it by whose attraction its motion is perturbed. 

In endeavoring to picture the condition of things in zeta Cancri wemight imagine our sun to have a companion sun, a half or a third aslarge as itself, and situated within what may be called planetarydistance, circling with it around their center of gravity; while a thirdsun, smaller than the second and several times as far away, andaccompanied by a _black_ or non-luminous orb, swings with the first twoaround another center of motion. There you would have an entertainingcomplication for the inhabitants of a system of planets!

Other objects in Cancer are: Sigma 1223, double star, magnitudes six andsix and a half, distance 5", p. 214°; Sigma 1291, double, magnitudesboth six, distance 1. 3", p. 328°--four-inch should split it; iota, double, magnitudes four and a half and six and a half, distance 30", p. 308°; 66, double magnitudes six and nine, distance 4. 8", p. 136°; Sigma1311, double, magnitudes both about the seventh, distance 7", p. 200°;1712, star cluster, very beautiful with the five-inch glass. 

[Illustration: MAP NO. 5. ]

The constellation of Auriga may next command our attention (map No. 5). The calm beauty of its leading star Capella awakens an admiration thatis not diminished by the rivalry of Orion's brilliants glittering to thesouth of it. Although Capella must be an enormously greater sun thanours, its spectrum bears so much resemblance to the solar spectrum thata further likeness of condition is suggested. No close telescopiccompanion to Capella has been discovered. A ninth-magnitude companion, distant 159", p. 146°, and two others, one of twelfth magnitude at 78", p. 317°, the other of thirteenth magnitude at 126", p. 183°, may bedistant satellites of the great star, but not planets in the ordinarysense, since it is evident that they are self-luminous. It is asignificant fact that most of the first-magnitude stars have faintcompanions which are not so distant as altogether to preclude the ideaof physical relationship. 

But while Capella has no visible companion, Campbell, of the LickObservatory, has lately discovered that it is a conspicuous example of apeculiar class of binary stars only detected within the closing decadeof the nineteenth century. The nature of these stars, calledspectroscopic binaries, may perhaps best be described while we turn ourattention from Capella to the second star in Auriga beta (Menkalina), which not only belongs to the same class, but was the first to bediscovered. Neither our telescopes, nor any telescope in existence, candirectly reveal the duplicity of beta Aurigæ to the eye--i. E. , we cannot see the two stars composing it, because they are so close that theirlight remains inextricably mingled after the highest practicablemagnifying power has been applied in the effort to separate them. Butthe spectroscope shows that the star is double and that its componentsare in rapid revolution around one another, completing their orbitalswing in the astonishingly short period of _four days_! The combinedmass of the two stars is estimated to be two and a half times the massof the sun, and the distance between them, from center to center, isabout eight million miles. 

The manner in which the spectroscope revealed the existence of twostars in beta Aurigæ is a beautiful illustration of the unexpected and, so to speak, automatic application of an old principle in the discoveryof new facts not looked for. It was noticed at the Harvard Observatorythat the lines in the photographed spectrum of beta Aurigæ (and of a fewother stars to be mentioned later) appeared single in some of thephotographs and double in others. Investigation proved that the lineswere doubled at regular intervals of about two days, and that theyappeared single in the interim. The explanation was not far to seek. Itis known that all stars which are approaching us have their spectrallines shifted, by virtue of their motion of approach, toward the violetend of the spectrum, and that, for a similar reason, all stars which arereceding have their lines shifted toward the red end of the spectrum. Now, suppose two stars to be revolving around one another in a planehorizontal, or nearly so, to the line of sight. When they are at theirgreatest angular distance apart as seen from the earth one of them willevidently be approaching at the same moment that the other is receding. The spectral lines of the first will therefore be shifted toward theviolet, and those of the second will be shifted toward the red. Then ifthe stars, when at their greatest distance apart, are still so closethat the telescope can not separate them, their light will be combinedin the spectrum; but the spectral lines, being simultaneously shifted inopposite directions, will necessarily appear to be doubled. As therevolution of the stars continues, however, it is clear that theirmotion will soon cease to be performed in the line of sight, and willbecome more and more athwart that line, and as this occurs the spectrallines will gradually assume their normal position and appear single. This is the sequence of phenomena in beta Aurigæ. And the same sequenceis found in Capella and in several other more or less conspicuous starsin various parts of the heavens. 

Such facts, like those connecting rows and groups of stars with massesand spiral lines of nebula are obscure signboards, indicating theopening of a way which, starting in an unexpected direction, leads deepinto the mysteries of the universe. 

Southward from beta we find the star theta, which is a beautifulquadruple. We shall do best with our five-inch here, although in a finecondition of the atmosphere the four-inch might suffice. The primary isof the third magnitude; the first companion is of magnitude seven and ahalf, distance 2", p. 5°; the second, of the tenth magnitude, distance45", p. 292°; and the third, of the tenth magnitude, distance 125", p. 350°. 

We should look at the double Sigma 616 with one of our larger aperturesin order to determine for ourselves what the colors of the componentsare. There is considerable diversity of opinion on this point. Some saythe larger star is pale red and the smaller light blue; others considerthe color of the larger star to be greenish, and some have even calledit white. The magnitudes are five and nine, distance 6", p. 350°. 

Auriga contains several noteworthy clusters which will be found on themap. The most beautiful of these is 1295, in which about five hundredstars have been counted. 

The position of the new star of 1892, known as Nova Aurigæ, is alsoindicated on the map. While this never made a brilliant appearance, itgave rise to a greater variety of speculative theories than any previousphenomenon of the kind. Although not recognized until January 24, 1892, this star, as photographic records prove, was in existence on December9, 1891. At its brightest it barely exceeded magnitude four and a half, and its maximum occurred within ten days after its first recognition. When discovered it was of the fifth magnitude. It was last seen in itsoriginal form with the Lick telescope on April 26th, when it had sunk tothe lowest limit of visibility. To everybody's astonishment itreappeared in the following August, and on the 17th of that month wasseen shining with the light of a tenth-magnitude star, _but presentingthe spectrum of a nebula!_ Its visual appearance in the great telescopewas now also that of a planetary nebula. Its spectrum during the firstperiod of its visibility had been carefully studied, so that the meansexisted for making a spectroscopic comparison of the phenomenon in itstwo phases. During the first period, when only a stellar spectrum wasnoticed, remarkable shiftings of the spectral lines occurred, indicatingthat two and perhaps three bodies were concerned in the production ofthe light of the new star, one of which was approaching the earth, whilethe other or the others receded with velocities of several hundred milesper second! On the revival in the form of a planetary nebula, while thecharacter of the spectrum had entirely changed, evidences of rapidmotion in the line of sight remained. 

But what was the meaning of all this? Evidently a catastrophe of somekind had occurred out there in space. The idea of a collision involvingthe transformation of the energy of motion into that of light and heatsuggests itself at once. But what were the circumstances of thecollision? Did an extinguished sun, flying blindly through space, plungeinto a vast cloud of meteoric particles, and, under the lashing impactof so many myriads of missiles, break into superficial incandescence, while the cosmical wrack through which it had driven remained glowingwith nebulous luminosity? Such an explanation has been offered bySeeliger. Or was Vogel right when he suggested that Nova Aurigæ couldbe accounted for by supposing that a wandering dark body had run intocollision with a system of planets surrounding a decrepit sun (andtherefore it is to be hoped uninhabited), and that those planets hadbeen reduced to vapor and sent spinning by the encounter, the secondoutburst of light being caused by an outlying planet of the systemfalling a prey to the vagabond destroyer? Or some may prefer theexplanation, based on a theory of Wilsing's, that _two_ great bodies, partially or wholly opaque and non-luminous at their surfaces, butliquid hot within, approached one another so closely that the tremendousstrain of their tidal attraction burst their shells asunder so thattheir bowels of fire gushed briefly visible, amid a blaze of spoutingvapors. And yet Lockyer thinks that there was no solid or semisolid massconcerned in the phenomenon at all, but that what occurred was simplythe clash of two immense swarms of meteors that had crossed oneanother's track. 

Well, where nobody positively knows, everybody has free choice. In themeantime, look at the spot in the sky where that little star made itsappearance and underwent its marvelous transformation, for, even if youcan see no remains of it there, you will feel your interest in theproblem it has presented, and in the whole subject of astronomy, greatlyheightened and vivified, as the visitor to the field of Waterloo becomesa lover of history on the spot. 

The remaining objects of special interest in Auriga may be brieflymentioned: 26, triple star, magnitudes five, eight, and eleven, distances 12", p. 268°, and 26", p. 113°; 14, triple star, magnitudesfive, seven and a half, and eleven, distances 14", p. 224°, and 12. 6", p. 342°, the last difficult for moderate apertures; lambda, double, magnitudes five and nine, distance 121", p. 13°; epsilon, variable, generally of third magnitude, but has been seen of only four and a halfmagnitude; 41, double, magnitudes five and six, distance 8", p. 354°;996, 1067, 1119, and 1166, clusters all well worth inspection, 1119being especially beautiful. 

The inconspicuous Lynx furnishes some fine telescopic objects, allgrouped near the northwestern corner of the constellation. Without asix-inch telescope it would be a waste of time to attack the double star4, whose components are of sixth and eighth magnitudes, distance 0. 8", p. 103°; but its neighbor, 5, a fine triple, is within our reach, themagnitudes being six, ten, and eight, distances 30", p. 139°, and 96", p. 272°. In 12 Lyncis we find one of the most attractive of triplestars, which in good seeing weather is not beyond the powers of athree-inch glass, although we shall have a far more satisfactory view ofit with the four-inch. The components are of the sixth, seventh, andeighth magnitudes, distances 1. 4", p. 117°, and 8. 7", p. 304°. Amagnifying power which just suffices clearly to separate the disks ofthe two nearer stars makes this a fine sight. A beautiful contrast ofcolors belongs to the double star 14, but unfortunately the star is atpresent very close, the distance between its sixth and seventh magnitudecomponents not exceeding 0. 8", position angle 64°. Sigma 958 is a prettydouble, both stars being of the sixth magnitude, distance 5", p. 257°. Still finer is Sigma 1009, a double, whose stars are both a little abovethe seventh magnitude and nearly equal, distance 3", p. 156°. A lowpower suffices to show the three stars in 19, their magnitudes being sixand a half, seven and a half, and eight, distances 15", p. 312°, and215", p. 358°. Webb describes the two smaller stars as plum-colored. Plum-colored suns!

At the opposite end of the constellation are two fine doubles, Sigma1333, magnitudes six and a half and seven, distance 1. 4", p. 39°; and38, magnitudes four and seven, distance 2. 9", p. 235°. 

Under the guidance of map No. 6 we turn to Leo, which contains one ofthe leading gems among the double stars, gamma, whose components, of thesecond and fourth magnitudes, are respectively yellow and green, thegreen star, according to some observers, having a peculiar tinge of red. Their distance apart is 3. 7", p. 118°, and they are undoubtedly inrevolution about a common center, the probable period being about fourhundred years. The three-inch glass should separate them easily when theair is steady, and a pleasing sight they are. 

The star iota is a closer double, and also very pretty, magnitudes fourand eight, colors lemon and light blue, distance 2. 17", p. 53°. Otherdoubles are tau, magnitudes five and seven, distance 95", p. 170°; 88, magnitudes seven and nine, distance 15", p. 320°; 90, triple, magnitudessix, seven and a half, and ten, distance, 3. 5", p. 209°, and 59", p. 234°; 54, magnitudes four and a half and seven, distance 6. 2", p. 102°;and 49, magnitudes six and nine, distance 2. 4", p. 158°. 

Leo contains a remarkable variable star, R, deep red in color, andvarying in a space of a hundred and forty-four days from the fifth tothe tenth magnitude. It has also several nebulæ, of which only one needsspecial mention, No. 1861. This is spindle-shaped, and large telescopesshow that it consists of three nebulæ. The observer with ordinaryinstruments finds little to see and little to interest him in thesesmall, faint nebulæ. 

We may just glance at two double stars in the small constellation ofSextans, situated under Leo. These are: 9, magnitudes seven and eight, distance 53", p. 292°; and 35, magnitudes six and seven, distance 6. 9", p. 240°. 

[Illustration: MAP NO. 6. ]

Coma Berenices (map No. 6) includes several interesting objects. Letus begin with the star 2, a double, of magnitudes six and seven and ahalf, distance 3. 6", p. 240°. The color of the smaller star is lilac. This hue, although not extremely uncommon among double stars elsewhere, recurs again and again, with singular persistence, in this littleconstellation. For instance, in the very next star that we look at, 12, we find a double whose smaller component is _lilac_. The magnitudes in12 are five and eight, distance 66", p. 168°. So also the wide double17, magnitudes five and a half and six, distance 145", exhibits a tingeof _lilac_ in the smaller component; the triple 35, magnitudes five, eight, and nine, distances 1", p. 77°, and 28. 7", p. 124°, has fourcolors yellow, _lilac_, and blue, and the double 24, magnitudes five andsix, distance 20", p. 270°, combines an orange with a _lilac_ star, avery striking and beautiful contrast. We should make a mistake if weregarded this wonderful distribution of color among the double stars asaccidental. It is manifestly expressive of their physical condition, although we can not yet decipher its exact meaning. 

The binary 42 Comæ Berenicis is too close for ordinary telescopes, butit is highly interesting as an intermediate between those pairs whichthe telescope is able to separate and those--like beta Aurigæ--which nomagnifying power can divide, but which reveal the fact that they aredouble by the periodical splitting of their spectral lines. The orbit in42 Comæ Berenicis is a very small one, so that even when the componentsare at their greatest distance apart they can not be separated by afive-or six-inch glass. Burnham, using the Lick telescope, in 1890 madethe distance 0. 7"; Hall, using the Washington telescope, in 1891 made ita trifle more than 0. 5". He had measured it in 1886 as only 0. 27". Theperiod of revolution is believed to be about twenty-five years. 

In Coma Berenices there is an outlying field of the marvelous nebulousregion of Virgo, which we may explore on some future evening. But thenebulæ in Coma are very faint, and, for an amateur, hardly worth thetrouble required to pick them up. The two clusters included in the map, 2752 and 3453, are bright enough to repay inspection with our largestaperture. 

[Illustration: MAP NO. 7. ]

Although Hydra is the largest constellation in the heavens, extendingabout seven hours, or 105°, in right ascension, it containscomparatively few objects of interest, and most of these are in the heador western end of the constellation, which we examined during our firstnight at the telescope. In the central portion of Hydra, represented onmap No. 7, we find its leading star alpha, sometimes called Alphard, orCor Hydræ, a bright second-magnitude star that has been suspected ofvariability. It has a decided orange tint, and is accompanied, at adistance of 281", p. 153°, by a greenish tenth-magnitude star. Bu. 339is a fine double, magnitudes eight and nine and a half, distance 1. 3", p. 216°. The planetary nebula 2102 is about 1' in diameter, pale blue incolor, and worth looking at, because it is brighter than most objects ofits class. Tempel and Secchi have given wonderful descriptions of it, both finding multitudes of stars intermingled with nebulous matter. 

For a last glimpse at celestial splendors for the night, let us turn tothe rich cluster 1630, in Argo, just above the place where the stream ofthe Milky Way--here bright in mid-channel and shallowing toward theshores--separates into two or three currents before disappearing behindthe horizon. It is by no means as brilliant as some of the star clusterswe have seen, but it gains in beauty and impressiveness from thepresence of one bright star that seems to captain a host of inferiorluminaries. 

CHAPTER IV

VIRGO AND HER NEIGHBORS

 ... "that regionWhere still by night is seenThe Virgin goddess near to bright Boötes. "--POSTE'S ARATUS. 

[Illustration: MAP NO. 8. ]

Following the order of right ascension, we come next to the littleconstellations Crater and Corvus, which may be described as standing onthe curves of Hydra (map No. 8). Beginning with Crater, let us lookfirst at alpha, a yellow fourth-magnitude star, near which is acelebrated red variable R. With a low power we can see both alpha and Rin the same field of view, like a very wide double. There is a thirdstar of ninth magnitude, and bluish in color, near R on the side towardalpha. R is variable both in color and light. When reddest, it has beendescribed as "scarlet, " "crimson, " and "blood-colored"; when palest, itis a deep orange-red. Its light variation has a period the preciselength of which is not yet known. The cycle of change is includedbetween the eighth and ninth magnitudes. 

While our three-inch telescope suffices to show R, it is better to usethe five-inch, because of the faintness of the star. When the color iswell seen, the contrast with alpha is very pleasing. 

There is hardly anything else in Crater to interest us, and we pass overthe border into Corvus, and go at once to its chief attraction, the stardelta. The components of this beautiful double are of magnitudes threeand eight; distance 24", p. 211°; colors yellow and purple. 

The night being dark and clear, we take the five-inch and turn it on thenebula 3128, which the map shows just under the border of Corvus in theedge of Hydra. Herschel believed he had resolved this into stars. It isa faint object and small, not exceeding one eighth of the moon'sdiameter. 

Farther east in Hydra, as indicated near the left-hand edge of map No. 8, is a somewhat remarkable variable, R Hydræ. This star occasionallyreaches magnitude three and a half, while at minimum it is not muchabove the tenth magnitude. Its period is about four hundred andtwenty-five days. 

[Illustration: MAP NO. 9. ]

While we have been examining these comparatively barren regions, glad tofind one or two colored doubles to relieve the monotony of the search, aglittering white star has frequently drawn our eyes eastward and upward. It is Spica, the great gem of Virgo, and, yielding to its attraction, wenow enter the richer constellation over which it presides (map No. 9). Except for its beauty, which every one must admire, Spica, or alphaVirginis, has no special claim upon our attention. Some evidence hasbeen obtained that, like beta Aurigæ and Capella, it revolves with aninvisible companion of great mass in an orbit only six million miles indiameter. Spica's spectrum resembles that of Sirius. The faint starwhich our larger apertures show about 6' northeast of Spica is of thetenth magnitude. 

Sweeping westward, we come upon Sigma 1669, a pretty little double withnearly equal components of about the sixth magnitude, distance 5. 6", p. 124°. But our interest is not fully aroused until we reach gamma, a starwith a history. The components of this celebrated binary are bothnearly of the third magnitude, distance about 5. 8", p. 150°. Theyrevolve around their common center in something less than two hundredyears. According to some authorities, the period is one hundred andseventy years, but it is not yet certainly ascertained. It was noticedabout the beginning of the seventeenth century that gamma Virginis wasdouble. In 1836 the stars were so close together that no telescope thenin existence was able to separate them, although it is said that thedisk into which they had merged was elongated at Pulkowa. In a few yearsthey became easily separable once more. If theone-hundred-and-seventy-year period is correct, they should continue toget farther apart until about 1921. According to Asaph Hall, theirgreatest apparent distance is 6. 3", and their least apparent distance0. 5"; consequently, they will never again close up beyond the separatingpower of existing telescopes. 

There is a great charm in watching this pair of stars even with athree-inch telescope--not so much on account of what is seen, althoughthey are very beautiful, as on account of what we know they are doing. It is no slight thing to behold two distant stars obeying the law thatmakes a stone fall to the ground and compels the earth to swing roundthe sun. 

In theta we discover a fine triple, magnitudes four and a half, nine, and ten; distances 7", p. 345°, and 65", p. 295°. The ninth-magnitudestar has been described as "violet, " but such designations of color areoften misleading when the star is very faint. On the other hand itshould not be assumed that a certain color does not exist because theobserver can not perceive it, for experience shows that there is a widedifference among observers in the power of the eye to distinguish color. I have known persons who could not perceive the difference of hue insome of the most beautifully contrasted colored doubles to be found inthe sky. I am acquainted with an astronomer of long experience in theuse of telescopes, whose eye is so deficient in color sense that hedenies that there are any decided colors among the stars. Such personsmiss one of the finest pleasures of the telescope. In examining thetaVirginis we shall do best to use our largest aperture, viz. , thefive-inch. Yet Webb records that all three of the stars in this triplehave been seen with a telescope of only three inches aperture. Theamateur must remember in such cases how much depends upon practice aswell as upon the condition of the atmosphere. There are lamentably fewnights in a year when even the best telescope is ideally perfect inperformance, but every night's observation increases the capacity of theeye, begetting a kind of critical judgment which renders it to someextent independent of atmospheric vagaries. It will also be found thatthe idiosyncrasies of the observer are reflected in his instrument, which seems to have its fits of excellence, its inspirations so tospeak, while at other times it behaves as if all its wonderful powershad departed. 

Another double that perhaps we had better not try with less than fourinches aperture is 84 Virginis. The magnitudes are six and nine;distance, 3. 5", p. 233°. Colors yellow and blue. Sigma 1846 is afifth-magnitude star with a tenth-magnitude companion, distance only 4", p. 108°. Use the five-inch. 

And now we approach something that is truly marvelous, the "Field of theNebulæ. " This strange region, lying mostly in the constellation Virgo, is roughly outlined by the stars beta, eta, gamma, delta, and epsilon, which form two sides of a square some 15° across. It extends, however, for some distance into Coma Berenices, while outlying nebulæ belongingto it are also to be found in the eastern part of Leo. Unfortunatelyfor those who expect only brilliant revelations when they look through atelescope, this throng of nebulæ consists of small and inconspicuouswisps as ill defined as bits of thistle-down floating high in the air. There are more than three hundred of them all told, but even thebrightest are faint objects when seen with the largest of ourtelescopes. Why do they congregate thus? That is the question whichlends an interest to the assemblage that no individual member of itcould alone command. It is a mystery, but beyond question it isexplicable. The explanation, however, is yet to be discovered. 

The places of only three of the nebulæ are indicated on the map. No. 2806 has been described as resembling in shape a shuttle. Its length isnearly one third of the moon's diameter. It is brightest near thecenter, and has several faint companions. No. 2961 is round, 4' indiameter, and is accompanied by another round nebula in the same fieldof view toward the south. No. 3105 is double, and powerful telescopesshow two more ghostly companions. There is an opportunity for good anduseful work in a careful study of the little nebulæ that swim into viewall over this part of Virgo. Celestial photography has triumphs in storefor itself here. 

Scattered over and around the region where the nebulæ are thickest wefind eight or nine variable stars, three of the most remarkable ofwhich, R, S, and U, may be found on the map. R is very irregular, sometimes attaining magnitude six and a half, while at other times itsmaximum brightness does not exceed that of an eighth-magnitude star. Atminimum it sinks to the tenth or eleventh magnitude. Its period is onehundred and forty-five days. U varies from magnitude seven or eight downto magnitude twelve or under and then regains its light, in a period ofabout two hundred and seven days. S is interesting for its brilliant redcolor. When brightest, it exceeds the sixth magnitude, but at some ofits maxima the magnitude is hardly greater than the eighth. At minimumit goes below the twelfth magnitude. Period, three hundred andseventy-six days. 

[Illustration: MAP NO. 10. ]

Next east of Virgo is Libra, which contains a few notable objects (mapNo. 10). The star alpha has a fifth-magnitude companion, distant about230", which can be easily seen with an opera glass. At the point markedA on the map is a curious multiple star, sometimes referred to by itsnumber in Piazzi's catalogues as follows: 212 P. Xiv. The two principalstars are easily seen, their magnitudes being six and seven and a half;distance 15", p. 290°. Burnham found four other faint companions, forwhich it would be useless for us to look. The remarkable thing is thatthese faint stars, the nearest of which is distant about 50" from thelargest member of the group and the farthest about 129", do not share, according to their discoverer, in the rapid proper motion of the twomain stars. 

In iota we find a double a little difficult for our three-inch. Thecomponents are of magnitudes four and a half and nine, distance 57", p. 110°. Burnham discovered that the ninth-magnitude star consists of twoof the tenth less than 2" apart, p. 24°. 

No astronomer who happens to be engaged in this part of the sky everfails, unless his attention is absorbed by something of specialinterest, to glance at beta Libræ, which is famous as the only naked-eyestar having a decided green color. The hue is pale, but manifest. [3]

[3] Is the slight green tint perceptible in Sirius variable? I amsometimes disposed to think it is. 

The star is a remarkable variable, belonging to what is called the Algoltype. Its period, according to Chandler, is 2 days 7 hours, 51minutes, 22. 8 seconds. The time occupied by the actual changes is abouttwelve hours. At maximum the star is of magnitude five and at minimum ofmagnitude 6. 2. 

[Illustration: MAP NO. 11. ]

We may now conveniently turn northward from Virgo in order to exploreBoötes, one of the most interesting of the constellations (map No. 11). Its leading star alpha, Arcturus, is the brightest in the northernhemisphere. Its precedence over its rivals Vega and Capella, long indispute, has been settled by the Harvard photometry. You notice that thecolor of Arcturus, when it has not risen far above the horizon, is ayellowish red, but when the star is near mid-heaven the color fades tolight yellow. The hue is possibly variable, for it is recorded that in1852 Arcturus appeared to have nearly lost its color. If it shouldeventually turn white, the fact would have an important bearing upon thequestion whether Sirius was, as alleged, once a red or flame-coloredstar. 

But let us sit here in the starlight, for the night is balmy, and talkabout Arcturus, which is perhaps actually the greatest sun within therange of terrestrial vision. Its parallax is so minute that theconsideration of the tremendous size of this star is a thing that theimagination can not placidly approach. Calculations, based on itsassumed distance, which show that it _outshines the sun several thousandtimes_, may be no exaggeration of the truth! It is easy to make such acalculation. One of Dr. Elkin's parallaxes for Arcturus is 0. 018". Thatis to say, the displacement of Arcturus due to the change in theobserver's point of view when he looks at the star first from one sideand then from the other side of the earth's orbit, 186, 000, 000 milesacross, amounts to only eighteen one-thousandths of a second of arc. Wecan appreciate how small that is when we reflect that it is about equalto the apparent distance between the heads of two pins placed an inchapart and viewed from a distance of a hundred and eighty miles!

Assuming this estimate of the parallax of Arcturus, let us see how itwill enable us to calculate the probable size or light-giving power ofthe star as compared with the sun. The first thing to do is to multiplythe earth's distance from the sun, which may be taken at 93, 000, 000miles, by 206, 265, the number of seconds of arc in a radian, the base ofcircular measure, and then divide the product by the parallax of thestar. Performing the multiplication and division, we get the following:

19, 182, 645, 000, 000 / . 018 = 1, 065, 702, 500, 000, 000. 

The quotient represents miles! Call it, in round numbers, a thousandmillions of millions of miles. This is about 11, 400, 000 times thedistance from the earth to the sun. 

Now for the second part of the calculation: The amount of light receivedon the earth from some of the brighter stars has been experimentallycompared with the amount received from the sun. The results differrather widely, but in the case of Arcturus the ratio of the star's lightto sunlight may be taken as about one twenty-five-thousand-millionth--i. E. , 25, 000, 000, 000 stars, each equal to Arcturus, would together shedupon the earth as much light as the sun does. But we know that lightvaries inversely as the square of the distance; for instance, if the sunwere twice as far away as it is, its light would be diminished for us toa quarter of its present amount. Suppose, then, that we could remove theearth to a point midway between the sun and Arcturus, we should then be5, 700, 000 times as far from the sun as we now are. In order to estimatehow much light the sun would send us from that distance we must squarethe number 5, 700, 000 and then take the result inversely, or as afraction. We thus get 1 / 32, 490, 000, 000, 000, representing the ratio ofthe sun's light at half the distance of Arcturus to that at its realdistance. But while receding from the sun we should be approachingArcturus. We should get, in fact, twice as near to that star as we werebefore, and therefore its light would be increased for us fourfold. Now, if the amount of sunlight had not changed, it would exceed the light ofArcturus only a quarter as much as it did before, or in the ratio of25, 000, 000, 000 / 4 = 6, 250, 000, 000 to 1. But, as we have seen, thesunlight would diminish through increase of distance to one32, 490, 000, 000, 000th part of its original amount. Hence its alteredratio to the light of Arcturus would become 6, 250, 000, 000 to32, 490, 000, 000, 000, or 1 to 5, 198. 

This means that if the earth were situated midway between the sun andArcturus, it would receive 5, 198 times as much light from that star asit would from the sun! It is quite probable, moreover, that the heat ofArcturus exceeds the solar heat in the same ratio, for the spectroscopeshows that although Arcturus is surrounded with a cloak of metallicvapors proportionately far more extensive than the sun's, yet, smotheredas the great star seems in some respects to be, it rivals Sirius itselfin the intensity of its radiant energy. 

If we suppose the radiation of Arcturus to be the same per unit ofsurface as the sun's, it follows that Arcturus exceeds the sun about375, 000 times in volume, and that its diameter is no less than62, 350, 000 miles! Imagine the earth and the other planets constitutingthe solar system removed to Arcturus and set revolving around it inorbits of the same forms and sizes as those in which they circle aboutthe sun. Poor Mercury! For that little planet it would indeed be a jumpfrom the frying pan into the fire, because, as it rushed to perihelion, Mercury would plunge more than 2, 500, 000 miles beneath the surface ofthe giant star. Venus and the earth would melt like snowflakes at themouth of a furnace. Even far-away Neptune, the remotest member of thesystem, would swelter in torrid heat. 

But stop! Look at the sky. Observe how small and motionless the disks ofthe stars have become. Back to the telescopes at once, for this is atoken that the atmosphere is steady, and that "good seeing" may beexpected. It is fortunate, for we have some delicate work before us. Thevery first double star we try in Boötes, Sigma 1772, requires the use ofthe four-inch, and the five-inch shows it more satisfactorily. Themagnitudes are sixth and ninth, distance 5", p. 140°. On the other sideof Arcturus we find zeta, a star that we should have had no greatdifficulty in separating thirty years ago, but which has now closed upbeyond the reach even of our five-inch. The magnitudes are both fourth, and the distance less than a quarter of a second; position anglechanging. It is apparently a binary, and if so will some time widenagain, but its period is unknown. The star 279, also known as Sigma1910, near the southeastern edge of the constellation, is a prettydouble, each component being of the seventh magnitude, distance 4", p. 212°. Just above zeta we come upon pi, an easy double for thethree-inch, magnitudes four and six, distance 6" p. 99°. Next is xi, ayellow and purple pair, whose magnitudes are respectively five andseven, distance less than 3", p. 200°. This is undoubtedly a binary witha period of revolution of about a hundred and thirty years. Its distancedecreased about 1" between 1881 and 1891. It was still decreasing in1899, when it had become 2. 5". The orbital swing is also very apparentin the change of the position angle. 

The telescopic gem of Boötes, and one of "the flowers of the sky, " isepsilon, also known as Mirac. When well seen, as we shall see itto-night, epsilon Boötis is superb. The magnitudes of its two componentstars are two and a half (according to Hall, three) and six. Thedistance is about 2. 8", p. 326°. The contrast of colors--bright orangeyellow, set against brilliant emerald green--is magnificent. There arevery few doubles that can be compared with it in this respect. Thethree-inch will separate it, but the five-inch enables us best to enjoyits beauty. It appears to be a binary, but the motion is very slow, andnothing certain is yet known of its period. 

In delta we have a very wide and easy double; magnitudes three and ahalf and eight and a half, distance 110", p. 75°. The smaller star has alilac hue. We can not hope with any of our instruments to see all of thethree stars contained in, but two of them are easily seen; magnitudesfour and seven, distance 108", p. 172°. The smaller star is againdouble; magnitudes seven and eight, distance 0. 77", p. 88°. It isclearly a binary, with a long period. A six-inch telescope that couldseparate this star at present would be indeed a treasure. Sigma 1926 isanother object rather beyond our powers, on account of the contrast ofmagnitudes. These are six and eight and a half; distance 1. 3", p. 256°. 

Other doubles are: 44 (Sigma 1909), magnitudes five and six, distance4. 8", p. 240°; 39 (Sigma 1890), magnitudes both nearly six, distance3. 6", p. 45°. Smaller star light red; iota, magnitudes four and a halfand seven and a half, distance 38", p. 33°; kappa, magnitudes five and ahalf and eight, distance 12. 7", p. 238°. Some observers see a greenishtinge in the light of the larger star, the smaller one being blue. 

There are one or two interesting things to be seen in that part of CanesVenatici which is represented on map No. 11. The first of these is thestar cluster 3936. This will reward a good look with the five-inch. Withlarge telescopes as many as one thousand stars have been discernedpacked within its globular outlines. 

The star 25 (Sigma 1768) is a close binary with a period estimated atone hundred and twenty-five years. The magnitudes are six and seven oreight, distance about 1", p. 137°. We may try for this with thefive-inch, and if we do not succeed in separating the stars we may hopeto do so some time, for the distance between them is increasing. 

Although the nebula 3572 is a very wonderful object, we shall leave itfor another evening. 

Eastward from Boötes shines the circlet of Corona Borealis, whose formis so strikingly marked out by the stars that the most careless eyeperceives it at once. Although a very small constellation, it aboundswith interesting objects. We begin our attack with the five-inch onSigma 1932, but not too confident that we shall come off victors, forthis binary has been slowly closing for many years. The magnitudes aresix and a half and seven, distance 0. 84", p. 150°. Not far distant isanother binary, at present beyond our powers, eta. Here the magnitudesare both six, distance 0. 65", p. 3°. Hall assigns a period of fortyyears to this star. 

The assemblage of close binaries in this neighborhood is very curious. Only a few degrees away we find one that is still more remarkable, thestar gamma. What has previously been said about 42 Comæ Berenicisapplies in a measure to this star also. It, too, has a comparativelysmall orbit, and its components are never seen widely separated. In 1826their distance was 0. 7"; in 1880 they could not be split; in 1891 thedistance had increased to 0. 36", and in 1894 it had become 0. 53", p. 123°. But in 1899 Lewis made the distance only 0. 43". The period hasbeen estimated at one hundred years. 

While the group of double stars in the southern part of Corona Borealisconsists, as we have seen, of remarkably close binaries, another groupin the northern part of the same constellation comprises stars that areeasily separated. Let us first try zeta. The powers of the three-inchare amply sufficient in this case. The magnitudes are four and five, distance 6. 3", p. 300°. Colors, white or bluish-white and blue or green. 

Next take sigma, whose magnitudes are five and six, distance 4", p. 206°. With the five-inch we may look for a second companion of the tenthmagnitude, distance 54", p. 88°. It is thought highly probable thatsigma is a binary, but its period has simply been guessed at. 

Finally, we come to nu, which consists of two very widely separatedstars, nu^1 and nu^2, each of which has a faint companion. With thefive-inch we may be able to see the companion of nu^2, the moresoutherly of the pair. The magnitude of the companion is variously givenas tenth and twelfth, distance 137", p. 18°. 

With the aid of the map we find the position of the new star of 1866, which is famous as the first so-called temporary star to whichspectroscopic analysis was applied. When first noticed, on May 12, 1866, this star was of the second magnitude, fully equaling in brilliancyalpha, the brightest star of the constellation; but in about two weeksit fell to the ninth magnitude. Huggins and Miller eagerly studied thestar with the spectroscope, and their results were received with deepestinterest. They concluded that the light of the new star had twodifferent sources, each giving a spectrum peculiar to itself. One of thespectra had dark lines and the other bright lines. It will beremembered that a similar peculiarity was exhibited by the new star inAuriga in 1893. But the star in Corona did not disappear. It diminishedto magnitude nine and a half or ten, and stopped there; and it is stillvisible. In fact, subsequent examination proved that it had beencatalogued at Bonn as a star of magnitude nine and a half in 1855. Consequently this "blaze star" of 1866 will bear watching in itsdecrepitude. Nobody knows but that it may blaze again. Perhaps it is asun-like body; perhaps it bears little resemblance to a sun as weunderstand such a thing. But whatever it may be, it has proved itselfcapable of doing very extraordinary things. 

We have no reason to suspect the sun of any latent eccentricities, likethose that have been displayed by "temporary" stars; yet, acting on theprinciple which led the old emperor-astrologer Rudolph II to torment hismind with self-made horoscopes of evil import, let us unscientificallyimagine that the sun _could_ suddenly burst out with several hundredtimes its ordinary amount of heat and light, thereby putting us into aproper condition for spectroscopic examination by curious astronomers indistant worlds. 

But no, after all, it is far pleasanter to keep within the strictboundaries of science, and not imagine anything of the kind. 

CHAPTER V

IN SUMMER STAR-LANDS

"I heard the trailing garments of the night Sweep through her marble halls, I saw her sable skirts all fringed with light From the celestial walls. "--H. W. LONGFELLOW. 

In the soft air of a summer night, when fireflies are flashing theirlanterns over the fields, the stars do not sparkle and blaze like thosethat pierce the frosty skies of winter. The light of Sirius, Aldebaran, Rigel, and other midwinter brilliants possesses a certain gemlikehardness and cutting quality, but Antares and Vega, the great summerstars, and Arcturus, when he hangs westering in a July night, exhibit amilder radiance, harmonizing with the character of the season. Thisdifference is, of course, atmospheric in origin, although it may bepartly subjective, depending upon the mental influences of the mutationsof Nature. 

[Illustration: MAP NO. 12. ]

The constellation Scorpio is nearly as striking in outline as Orion, andits brightest star, the red Antares (alpha in map No. 12), carriesconcealed in its rays a green jewel which, to the eye of the enthusiastin telescopic recreation, appears more beautiful and inviting each timethat he penetrates to its hiding place. 

We shall begin our night's work with this object, and the four-inchglass will serve our purpose, although the untrained observer would bemore certain of success with the five-inch. A friend of mine has seenthe companion of Antares with a three-inch, but I have never tried thestar with so small an aperture. When the air is steady and the companioncan be well viewed, there is no finer sight among the double stars. Thecontrast of colors is beautifully distinct--fire-red and bright green. The little green star has been seen emerging from behind the moon, aheadof its ruddy companion. The magnitudes are one and seven and a half oreight, distance 3", p. 270°. Antares is probably a binary, although itsbinary character has not yet been established. 

A slight turn of the telescope tube brings us to the star sigma, a widedouble, the smaller component of which is blue or plum-colored;magnitudes four and nine, distance 20", p. 272°. From sigma we pass tobeta, a very beautiful object, of which the three-inch gives us asplendid view. Its two components are of magnitudes two and six, distance 13", p. 30°; colors, white and bluish. It is interesting toknow that the larger star is itself double, although none of thetelescopes we are using can split it. Burnham discovered that it has atenth-magnitude companion; distance less than 1", p. 87°. 

And now for a triple, which will probably require the use of our largestglass. Up near the end of the northern prolongation of the constellationwe perceive the star xi. The three-inch shows us that it is double; thefive-inch divides the larger star again. The magnitudes are respectivelyfive, five and a half, and seven and a half, distances 0. 94", p. 215°, and 7", p. 70°. 

A still more remarkable star, although one of its components is beyondour reach, is nu. With the slightest magnifying this object splits upinto two stars, of magnitudes four and seven, situated rather more than40" apart. A high power divides the seventh-magnitude companion intotwo, each of magnitude six and a half, distance 1. 8", p. 42°. But (andthis was another of Burnham's discoveries) the fourth-magnitude staritself is double, distance 0. 8", p. About 0°. The companion in this caseis of magnitude five and a half. 

Next we shall need a rather low-power eyepiece and our largest aperturein order to examine a star cluster, No. 4173, which was especiallyadmired by Sir William Herschel, who discovered that it was not, asMessier had supposed, a circular nebula. Herschel regarded it as therichest mass of stars in the firmament, but with a small telescope itappears merely as a filmy speck that has sometimes been mistaken for acomet. In 1860 a new star, between the sixth and seventh magnitude inbrilliance, suddenly appeared directly in or upon the cluster, and thefeeble radiance of the latter was almost extinguished by the superiorlight of the stranger. The latter disappeared in less than a month, andhas not been seen again, although it is suspected to be a variable, and, as such, has been designated with the letter T. Two other knownvariables, both very faint, exist in the immediate neighborhood. According to the opinion that was formerly looked upon with favor, thevariable T, if it is a variable, simply lies in the line of sightbetween the earth and the star cluster, and has no actual connectionwith the latter. But this opinion may not, after all, be correct, forMr. Bailey's observations show that variable stars sometimes exist inlarge numbers in clusters, although the variables thus observed are ofshort period. The cluster 4183, just west of Antares, is also worth aglance with the five-inch glass. It is dense, but its stars are verysmall, so that to enjoy its beauty we should have to employ a largetelescope. Yet there is a certain attraction in these far-away glimpsesof starry swarms, for they give us some perception of the awfulprofundity of space. When the mind is rightly attuned for theserevelations of the telescope, there are no words that can express itsimpressions of the overwhelming perspective of the universe. 

The southern part of the constellation Ophiuchus is almost inextricablymingled with Scorpio. We shall, therefore, look next at its attractions, beginning with the remarkable array of star clusters 4264, 4268, 4269, and 4270. All of these are small, 2' or 3' in diameter, and globular inshape. No. 4264 is the largest, and we can see some of the starscomposing it. But these clusters, like those just described in Scorpio, are more interesting for what they signify than for what they show; andthe interest is not diminished by the fact that their meaning is more orless of a mystery. Whether they are composed of pygmy suns or of greatsolar globes like that one which makes daylight for the earth, theirassociation in spherical groups is equally suggestive. 

There are two other star clusters in Ophiuchus, and within the limits ofmap No. 12, both of which are more extensive than those we have justbeen looking at. No. 4211 is 5' or 6' in diameter, also globular, brighter at the center, and surrounded by several comparativelyconspicuous stars. No. 4346 is still larger, about half as broad as themoon, and many of its scattered stars are of not less than the ninthmagnitude. With a low magnifying power the field of view surrounding thecluster appears powdered with stars. 

There are only two noteworthy doubles in that part of Ophiuchus withwhich we are at present concerned: 36, whose magnitudes are five andseven, distance 4. 3", p. 195°, colors yellow and red; and 39, magnitudessix and seven and a half, distance 12", p. 356°, colors yellow ororange and blue. The first named is a binary whose period has not beendefinitely ascertained. 

The variable R has a period a little less than three hundred and threedays. At its brightest it is of magnitude seven or eight, and at minimumit diminishes to about the twelfth magnitude. 

The spot where the new star of 1604 appeared is indicated on the map. This was, with the exception of Tycho's star in 1572, the brightesttemporary star of which we possess a trustworthy account. It isfrequently referred to as Kepler's star, because Kepler watched it withconsiderable attention, but unfortunately he was not as good an observeras Tycho was. The star was first seen on October 10, 1604, and was thenbrighter than Jupiter. It did not, however, equal Venus. It graduallyfaded and in March, 1606, disappeared. About twelve degrees northwest ofthe place of the star of 1604, and in that part of the constellationSerpens which is included in map No. 12, we find the location of anothertemporary star, that of 1848. It was first noticed by Mr. Hind on April28th of that year, when its magnitude was not much above the seventh, and its color was red. It brightened rapidly, until on May 2d it was ofmagnitude three and a half. Then it began to fade, but very slowly, andit has never entirely disappeared. It is now of the twelfth orthirteenth magnitude. 

In passing we may glance with a low power at nu Serpentis, a widedouble, magnitudes four and nine, distance 50", p. 31°, colorscontrasted but uncertain. 

Sagittarius and its neighbor, the small but rich constellation ScutumSobieskii, attract us next. We shall first deal with the westernportions of these constellations which are represented on Map No. 12. The star in Sagittarius is a wide triple, magnitudes three and a half, nine and a half, and ten, distances 40", p. 315°, and 45", p. 114°. Butthe chief glory of Sagittarius (and the same statement applies to ScutumSobieskii) lies in its assemblage of star clusters. One of these, No. 4361, also known as M 8, is plainly visible to the naked eye as a brightspot in the Milky Way. We turn our five-inch telescope, armed with a lowmagnifying power, upon this subject and enjoy a rare spectacle. As weallow it to drift through the field we see a group of threecomparatively brilliant stars advancing at the front of a wonderfultrain of mingled star clusters and nebulous clouds. A little northwestof it appears the celebrated trifid nebula, No. 4355 on the map. Thereis some evidence that changes have occurred in this nebula since itsdiscovery in the last century. Barnard has made a beautiful photographshowing M 8 and the trifid nebula on the same plate, and he remarks thatthe former is a far more remarkable object than its more famousneighbor. Near the eastern border of the principal nebulous cloud thereis a small and very black hole with a star poised on its eastern edge. This hole and the star are clearly shown in the photograph. 

Cluster No. 4397 (M 24) is usually described as resembling, to the nakedeye, a protuberance on the edge of the Milky Way. It is nearly threetimes as broad as the moon, and is very rich in minute stars, which areat just such a degree of visibility that crowds of them continuallyappear and disappear while the eye wanders over the field, just as facesare seen and lost in a vast assemblage of people. This kind of luminousagitation is not peculiar to M 24, although that cluster exhibits itbetter than most others do on account of both the multitude and theminuteness of its stars. 

A slight sweep eastward brings us to yet another meeting place of stars, the cluster M 25, situated between the variables U and V. This isbrilliant and easily resolved into its components, which include anumber of double stars. 

The two neighboring variables just referred to are interesting. U has aperiod of about six days and three quarters, and its range of magnituderuns from the seventh down to below the eighth. V is a somewhatmysterious star. Chandler removed it from his catalogue of variablesbecause no change had been observed in its light by either himself, Sawyer, or Yendell. Quirling, the discoverer of its variability, gavethe range as between magnitudes 7. 6 and 8. 8. It must, therefore, beexceedingly erratic in its changes, resembling rather the temporarystars than the true variables. 

In that part of Scutum Sobieskii contained in map No. 12 we find aninteresting double, Sigma 2325, whose magnitudes are six and nine, distance 12. 3", p. 260°, colors white and orange. Sigma 2306 is atriple, magnitudes seven, eight, and nine, distances 12", p. 220°, and0. 8", p. 68°. The third star is, however, beyond our reach. The colorsof the two larger are respectively yellow and violet. 

The star cluster 4400 is about one quarter as broad as the moon, andeasily seen with our smallest aperture. 

[Illustration: MAP NO. 13. ]

Passing near to the region covered by map No. 13, we find the remainingportions of the constellations Sagittarius and Scutum Sobieskii. It willbe advisable to finish with the latter first. Glance at the clusters4426 and 4437. Neither is large, but both are rich in stars. The nebula4441 is a fine object of its kind. It brightens toward the center, andHerschel thought he had resolved it into stars. The variable R isremarkable for its eccentricities. Sometimes it attains nearly thefourth magnitude, although usually at maximum it is below the fifth, while at minimum it is occasionally of the sixth and at other times ofthe seventh or eighth magnitude. Its period is irregular. 

Turning back to Sagittarius, we resume our search for interestingobjects there, and the first that we discover is another star cluster, for the stars are wonderfully gregarious in this quarter of the heavens. The number our cluster bears on the map is 4424, corresponding with M 22in Messier's catalogue. It is very bright, containing many stars of thetenth and eleventh magnitudes, as well as a swarm of smaller ones. SirJohn Herschel regarded the larger stars in this cluster as possessing areddish tint. Possibly there was some peculiarity in his eye that gavehim this impression, for he has described a cluster in the constellationToucan in the southern hemisphere as containing a globular mass ofrose-colored stars inclosed in a spherical shell of white stars. Laterobservers have confirmed his description of the shape and richness ofthis cluster in Toucan, but have been unable to perceive the red hue ofthe interior stars. 

The eastern expanse of Sagittarius is a poor region compared with thewestern end of the constellation, where the wide stream of the Milky Waylike a great river enriches its surroundings. The variables T and R areof little interest to us, for they never become bright enough to be seenwithout the aid of a telescope. In 54 we find, however, an interestingdouble, which with larger telescopes than any of ours appears as atriple. The two stars that we see are of magnitudes six and seven and ahalf, distance 45", p. 42°, colors yellow and blue. The third star, perhaps of thirteenth magnitude, is distant 36", p. 245°. 

Retaining map No. 13 as our guide, we examine the western part of theconstellation Capricornus. Its leader alpha is a naked-eye double, thetwo stars being a little more than 6' apart. Their magnitudes are threeand four, and both have a yellowish hue. The western star is alpha^1, and is the fainter of the two. The other is designated as alpha^2. Bothare double. The components of alpha^1 are of magnitudes four and eightand a half, distance 44", p. 220°. With the Washington twenty-six-inchtelescope a third star of magnitude fourteen has been found at adistance of 40", p. 182°. In alpha^2 the magnitudes of the componentsare three and ten and a half, distance 7. 4", p. 150°. The smaller starhas a companion of the twelfth or thirteenth magnitude, distance 1. 2", p. 240°. This, of course, is hopelessly beyond our reach. Yet anotherstar of magnitude nine, distance 154", p. 156, we may see easily. 

Dropping down to beta, we find it to be a most beautiful and easydouble, possessing finely contrasted colors, gold and blue. The largerstar is of magnitude three, and the smaller, the blue one, of magnitudesix, distance 205", p. 267°. Between them there is a very faint starwhich larger telescopes than ours divide into two, each of magnitudeeleven and a half; separated 3", p. 325°. 

Still farther south and nearly in a line drawn from alpha through betawe find a remarkable group of double stars, sigma, pi, rho, and omicron. The last three form a beautiful little triangle. We begin with sigma, the faintest of the four. The magnitudes of its components are six andnine, distance 54", p. 177°. In pi the magnitudes are five and nine, distance 3. 4", p. 145°; in rho, magnitudes five and eight, distance3. 8", p. 177° (a third star of magnitude seven and a half is seen at adistance of 4', p. 150°); in omicron, magnitudes six and seven, distance22", p. 240°. 

The star cluster 4608 is small, yet, on a moonless night, worth a glancewith the five-inch. 

[Illustration: MAP NO. 14. ]

We now pass northward to the region covered by map No. 14, including theremainder of Ophiuchus and Serpens. Beginning with the head of Serpens, in the upper right-hand corner of the map, we find that beta, ofmagnitude three and a half, has a ninth-magnitude companion, distance30", p. 265°. The larger star is light blue and the smaller oneyellowish. The little star nu is double, magnitudes five and nine, distance 50", p. 31°, colors contrasted but uncertain. In delta we finda closer double, magnitudes three and four, distance 3. 5", p. 190°. Itis a beautiful object for the three-inch. The leader of theconstellation, alpha, of magnitude two and a half, has a faint companionof only the twelfth magnitude, distance 60", p. 350°. The small star isbluish. The variable R has a period about a week short of one year, andat maximum exceeds the sixth magnitude, although sinking at minimum toless than the eleventh. Its color is ruddy. 

Passing eastward, we turn again into Ophiuchus, and find immediately thevery interesting double, lambda, whose components are of magnitudes fourand six, distance 1", p. 55°. This is a long-period binary, andnotwithstanding the closeness of its stars, our four-inch shouldseparate them when the seeing is fine. We shall do better, however, totry with the five-inch. Sigma 2166 consists of two stars of magnitudessix and seven and a half, distance 27", p. 280°. Sigma 2173 is a doubleof quite a different order. The magnitudes of its components are bothsix, the distance in 1899 0. 98", p. 331°. It is evidently a binary inrapid motion, as the distance changed from about a quarter of a secondin 1881 to more than a second in 1894. The star tau is a fine triple, magnitudes five, six, and nine, distances 1. 8", p. 254°, and 100", p. 127°. The close pair is a binary system with a long period ofrevolution, estimated at about two hundred years. We discover anothergroup of remarkable doubles in 67, 70, and 73. In the first-named starthe magnitudes are four and eight, distance 55", p. 144°, colorsfinely contrasted, pale yellow and red. 

Much more interesting, however, is 70, a binary whose components havecompleted a revolution since their discovery by Sir William Herschel, the period being ninety-five years. The magnitudes are four and six, or, according to Hall, five and six, distance in 1894 2. 3"; in 1900, 1. 45", according to Maw. Hall says the apparent distance when the stars areclosest is about 1. 7", and when they are widest 6. 7". This star is oneof those whose parallax has been calculated with a reasonable degree ofaccuracy. Its distance from us is about 1, 260, 000 times the distance ofthe sun, the average distance apart of the two stars is about2, 800, 000, 000 miles (equal to the distance of Neptune from the sun), andtheir combined mass is three times that of the sun. Hall has seen in thesystem of 70 Ophiuchi three stars of the thirteenth magnitude or less, at distances of about 60", 90", and 165" respectively. 

The star 73 is also a close double, and beyond our reach. Its magnitudesare six and seven, distance 0. 7", p. 245°. It is, no doubt, a binary. 

Three star clusters in Ophiuchus remain to be examined. The first ofthese, No. 4256, is partially resolved into stars by the five-inch. No. 4315 is globular, and has a striking environment of bystanding stars. Itis about one quarter as broad as the full moon, and our largest aperturereveals the faint coruscation of its crowded components. No. 4410 is acoarser and more scattered star swarm--a fine sight!

Farther toward the east we encounter a part of Serpens again, whichcontains just one object worth glancing at, the double theta, whosestars are of magnitudes four and four and a half, distance 21", p. 104°. Color, both yellow, the smaller star having the deeper hue. 

[Illustration: MAP NO. 15. ]

Let us next, with the guidance of map No. 15, enter the rich star fieldsof Hercules, and of the head and first coils of Draco. According toArgelander, Hercules contains more stars visible to the naked eye thanany other constellation, and he makes the number of them one hundred andfifty-five, nearly two thirds of which are only of the sixth magnitude. But Heis, who saw more naked-eye stars than Argelander, makes Ursa Majorprecisely equal to Hercules in the number of stars, his enumerationshowing two hundred and twenty-seven in each constellation, while, according to him, Draco follows very closely after, with two hundred andtwenty stars. Yet, on account of the minuteness of the majority of theirstars, neither of these constellations makes by any means as brilliant adisplay as does Orion, to which Argelander assigns only one hundred andfifteen naked-eye stars, and Heis one hundred and thirty-six. 

We begin in Hercules with the star kappa, a pretty little double ofmagnitudes five and a half and seven, distance 31", p. 10°, colorsyellow and red. Not far away we find, in gamma, a larger star with afainter companion, the magnitudes in this case being three and a halfand nine, distance 38", p. 242°, colors white and faint blue or lilac. One of the most beautiful of double stars is alpha Herculis. Themagnitudes are three and six, distance 4. 7", p. 118°, colors orange andgreen, very distinct. Variability has been ascribed to each of the starsin turn. It is not known that they constitute a binary system, becauseno certain evidence of motion has been obtained. Another very beautifuland easily separated double is delta, magnitudes three and eight, distance 19", p. 175°, colors pale green and purple. 

Sweeping northwestward to zeta, we encounter a celebrated binary, toseparate which at present requires the higher powers of a six-inchglass. The magnitudes are three and six and a half, distance in 1899, 0. 6", p. 264°; in 1900, 0. 8", p. 239°. The period of revolution isthirty-five years, and two complete revolutions have been observed. Theapparent distance changes from 0. 6" to 1. 6". They were at their extremedistance in 1884. 

Two pleasing little doubles are Sigma 2101, magnitudes six and nine, distance 4", p. 57°, and Sigma 2104, magnitudes six and eight, distance6", p. 20°. At the northern end of the constellation is 42, a doublethat requires the light-grasping power of our largest glass. Itsmagnitudes are six and twelve, distance 20", p. 94°. In rho we discoveranother distinctly colored double, both stars being greenish or bluish, with a difference of tone. The magnitudes are four and five and a half, distance 3. 7", p. 309°. But the double 95 is yet more remarkable for thecolors of its stars. Their magnitudes are five and five and a half, distance 6", p. 262°, colors, according to Webb, "light apple-green andcherry-red. " But other observers have noted different hues, one callingthem both golden yellow. I think Webb's description is more nearlycorrect. Sigma 2215 is a very close double, requiring larger telescopesthan those we are working with. Its magnitudes are six and a half andeight, distance 0. 7", p. 300°. It is probably a binary. Sigma 2289 isalso close, but our five-inch will separate it: magnitudes six andseven, distance 1. 2", p. 230°. 

Turning to, we have to deal with a triple, one of whose stars is atpresent beyond the reach of our instruments. The magnitudes of the twothat we see are four and ten, distance 31", p. 243°. The tenth-magnitudestar is a binary of short period (probably less than fifty years), thedistance of whose components was 2" in 1859, 1" in 1880, 0. 34" in 1889, and 0. 54" in 1891, when the position angle was 25°, and rapidlyincreasing. The distance is still much less than 1". 

For a glance at a planetary nebula we may turn with the five-inch to No. 4234. It is very small and faint, only 8" in diameter, and equal inbrightness to an eighth-magnitude star. Only close gazing shows that itis not sharply defined like a star, and that it possesses a bluish tint. Its spectrum is gaseous. 

The chief attraction of Hercules we have left for the last, the famousstar cluster between eta and zeta, No. 4230, more commonly known as M13. On a still evening in the early summer, when the moon is absent andthe quiet that the earth enjoys seems an influence descending from thebrooding stars, the spectacle of this sun cluster in Hercules, viewedwith a telescope of not less than five-inches aperture, captivates themind of the most uncontemplative observer. With the Lick telescope Ihave watched it resolve into separate stars to its very center--a sceneof marvelous beauty and impressiveness. But smaller instruments revealonly the in-running star streams and the sprinkling of stellar pointsover the main aggregation, which cause it to sparkle like a cloud ofdiamond dust transfused with sunbeams. The appearance of flockingtogether that those uncountable thousands of stars present calls up atonce a picture of our lone sun separated from its nearest stellarneighbor by a distance probably a hundred times as great as the entirediameter of the spherical space within which that multitude iscongregated. It is true that unless we assume what would seem anunreasonable remoteness for the Hercules cluster, its component starsmust be much smaller bodies than the sun; yet even that fact does notdiminish the wonder of their swarming. Here the imagination must bearscience on its wings, else science can make no progress whatever. It isan easy step from Hercules to Draco. In the conspicuous diamond-shapedfigure that serves as a guide-board to the head of the latter, thesouthernmost star belongs not to Draco but to Hercules. The brighteststar in this figure is gamma, of magnitude two and a half, with aneleventh-magnitude companion, distant 125", p. 116°. Two stars ofmagnitude five compose nu, their distance apart being 62", p. 312°. Amore interesting double is, magnitudes five and five, distance 2. 4", p. 158°. Both stars are white, and they present a pretty appearance whenthe air is steady. They form a binary system of unknown period. Sigma2078 (also called 17 Draconis) is a triple, magnitudes six, six and ahalf, and six, distances 3. 8", p. 116°, and 90", p. 195°. Sigma 1984 isan easy double, magnitudes six and a half and eight and a half, distance6. 4", p. 276°. The star eta is a very difficult double for even ourlargest aperture, on account of the faintness of one of its components. The magnitudes are two and a half and ten, distance 4. 7", p. 140°. Itsnear neighbor, Sigma 2054, may be a binary. Its magnitudes are six andseven, distance 1", p. 0°. In Sigma 2323 we have another triple, magnitudes five, eight and a half, and seven, distances 3. 6", p. 360°, and 90", p. 22°, colors white, blue, and reddish. A fine double isepsilon, magnitudes five and eight, distance 3", p. 5°. 

The nebula No. 4373 is of a planetary character, and interesting asoccupying the pole of the ecliptic. A few years ago Dr. Holden, with theLick telescope, discovered that it is unique in its form. It consists ofa double spiral, drawn out nearly in the line of sight, like the threadof a screw whose axis lies approximately endwise with respect to theobserver. There is a central star, and another fainter star is involvedin the outer spiral. The form of this object suggests strange ideas asto its origin. But the details mentioned are far beyond the reach ofour instruments. We shall only see it as a hazy speck. No. 4415 isanother nebula worth glancing at. It is Tuttle's so-called variablenebula. 

[Illustration: MAP NO. 16. ]

There are three constellations represented on map No. 16 to which weshall pay brief visits. First Aquila demands attention. Its doubles maybe summarized as follows: 11, magnitudes five and nine, distance 17. 4", p. 252°; pi, magnitudes six and seven, distance 1. 6", p. 122°; 23, magnitudes six and ten, distance 3. 4", p. 12°--requires the five-inchand good seeing; 57, magnitudes five and six, distance 36", p. 170°;Sigma 2654, magnitudes six and eight, distance 12", p. 234°; Sigma 2644, magnitudes six and seven, distance 3. 6", p. 208°. 

The star eta is an interesting variable between magnitudes three and ahalf and 4. 7; period, seven days, four hours, fourteen minutes. Thesmall red variable R changes from magnitude six to magnitude seven and ahalf and back again in a period of three hundred and fifty-one days. 

Star cluster No. 4440 is a striking object, its stars ranging from theninth down to the twelfth magnitude. 

Just north of Aquila is the little constellation Sagitta, containingseveral interesting doubles and many fine star fields, which may bediscovered by sweeping over it with a low-power eyepiece. The star zetais double, magnitudes five and nine, distance 8. 6", p. 312°. The largerstar is itself double, but far too close to be split, except with verylarge telescopes. In theta we find three components of magnitudes seven, nine, and eight respectively, distances 11. 4", p. 327°, and 70", p. 227°. A wide double is epsilon, magnitudes six and eight, distance 92", p. 81°. Nebula No. 4572 is planetary. 

Turning to Delphinus, we find a very beautiful double in gamma, magnitudes four and five, distance 11", p. 273°, colors golden andemerald. The leader alpha, which is not as bright as its neighbor beta, and which is believed to be irregularly variable, is of magnitude four, and has a companion of nine and a half magnitude at the distance 35", p. 278°. At a similar distance, 35", p. 335°, beta has aneleventh-magnitude companion, and the main star is also double, butexcessively close, and much beyond our reach. It is believed to be aswiftly moving binary, whose stars are never separated widely enough tobe distinguished with common telescopes. 

CHAPTER VI

FROM LYRA TO ERIDANUS

"This Orpheus struck when with his wondrous songHe charmed the woods and drew the rocks along. "--MANILIUS. 

[Illustration: MAP NO. 17. ]

We resume our celestial explorations with the little constellation Lyra, whose chief star, Vega (alpha), has a very good claim to be regarded asthe most beautiful in the sky. The position of this remarkable star isindicated in map No. 17. Every eye not insensitive to delicate shades ofcolor perceives at once that Vega is not white, but blue-white. When thetelescope is turned upon the star the color brightens splendidly. Indeed, some glasses decidedly exaggerate the blueness of Vega, but theeffect is so beautiful that one can easily forgive the opticalimperfection which produces it. With our four-inch we look for thewell-known companion of Vega, a tenth-magnitude star, also of a bluecolor deeper than the hue of its great neighbor. The distance is 50", p. 158°. Under the most favorable circumstances it might be glimpsed withthe three-inch, but, upon the whole, I should regard it as too severe atest for so small an aperture. 

Vega is one of those stars which evidently are not only enormouslylarger than the sun (one estimate makes the ratio in this case ninehundred to one), but whose physical condition, as far as thespectroscope reveals it, is very different from that of our ruling orb. Like Sirius, Vega displays the lines of hydrogen most conspicuously, andit is probably a much hotter as well as a much more voluminous bodythan the sun. 

Close by, toward the east, two fourth-magnitude stars form a littletriangle with Vega. Both are interesting objects for the telescope, andthe northern one, epsilon, has few rivals in this respect. Let us firstlook at it with an opera glass. The slight magnifying power of such aninstrument divides the star into two twinkling points. They are abouttwo and a quarter minutes of arc apart, and exceptionally sharp-sightedpersons are able to see them divided with the naked eye. Now take thethree-inch telescope and look at them, with a moderate power. Each ofthe two stars revealed by the opera glass appears double, and a fifthstar of the ninth magnitude is seen on one side of an imaginary linejoining the two pairs. The northern-most pair is named epsilon_1, themagnitudes being fifth and sixth, distance 3", p. 15°. The other pair isepsilon_2, magnitudes fifth and sixth, distance 2. 3", p. 133°. Each pairis apparently a binary; but the period of revolution is unknown. Somehave guessed a thousand years for one pair, and two thousand for theother. Another guess gives epsilon_1 a period of one thousand years, andepsilon_2 a period of eight hundred years. Hall, in his double-starobservations, simply says of each, "A slow motion. "

Purely by guesswork a period has also been assigned to the two pairs ina supposed revolution around their common center, the time named beingabout a million years. It is not known, however, that such a motionexists. Manifestly it could not be ascertained within the brief periodduring which scientific observations of these stars have been made. Theimportance of the element of time in the study of stellar motions isfrequently overlooked, though not, of course, by those who are engagedin such work. The sun, for instance, and many of the stars are knownto be moving in what appear to be straight lines in space, butobservations extending over thousands of years would probably show thatthese motions are in curved paths, and perhaps in closed orbits. 

If now in turn we take our four-inch glass, we shall see something elsein this strange family group of epsilon Lyræ. Between epsilon_1 andepsilon_2, and placed one on each side of the joining line, appear twoexceedingly faint specks of light, which Sir John Herschel made famousunder the name of the _debillissima_. They are of the twelfth orthirteenth magnitude, and possibly variable to a slight degree. If youcan not see them at first, turn your eye toward one side of the field ofview, and thus, by bringing their images upon a more sensitive part ofthe retina, you may glimpse them. The sight is not much, yet it willrepay you, as every glance into the depths of the universe does. 

The other fourth-magnitude star near Vega is zeta, a wide double, magnitudes fourth and sixth, distance 44", p. 150°. Below we find beta, another very interesting star, since it is both a multiple and aneccentric variable. It has four companions, three of which we can easilysee with our three-inch; the fourth calls for the five-inch; themagnitudes are respectively four, seven or under, eight, eight and ahalf, and eleven; distances 45", p. 150°; 65", p. 320°; 85", p. 20°; and46", p. 248°. The primary, beta, varies from about magnitude three and ahalf to magnitude four and a half, the period being twelve days, twenty-one hours, forty-six minutes, and fifty-eight seconds. Twounequal maxima and minima occur within this period. In the spectrum ofthis star some of the hydrogen lines and the D_3 line (the latterrepresenting helium, a constituent of the sun and of some of the stars, which, until its recent discovery in a few rare minerals was not knownto exist on the earth) are bright, but they vary in visibility. Moreover, dark lines due to hydrogen also appear in its spectrumsimultaneously with the bright lines of that element. Then, too, thebright lines are sometimes seen double. Professor Pickering'sexplanation is that beta Lyræ probably consists of two stars, which, like the two composing beta Aurigæ, are too close to be separated withany telescope now existing, and that the body which gives the brightlines is revolving in a circle in a period of about twelve days andtwenty-two hours around the body which gives the dark lines. He has alsosuggested that the appearances could be accounted for by supposing abody like our sun to be rotating in twelve days and twenty-two hours, and having attached to it an enormous protuberance extending over morethan one hundred and eighty degrees of longitude, so that when one endof it was approaching us with the rotation of the star the other endwould be receding, and a splitting of the spectral lines at certainperiods would be the consequence. "The variation in light, " he adds, "may be caused by the visibility of a larger or smaller portion of thisprotuberance. "

Unfortunate star, doomed to carry its parasitical burden of hydrogen andhelium, like Sindbad in the clasp of the Old Man of the Sea! Surely, thehuman imagination is never so wonderful as when it bears an astronomeron its wings. Yet it must be admitted that the facts in this case arewell calculated to summon the genius of hypothesis. And the puzzle ishardly simplified by Bélopolsky's observation that the body in beta Lyrægiving dark hydrogen lines shows those lines also split at certaintimes. It has been calculated, from a study of the phenomena notedabove, that the bright-line star in beta Lyræ is situated at a distanceof about fifteen million miles from the center of gravity of thecuriously complicated system of which it forms a part. 

We have not yet exhausted the wonders of Lyra. On a line from beta togamma, and about one third of the distance from the former to thelatter, is the celebrated Ring Nebula, indicated on the map by thenumber 4447. We need all the light we can get to see this object well, and so, although the three-inch will show it, we shall use thefive-inch. Beginning with a power of one hundred diameters, whichexhibits it as a minute elliptical ring, rather misty, very soft anddelicate, and yet distinct, we increase the magnification first to twohundred and finally to three hundred, in order to distinguish a littlebetter some of the details of its shape. Upon the whole, however, wefind that the lowest power that clearly brings out the ring gives themost satisfactory view. The circumference of the ring is greater thanthat of the planet Jupiter. Its ellipticity is conspicuous, the lengthof the longer axis being 78" and that of the shorter 60". Closelyfollowing the nebula as it moves through the field of view, ourfive-inch telescope reveals a faint star of the eleventh or twelfthmagnitude, which is suspected of variability. The largest instruments, like the Washington and the Lick glasses, have shown perhaps a dozenother stars apparently connected with the nebula. A beautiful sparklingeffect which the nebula presents was once thought to be an indicationthat it was really composed of a circle of stars, but the spectroscopeshows that its constitution is gaseous. Just in the middle of the openring is a feeble star, a mere spark in the most powerful telescope. Butwhen the Ring Nebula is photographed--and this is seen beautifully inthe photographs made with the Crossley reflector on Mount Hamilton bythe late Prof. J. E. Keeler--this excessively faint star imprints itsimage boldly as a large bright blur, encircled by the nebulous ring, which itself appears to consist of a series of intertwisted spirals. 

Not far away we find a difficult double star, 17, whose components areof magnitudes six and ten or eleven, distance 3. 7", p. 325°. 

From Lyra we pass to Cygnus, which, lying in one of the richest parts ofthe Milky Way, is a very interesting constellation for the possessor ofa telescope. Its general outlines are plainly marked for the naked eyeby the figure of a cross more than twenty degrees in length lying alongthe axis of the Milky Way. The foot of the cross is indicated by thestar beta, also known as Albireo, one of the most charming of all thedouble stars. The three-inch amply suffices to reveal the beauty of thisobject, whose components present as sharp a contrast of light yellow anddeep blue as it would be possible to produce artificially with thepurest pigments. The magnitudes are three and seven, distance 34. 6", p. 55°. No motion has been detected indicating that these stars areconnected in orbital revolution, yet no one can look at them withoutfeeling that they are intimately related to one another. It is a sightto which one returns again and again, always with undiminished pleasure. The most inexperienced observer admires its beauty, and after an hourspent with doubtful results in trying to interest a tyro in double starsit is always with a sense of assured success that one turns thetelescope to beta Cygni. 

Following up the beam of the imaginary cross along the current of theMilky Way, every square degree of which is here worth long gazing into, we come to a pair of stars which contend for the name-letter chi. On ourmap the letter is attached to the southernmost of the two, a variable oflong period--four hundred and six days--whose changes of brilliance liebetween magnitudes four and thirteen, but which exhibits muchirregularity in its maxima. The other star, not named but easilyrecognized in the map, is sometimes called 17. It is an attractivedouble whose colors faintly reproduce those of beta. The magnitudes arefive and eight, distance 26", p. 73°. Where the two arms of the crossmeet is gamma, whose remarkable _cortége_ of small stars running incurved streams should not be missed. Use the lowest magnifying power. 

At the extremity of the western arm of the cross is delta, a closedouble, difficult for telescopes of moderate aperture on account of thedifference in the magnitudes of the components. We may succeed individing it with the five-inch. The magnitudes are three and eight, distance 1. 5", p. 310°. It is regarded as a binary of long and as yetunascertained period. 

In omicron^2 we find a star of magnitude four and orange in color, having two blue companions, the first of magnitude seven and a half, distance 107", p. 174°, and the second of magnitude five and a half, distance 358", p. 324°. Farther north is psi, which presents to us thecombination of a white five-and-a-half-magnitude star with a lilac starof magnitude seven and a half. The distance is 3", p. 184°. A verypretty sight. 

We now pass to the extremity of the other arm of the cross, near whichlies the beautiful little double 49, whose components are of magnitudessix and eight, distance 2. 8", p. 50°. The colors are yellow and blue, conspicuous and finely contrasted. A neighboring double of similar huesis 52, in which the magnitudes are four and nine, distance 6", p. 60°. Sweeping a little way northward we come upon an interesting binary, lambda, which is unfortunately beyond the dividing power of our largestglass. A good seven-inch or seven-and-a-half-inch should split it underfavorable circumstances. Its magnitudes are six and seven, distance0. 66", p. 74°. 

The next step carries us to a very famous object, 61 Cygni, long knownas the nearest star in the northern hemisphere of the heavens. It is adouble which our three-inch will readily divide, the magnitudes beingboth six, distance 21", p. 122°. The distance of 61 Cygni, according toHall's parallax of 0. 27", is about 70, 000, 000, 000, 000 miles. There issome question whether or not it is a binary, for, while the twin starsare both moving in the same direction in space with comparativerapidity, yet conclusive evidence of orbital motion is lacking. When onehas noticed the contrast in apparent size between this comparativelynear-by star, which the naked eye only detects with considerabledifficulty, and some of its brilliant neighbors whose distance is sogreat as to be immeasurable with our present means, no better proof willbe needed of the fact that the faintness of a star is not necessarily anindication of remoteness. 

We may prepare our eyes for a beautiful exhibition of contrasted colorsonce more in the star . This is really a quadruple, although only two ofits components are close and conspicuous. The magnitudes are five, six, seven and a half, and twelve; distances 2. 4", p. 121°; 208", p. 56°; and35", p. 264°. The color of the largest star is white and that of itsnearest companion blue; the star of magnitude seven and a half is alsoblue. 

The star cluster 4681 is a fine sight with our largest glass. In the mapwe find the place marked where the new star of 1876 made its appearance. This was first noticed on November 24, 1876, when it shone with thebrilliance of a star of magnitude three and a half. Its spectrum wascarefully studied, especially by Vogel, and the very interesting changesthat it underwent were noted. Within a year the star had faded to lessthan the tenth magnitude, and its spectrum had completely changed inappearance, and had come to bear a close resemblance to that of aplanetary nebula. This has been quoted as a possible instance of acelestial collision through whose effects the solid colliding masseswere vaporized and expanded into a nebula. At present the star is veryfaint and can only be seen with the most powerful telescopes. Comparewith the case of Nova Aurigæ, previously discussed. 

Underneath Cygnus we notice the small constellation Vulpecula. Itcontains a few objects worthy of attention, the first being the nebula4532, the "dumb-bell nebula" of Lord Rosse. With the four-inch, andbetter with the five-inch, we are able to perceive that it consists oftwo close-lying tufts of misty light. Many stars surround it, and largetelescopes show them scattered between the two main masses of thenebula. The Lick photographs show that its structure is spiral. The star11 points out the place where a new star of the third magnitude appearedin 1670. Sigma 2695 is a close double, magnitudes six and eight, distance 0. 96", p. 78°. 

[Illustration: MAP NO. 18. ]

We turn to map No. 18, and, beginning at the western end of theconstellation Aquarius, we find the variable T, which ranges betweenmagnitudes seven and thirteen in a period of about two hundred and threedays. Its near neighbor Sigma 2729 is a very close double, beyond theseparating power of our five-inch, the magnitudes being six and seven, distance 0. 6", p. 176°. Sigma 2745, also known as 12 Aquarii, is a gooddouble for the three-inch. Its magnitudes are six and eight, distance2. 8", p. 190°. In zeta we discover a beauty. It is a slow binary ofmagnitudes four and four, distance 3. 1", p. 321°. According to someobservers both stars have a greenish tinge. The star 41 is a widerdouble, magnitudes six and eight, distance 5", p. 115°, colors yellowand blue. The uncommon stellar contrast of white with light garnet isexhibited by tau, magnitudes six and nine, distance 27", p. 115°. Yellowand blue occur again conspicuously in psi, magnitudes four and a halfand eight and a half, distance 50", p. 310°. Rose and emerald have beenrecorded as the colors exhibited in Sigma 2998, whose magnitudes arefive and seven, distance 1. 3", p. 346°. 

The variables S and R are both red. The former ranges between magnitudeseight and twelve, period two hundred and eighty days, and the latterbetween magnitudes six and eleven, period about three hundred and ninetydays. 

The nebula 4628 is Rosse's "Saturn nebula, " so called because with hisgreat telescope it presented the appearance of a nebulous model of theplanet Saturn. With our five-inch we see it simply as a planetarynebula. We may also glance at another nebula, 4678, which appearscircular and is pinned with a little star at the edge. 

The small constellation Equuleus contains a surprisingly large number ofinteresting objects. Sigma 2735 is a rather close double, magnitudes sixand eight, distance 1. 8", p. 287°. Sigma 2737 (the first star to theleft of Sigma 2735, the name having accidentally been omitted from themap) is a beautiful triple, although the two closest stars, ofmagnitudes six and seven, can not be separated by our instruments. Theirdistance in 1886 was 0. 78", p. 286°, and they had then been closingrapidly since 1884, when the distance was 1. 26". The third star, ofmagnitude eight, is distant 11", p. 75°. Sigma 2744 consists of twostars, magnitudes six and seven, distance 1. 4", p. 1. 67°. It is probablya binary. Sigma 2742 is wider double, magnitudes both six, distance2. 6", p. 225°. Another triple, one of whose components is beyond ourreach, is gamma. Here the magnitudes are fifth, twelfth, and sixth, distances 2", p. 274° and 366". It would also be useless for us to tryto separate delta, but it is interesting to remember that this is one ofthe closest of known double stars, the magnitudes being fourth andfifth, distance 0. 4", p. 198°. These data are from Hall's measurementsin 1887. The star is, no doubt, a binary. With the five-inch we maydetect one and perhaps two of the companion stars in the quadruple beta. The magnitudes are five, ten, and two eleven, distances 67", p. 309°;86", p. 276°; and 6. 5", p. 15°. The close pair is comprised in thetenth-magnitude star. 

[Illustration: MAP NO. 19. ]

Map No. 19 introduces us to the constellation Pegasus, which iscomparatively barren to the naked eye, and by no means rich intelescopic phenomena. The star epsilon, of magnitude two and a half, hasa blue companion of the eighth magnitude, distance 138", p. 324°; colorsyellow and violet. A curious experiment that may be tried with this staris described by Webb, who ascribes the discovery of the phenomenon toSir John Herschel. When near the meridian the small star in epsilonappears, in the telescope, underneath the large one. If now the tube ofthe telescope be slightly swung from side to side the small star willappear to describe a pendulumlike movement with respect to the largeone. The explanation suggested is that the comparative faintness of thesmall star causes its light to affect the retina of the eye less quicklythan does that of its brighter companion, and, in consequence, thereversal of its apparent motion with the swinging of the telescope isnot perceived so soon. 

The third-magnitude star eta has a companion of magnitude ten and ahalf, distance 90", p. 340°. The star beta, of the second magnitude, andreddish, is variable to the extent of half a magnitude in an irregularperiod, and gamma, of magnitude two and a half, has aneleventh-magnitude companion, distance 162", p. 285°. 

[Illustration: MAP NO. 20. ]

Our interest is revived on turning, with the guidance of map No. 20, from the comparative poverty of Pegasus to the spacious constellationCetus. The first double star that we meet in this constellation is 26, whose components are of magnitudes six and nine, distance 16. 4", p. 252°; colors, topaz and lilac. Not far away is the closer double 42, composed of a sixth and a seventh magnitude star, distance 1. 25", p. 350°. The four-inch is capable of splitting this star, but we shall dobetter to use the five-inch. In passing we may glance at thetenth-magnitude companion to eta, distance 225", p. 304°. Another widepair is found in zeta, magnitudes three and nine, distance 185", p. 40°. 

The next step brings us to the wonderful variable omicron, or Mira, whose changes have been watched for three centuries, the first observerof the variability of the star having been David Fabricius in 1596. Notonly is the range of variability very great, but the period isremarkably irregular. In the time of Hevelius, Mira was once invisiblefor four years. When brightest, the star is of about the secondmagnitude, and when faintest, of the ninth magnitude, but at maximum itseldom exhibits the greatest brilliance that it has on a few occasionsshown itself capable of attaining. Ordinarily it begins to fade afterreaching the fourth or fifth magnitude. The period averages about threehundred and thirty-one days, but is irregularly variable to the extentof twenty-five days. Its color is red, and its spectrum shows brightlines, which it is believed disappear when the star sinks to a minimum. Among the various theories proposed to account for such changes as thesethe most probable appears to be that which ascribes them to some causeanalogous to that operating in the production of sun spots. Theoutburst of light, however, as pointed out by Scheiner, should beregarded as corresponding to the maximum and not the minimum stage ofsun-spot activity. According to this view, the star is to be regarded aspossessing an extensive atmosphere of hydrogen, which, during themaximum, is upheaved into enormous prominences, and the brilliance ofthe light from these prominences suffices to swamp the photosphericlight, so that in the spectrum the hydrogen lines appear bright insteadof dark. 

It is not possible to suppose that Mira can be the center of a system ofhabitable planets, no matter what we may think of the more constantstars in that regard, because its radiation manifestly increases morethan six hundred fold, and then falls off again to an equal extent oncein every ten or eleven months. I have met people who can not believethat the Almighty would make a sun and then allow its energies "to go towaste, " by not supplying it with a family of worlds. But I imagine thatif they had to live within the precincts of Mira Ceti they would cry outfor exemption from their own law of stellar utility. 

The most beautiful double star in Cetus is gamma, magnitudes three andseven, distance 3", p. 288°; hues, straw-color and blue. The leadingstar alpha, of magnitude two and a half, has a distant blue companionthree magnitudes fainter, and between them are two minute stars, thesouthernmost of which is a double, magnitudes both eleven, distance 10", p. 225°. 

The variable S ranges between magnitudes seven and twelve in a somewhatirregular period of about eleven months, while R ranges between theseventh and the thirteenth magnitudes in a period of one hundred andsixty-seven days. 

[Illustration: MAP NO. 21. ]

The constellation Eridanus, represented in map No. 21, contains a fewfine double stars, one of the most interesting of which is 12, a ratherclose binary. The magnitudes are four and eight, distance 2", p. 327°. We shall take the five-inch for this, and a steady atmosphere and sharpseeing will be necessary on account of the wide difference in thebrightness of the component stars. Amateurs frequently fail to make dueallowance for the effect of such difference. When the limit ofseparating power for a telescope of a particular aperture is set at 1"or 2", as the case may be, it is assumed that the stars composing thedoubles on which the test is made shall be of nearly the same magnitude, or at least that they shall not differ by more than one or twomagnitudes at the most. The stray light surrounding a comparativelybright star tends to conceal a faint companion, although the telescopemay perfectly separate them so far as the stellar disks are concerned. Then, too, I have observed in my own experience that a very faint andclose double is more difficult than a brighter pair not more widelyseparated, usually on account of the defect of light, and this is trueeven when the components of the faint double are of equal magnitude. 

Sigma 470, otherwise known as 32 Eridani, is a superb object on accountof the colors of its components, the larger star being a rich topaz andthe smaller an ultramarine; while the difference in magnitude is not asgreat as in many of the colored doubles. The magnitudes are five andseven, distance 6. 7", p. 348°. The star gamma, of magnitude two and ahalf, has a tenth-magnitude companion, distant 51", p. 238°. Sigma 516, also called 39 Eridani, consists of two stars of magnitudes six andnine, distance 6. 4", p. 150°; colors, yellow and blue. The supposedbinary character of this star has not yet been established. 

In omicron^2 we come upon an interesting triple star, two of whosecomponents at any rate we can easily see. The largest component is ofthe fourth magnitude. At a distance of 82", p. 105°, we find atenth-magnitude companion. This companion is itself double, themagnitudes of its components being ten and eleven, distance 2. 6", p. 98°. Hall says of these stars that they "form a remarkable system. " Hehas also observed a fourth star of the twelfth magnitude, distant 45"from the largest star, p. 85°. This is apparently unconnected with theothers, although it is only half as distant as the tenth-magnitudecomponent is from the primary. Sigma 590 is interesting because of thesimilarity of its two components in size, both being of about theseventh magnitude, distance 10", p. 318°. 

Finally, we turn to the nebula 826. This is planetary in form andinconspicuous, but Lassell has described it as presenting a mostextraordinary appearance with his great reflector--a circular nebulalying upon another fainter and larger nebula of a similar shape, andhaving a star in its center. Yet it may possibly be an immensely distantstar cluster instead of a nebula, since its spectrum does not appear tobe gaseous. 

CHAPTER VII

PISCES, ARIES, TAURUS, AND THE NORTHERN STARS

"Now sing we stormy skies when Autumn weighsThe year, and adds to nights and shortens days, And suns declining shine with feeble rays. "--DRYDEN'S VIRGIL. 

[Illustration: MAP NO. 22. ]

The eastern end of Pisces, represented in map No. 22, includes most ofthe interesting telescopic objects that the constellation contains. Webegin our exploration at the star numbered 55, a double that is verybeautiful when viewed with the three-inch glass. The components are ofmagnitudes five and eight, distance 6. 6", p. 192°. The larger star isyellow and the smaller deep blue. The star 65, while lacking thepeculiar charm of contrasted colors so finely displayed in 55, possessesan attraction in the equality of its components which are both of thesixth magnitude and milk-white. The distance is 4. 5", p. 118°. In 66 wefind a swift binary whose components are at present far too close forany except the largest telescopes. The distance in 1894 was only 0. 36", p. 329°. The magnitudes are six and seven. In contrast with thisexcessively close double is psi, whose components are both of magnitudefive and a half, distance 30", p. 160°. Dropping down to 77 we come uponanother very wide and pleasing double, magnitudes six and seven, distance 33", p. 82°, colors white and lilac or pale blue. Hardly lessbeautiful is zeta magnitudes five and six, distance 24", p. 64°. Finestof all is alpha, which exhibits a remarkable color contrast, the largerstar being greenish and the smaller blue. The magnitudes are four andfive, distance 3", p. 320°. This star is a binary, but the motion isslow. The variable R ranges between magnitudes seven and thirteen, period three hundred and forty-four days. 

The constellation Aries contains several beautiful doubles, all but oneof which are easy for our smallest aperture. The most striking of theseis gamma, which is historically interesting as the first double stardiscovered. The discovery was made by Robert Hooke in 1664 by accident, while he was following the comet of that year with his telescope. Heexpressed great surprise on noticing that the glass divided the star, and remarked that he had not met with a like instance in all theheavens. His observations could not have been very extensive or verycarefully conducted, for there are many double stars much wider thangamma Arietis which Hooke could certainly have separated if he hadexamined them. The magnitudes of the components of gamma are four andfour and a half, or, according to Hall, both four; distance 8. 5", p. 180°. A few degrees above gamma, passing by beta, is a wide doublelambda, magnitudes five and eight, distance 37", p. 45°, colors whiteand lilac or violet. Three stars are to be seen in 14: magnitudes fiveand a half, ten, and nine, distances 83", p. 36°, and 106", p. 278°, colors white, blue, and lilac. The star 30 is a very pretty double, magnitudes six and seven, distance 38. 6", p. 273°. Sigma 289 consists ofa topaz star combined with a sapphire, magnitudes six and nine, distance28. 5", p. 0°. The fourth-magnitude star 41 has several faint companions. The magnitudes of two of these are eleven and nine, distances 34", p. 203°, and 130", p. 230°. We discover another triple in pi, magnitudesfive, eight, and eleven, distances 3. 24", p. 122°, and 25", p. 110°. Thedouble mentioned above as being too close for our three-inch glass isepsilon, which, however, can be divided with the four-inch, although thefive-inch will serve us better. The magnitudes are five and a half andsix, distance 1. 26", p. 202°. The star 52 has two companions, one ofwhich is so close that our instruments can not separate it, while theother is too faint to be visible in the light of its brilliant neighborwithout the aid of a very powerful telescope. 

[Illustration: MAP NO. 23. ]

We are now about to enter one of the most magnificent regions in thesky, which is hardly less attractive to the naked eye than Orion, andwhich men must have admired from the beginning of their history on theearth, the constellation Taurus (map No. 23). Two groups of starsespecially distinguish Taurus, the Hyades and the Pleiades, and both areexceedingly interesting when viewed with the lowest magnifying powers ofour telescopes. 

We shall begin with a little star just west of the Pleiades, Sigma 412, also called 7 Tauri. This is a triple, but we can see it only as adouble, the third star being exceedingly close to the primary. Themagnitudes are six and a half, seven, and ten, distances 0. 3", p. 216°, and 22", p. 62°. In the Pleiades we naturally turn to the brightest stareta, or Alcyone, famous for having once been regarded as the central sunaround which our sun and a multitude of other luminaries were supposedto revolve, and picturesque on account of the little triangle of smallstars near it which the least telescopic assistance enables us to see. One may derive much pleasure from a study of the various groupings ofstars in the Pleiades. Photography has demonstrated, what had long beensuspected from occasional glimpses revealed by the telescope, that thiscelebrated cluster of stars is intermingled with curious forms ofnebulæ. The nebulous matter appears in festoons, apparently attached tosome of the larger stars, such as Alcyone, Merope, and Maia, and inlong, narrow, straight lines, the most remarkable of which, a faintlyluminous thread starting midway between Maia and Alcyone and runningeastward some 40', is beaded with seven or eight stars. The width ofthis strange nebulous streak is, on an average, 3" or 4", and there is, perhaps, no more wonderful phenomenon anywhere in celestial space. Unfortunately, no telescope is able to show it, and all our knowledgeabout it is based upon photographs. It might be supposed that it was anebulous disk seen edgewise, but for the fact that at the largest starinvolved in its course it bends sharply about 10° out of its formerdirection, and for the additional fact that it seems to take its originfrom a curved offshoot of the intricate nebulous mass surrounding Maia. Exactly at the point where this curve is transformed into a straightline shines a small star! In view of all the facts the idea does notseem to be very far-fetched that in the Pleiades we behold an assemblageof suns, large and small, formed by the gradual condensation of anebula, and in which evolution has gone on far beyond the stagerepresented by the Orion nebula, where also a group of stars may be inprocess of formation out of nebulous matter. If we look a little fartheralong this line of development, we may perceive in such a stellarassemblage as the cluster in Hercules, a still later phase wherein allthe originally scattered material has, perhaps, been absorbed into thestarry nuclei. 

[Illustration: THE CHIEF STARS IN THE PLEIADES. ]

The yellow star Sigma 430 has two companions: magnitudes six, nine, andnine and a half, distances 26", p. 55°, and 39", p. 302°. The star 30 ofthe fifth magnitude has a companion of the ninth magnitude, distance 9", p. 58°, colors emerald and purple, faint. An interesting variable, ofthe type of Algol, is lambda, which at maximum is of magnitude three andfour tenths and at minimum of magnitude four and two tenths. Its periodfrom one maximum to the next is about three days and twenty-three hours, but the actual changes occupy only about ten hours, and it loses lightmore swiftly than it regains it. A combination of red and blue ispresented by Phi (mistakenly marked on map No. 23 as psi). Themagnitudes are six and eight, distance 56", p. 242°. A double of similarmagnitudes is chi, distance 19", p. 25°. Between the two stars which thenaked eye sees in kappa is a minute pair, each of less than the eleventhmagnitude, distance 5", p. 324°. Another naked-eye double is formed bytheta^1 and theta^2, in the Hyades. The magnitudes are five and five anda half, distance about 5' 37". 

The leading star of Taurus, Aldebaran (alpha), is celebrated for itsreddish color. The precise hue is rather uncertain, but Aldebaran is notorange as Betelgeuse in Orion is, and no correct eye can for an instantconfuse the colors of these two stars, although many persons seem to beunable to detect the very plain difference between them in this respect. Aldebaran has been called "rose-red, " and it would be an interestingoccupation for an amateur to determine, with the aid of some propercolor scale, the precise hue of this star, and of the many other starswhich exhibit chromatic idiosyncrasy. Aldebaran is further interestingas being a standard first-magnitude star. With the four-inch glass wesee without difficulty the tenth-magnitude companion following Aldebaranat a distance of 114", p. 35°. There is an almost inexplicable charmabout these faint attendants of bright stars, which is quite differentfrom the interest attaching to a close and nearly equal pair. Theimpression of physical relationship is never lacking though it may bedeceptive, and this awakens a lively appreciation of the vastdifferences of magnitude that exist among the different suns of space. 

The actual size and might of this great red sun form an attractivesubject for contemplation. As it appears to our eyes Aldebaran gives onetwenty-five-thousand-millionth as much light as the sun, but if we wereplaced midway between them the star would outshine the sun in the ratioof not less than 160 to 1. And yet, gigantic as it is, Aldebaran ispossibly a pygmy in comparison with Arcturus, whose possible dimensionswere discussed in the chapter relating to Boötes. Although Aldebaran isknown to possess several of the metallic elements that exist in the sun, its spectrum differs widely from the solar spectrum in some respects, and more closely resembles that of Arcturus. 

Other interesting objects in Taurus are sigma, divisible with the nakedeye, magnitudes five and five and a half, distance 7'; Sigma 674, double, magnitudes six and nine, distance 10. 5", p. 147°; Sigma 716, double, magnitudes six and seven, distance 5", p. 200°--a pleasingsight; tau, triple, magnitudes four, ten and a half, and eleven, distances 36", p. 249°, and 36", p. 60°--the ten-and-a-half-magnitudestar is itself double, as discovered by Burnham; star cluster No. 1030, not quite as broad as the moon, and containing some stars as large asthe eleventh magnitude; and nebula No. 1157, the so-called "Crab nebula"of Lord Rosse, which our glasses will show only as a misty patch offaint light, although large telescopes reveal in it a very curiousstructure. 

[Illustration: MAP NO. 24. ]

We now turn to the cluster of circumpolar constellations sometimescalled the Royal Family, in allusion to the well-known story of theEthiopian king Cepheus and his queen Cassiopeia, whose daughterAndromeda was exposed on the seashore to be devoured by a monster, butwho was saved by the hero Perseus. All these mythologic personages arerepresented in the constellations that we are about to study. [4] Webegin with Andromeda (map No. 24). The leading star alpha marks onecorner of the great square of Pegasus. The first star of telescopicinterest that we find in Andromeda is, a double difficult on account ofthe faintness of the smaller component. The magnitudes are four andeleven, distance 49", p. 110°. A few degrees north of the naked eyedetects a glimmering point where lies the Great Nebula in Andromeda. This is indicated on the map by the number 116. With either of our threetelescopes it is an interesting object, but of course it is advisable touse our largest glass in order to get as much light as possible. Allthat we can see is a long, shuttle-shaped nebulous object, having abrighter point near the center. Many stars are scattered over the fieldin its neighborhood, but the nebula itself, although its spectrum ispeculiar in resembling that of a faint star, is evidently a gaseous orat any rate a meteoritic mass, since photographs show it to be composedof a series of imperfectly separated spirals surrounding a vast centralcondensation. This peculiarity of the Andromeda nebula, which isinvisible with telescopes although conspicuous in the photographs, has, since its discovery a few years ago, given a great impetus tospeculation concerning the transformation of nebulæ into stars and starclusters. No one can look at a good photograph of this wonderfulphenomenon without noticing its resemblance to the ideal state of thingswhich, according to the nebular hypothesis, must once have existed inthe solar system. It is to be remembered, however, that there isprobably sufficient material in the Andromeda nebula to make a systemmany times, perhaps hundreds or thousands of times, as extensive as thatof which our sun is the center. If one contemplates this nebula onlylong enough to get a clear perception of the fact that creation was notended when, according to the Mosaic history, God, having in six daysfinished "the heavens and the earth and all the host of them, " restedfrom all his work, a good blow will have been dealt for the cause oftruth. Systems far vaster than ours are now in the bud, and long beforethey have bloomed, ambitious man, who once dreamed that all these thingswere created to serve him, will probably have vanished with theextinguishment of the little star whose radiant energy made his life andhis achievements briefly possible. 

[4] For further details on this subject see Astronomy with anOpera-glass. 

In August, 1885, a new star of magnitude six and a half made itsappearance suddenly near the center of the Andromeda nebula. Within oneyear it had disappeared, having gradually dwindled until the greatWashington telescope, then the largest in use, no longer showed it. Thatthis was a phenomenon connected with the nebula is most probable, butjust what occurred to produce it nobody knows. The observed appearancesmight have been produced by a collision, and no better hypothesis hasyet been suggested to account for them. 

Near the opposite end of the constellation from alpha we find the mostinteresting of triple stars in gamma. The two larger components of thisbeautiful star are of magnitudes three and six, distance 10", colorsgolden yellow and deep blue. The three-inch shows them finely. Thesmaller star is itself double, its companion being of magnitude eight, distance when discovered in 1842 0. 5", color bluish green. A few yearsago this third star got so close to its primary that it was invisibleeven with the highest powers of the great Lick telescope, but at presentit is widening again. In October, 1893, I had the pleasure of looking atgamma Andromedæ with the Lick telescope, and at that time it waspossible just to separate the third star. The angle seemed too small forcertain measurement, but a single setting of the micrometer by Mr. Barnard, to whose kindness I was indebted for my view of the star, gave0. 17" as the approximate distance. In 1900 the distance had increased to0. 4", p. 115°. The brilliance of color contrast between the two largerstars of gamma Andromedæ is hardly inferior to that exhibited in betaCygni, so that this star may be regarded as one of the most picturesqueof stellar objects for small telescopes. 

Other pleasing objects in this constellation are the binary star 36, magnitudes six and six and a half, distance 1", p. 17°--the two starsare slowly closing and the five-inch glass is required to separate them:the richly colored variable R, which fades from magnitude five and ahalf to invisibility, and then recovers its light in a period of aboutfour hundred and five days; and the bright star cluster 457, whichcovers a space about equal to the area of the full moon. 

Just south of the eastern end of Andromeda is the small constellationTriangulum, or the Triangles, containing two interesting objects. One ofthese is the beautiful little double 6, magnitudes five and six, distance 3. 8", p. 77°, colors yellow and blue; and the other, the nebula352, which equals in extent the star cluster in Andromeda describedabove, but nevertheless appears very faint with our largest glass. Itsfaintness, however, is not an indication of insignificance, for to verypowerful telescopes it exhibits a wonderful system of nuclei andspirals--another bit of chaos that is yielding by age-long steps to theinfluence of demiurgic forces. 

A richer constellation than Andromeda, both for naked-eye and telescopicobservation, is Perseus, which is especially remarkable for its starclusters. Two of these, 512 and 521, constitute the celebrated doublecluster, sometimes called the Sword-hand of Perseus, and also chiPersei. To the smallest telescope this aggregation of stars, ranging inmagnitude from six and a half to fourteen, and grouped about twoneighboring centers, presents a marvelous appearance. As an educativeobject for those unaccustomed to celestial observations it may becompared among star clusters to beta Cygni among double stars, for themost indifferent spectator is struck with wonder in viewing it. All theother clusters in Perseus represented on the map are worth examining, although none of them calls for special mention, except perhaps 584, where we may distinguish at least a hundred separate stars within anarea less than one quarter as expansive as the face of the moon. 

Among the double stars of Perseus we note first eta, whose componentsare of magnitudes four and eight, distance 28", colors white and paleblue. The double epsilon is especially interesting on account of analleged change of color from blue to red which the smaller starundergoes coincidently with a variation of brightness. The magnitudesare three and eight, distance 9", p. 9°. An interesting multiple iszeta, two of whose stars at least we can see. The magnitudes are three, nine, ten, and ten, distances 13", p. 207°, 90", and 112". 

The chief attraction in Perseus is the changeful and wonderful beta, orAlgol, the great typical star among the short-period variables. Duringthe greater part of its period this star is of magnitude two and twotenths, but for a very short time, following a rapid loss of light, itremains at magnitude three and seven tenths. The difference, onemagnitude and a half, corresponds to an actual difference in brightnessin the ratio of 3. 75 to 1. The entire loss of light during thedeclension occupies only four hours and a half. The star remains at itsfaintest for a few minutes only before a perceptible gain of lightoccurs, and the return to maximum is as rapid as was the precedingdecline. The period from one minimum to the next is two days twentyhours forty-eight minutes fifty-three seconds, with an irregularityamounting to a few seconds in a year. The Arabs named the star Algol, orthe Demon, on account of its eccentricity which did not escape theirattention; and when Goodricke, in 1782, applied a scientific method ofobservation to it, the real cause of its variations was suggested byhim, but his explanation failed of general acceptance until its truthwas established by Prof. E. C. Pickering in 1880. This explanation givesus a wonderful insight into stellar constitution. According to it, Algolpossesses a companion as large as the sun, but invisible, both becauseof its proximity to that star and because it yields no light, andrevolving in a plane horizontal to our line of sight. The period ofrevolution is identical with the period of Algol's cycle of variation, and the diminution of light is caused by the interposition of the darkbody as it sweeps along that part of its orbit lying between our pointof view and the disk of Algol. In other words, once in every two daystwenty hours and forty-nine minutes Algol, as seen from the earth, undergoes a partial eclipse. 

In consequence of the great comparative mass of its dark companion, Algol itself moves in an orbit around their common center with avelocity quite sufficient to be detected by the shifting of the lines inits spectrum. By means of data thus obtained the mass, size, anddistance apart of Algol and its singular comrade have been inferred. Thediameter of Algol is believed to be about 1, 125, 000 miles, that of thedark body about 840, 000 miles, and the mean distance from center tocenter 3, 230, 000 miles. The density of both the light and the dark staris slight compared with that of the sun, so that their combined mass isonly two thirds as great as the sun's. 

Mention has been made of a slight irregularity in Algol's period ofvariation. Basing his calculations upon this inequality, Dr. Chandlerhas put forward the hypothesis that there is another invisible bodyconnected with Algol, and situated at a distance from it of about1, 800, 000, 000 miles, and that around this body, which is far moremassive than the others, Algol and its companions revolve in a period ofone hundred and thirty years! Dr. Chandler has earned the right to havehis hypotheses regarded with respect, even when they are asextraordinary as that which has just been described. It needs noindulgence of the imagination to lend interest to Algol; the simplefacts are sufficient. How did that bright star fall in with its blackneighbors? Or were they created together?

[Illustration: MAP NO. 25. ]

Passing to the region covered by map No. 25, our eyes are caught by thecurious figure, formed by the five brightest stars of the constellationCassiopeia, somewhat resembling the letter W. Like Perseus, this is arich constellation, both in star clusters and double stars. Among thelatter we select as our first example sigma, in which we find acombination of color that is at once very unusual and verystriking--green and blue. The magnitudes are five and seven, distance3", p. 324°. Another beautiful colored double is eta, whose magnitudesare four and seven and a half, distance 5", p. 200°, colors white andpurple. This is one of the comparatively small number of stars themeasure of whose distance has been attempted, and a keen sense of theuncertainty of such measures is conveyed by the fact that authorities ofapparently equal weight place eta Cassiopeiæ at such discordantdistances as 124, 000, 000, 000, 000 miles, 70, 000, 000, 000, 000 miles, and42, 000, 000, 000, 000 miles. It will be observed that the differencebetween the greatest and the least of these estimates is about doublethe entire distance given by the latter. The same thing is practicallytrue of the various attempts to ascertain the distance of the otherstars which have a perceptible parallax, even those which are evidentlythe nearest. In some cases the later measures increase the distance, inother cases they diminish it; in no case is there anything like acomplete accord. Yet of course we are not to infer that it is hopelessto learn anything about the distances of the stars. With all theiruncertainties and disagreements the few parallaxes we possess have laida good foundation for a knowledge of the dimensions of at least thenearer parts of the universe. 

We find an interesting triple in psi, the magnitudes of the largercomponents being four and a half and eight and a half, distance 30". Thesmaller star has a nine-and-a-half-magnitude companion, distance 3". Amore beautiful triple is iota, magnitudes four, seven, and eight, distances 2", p. 256°, and 7. 5", p. 112°. Cassiopeia contains manystar clusters, three of which are indicated in the map. Of these 392 isperhaps the most interesting, as it includes stars of many magnitudes, among which are a red one of the eighth magnitude, and a ninth-magnitudedouble whose components are 8" apart. Not far from the star kappa wefind the spot where the most brilliant temporary star on record made itsappearance on November 11, 1572. Tycho Brahe studied this phenomenonduring the entire period of its visibility, which lasted until March, 1574. It burst out suddenly with overpowering splendor, far outshiningevery fixed star, and even equaling Venus at her brightest. In a veryshort time it began to fade, regularly diminishing in brightness, and atthe same time undergoing changes of color, ending in red, until itdisappeared. It has never been seen since, and the suspicion onceentertained that it was a variable with a period considerably exceedingthree hundred years has not been confirmed. There is a tenth-magnitudestar near the place given by Tycho as that occupied by the stranger. Many other faint stars are scattered about, however, and Tycho'smeasures were not sufficiently exact to enable us to identify theprecise position of his star. If the phenomenon was due to a collision, no reappearance of the star is to be expected. 

Camelopardalus is a very inconspicuous constellation, yet it furnishesconsiderable occupation for the telescope. Sigma 390, of magnitude five, has a companion of magnitude nine and a half, distance 15", 160°. Sigma385, also of the fifth magnitude, has a ninth-magnitude companion, distance only 2. 4", p. 160°. According to some observers, the largerstar is yellow and the smaller white. The star 1 is a very prettydouble, magnitudes both six, distance 10. 4". Its neighbor 2 of magnitudesix has an eighth-magnitude companion, distance 1. 7", p. 278°. The star7 of magnitude five is also double, the companion of magnitude eightbeing distant only 1. 2". A glance at star cluster 940, which shows aslight central condensation, completes our work in Camelopardalus, andwe turn to Ursa Major, represented in map No. 26. Here there are manyinteresting doubles and triples. Beginning with iota we find at onceoccupation for our largest glass. The magnitudes are three and ten, distance 10", p. 357°. In the double star 23 the magnitudes are four andnine, distance 23", p. 272°. A more pleasing object is sigma^2, agreenish fifth-magnitude star which has an eighth-magnitude companion, distance 2. 6", p. 245°. A good double for our four-inch glass is xi, whose magnitudes are four and five, distance 1. 87", p. 183°. This is abinary with a period of revolution of about sixty years, and isinteresting as the first binary star whose orbit was determined. Savarycalculated it in 1828. Near by is nu, a difficult double, magnitudesfour and ten and a half, distance 7", p. 147°. In 57 we find again aneasy double magnitudes six and eight, distance 5. 5", p. 4°. Anothersimilar double is 65, magnitudes six and eight, distance 3. 9", p. 38°. Athird star, magnitude seven, is seen at a distance of 114" from theprimary. 

We come now to Ursa Major's principal attraction zeta, frequently calledMizar. The naked eye perceives near it a smaller star, named Alcor. Withthe three-inch glass and a medium power we divide Mizar into two brightstars brilliantly contrasted in color, the larger being white and thesmaller blue-green. Beside Alcor, several fainter stars are seenscattered over the field of view, and, taken all in all, there are veryfew equally beautiful sights in the starry heavens. The magnitudes ofthe double are three and four, distance 14. 5", p. 148°. The large staris again double, although no telescope has been able to show it so, itsduplicity being revealed, like that of beta Aurigæ, by the periodicalsplitting of the lines in its spectrum. 

Ursa Major contains several nebulæ which may be glimpsed with telescopesof moderate dimensions. An interesting pair of these objects, both ofwhich are included in one field of view, is formed by 1949 and 1950. Thefirst named is the brighter of the two, its nucleus resembling a faintstar. The nebula 2343 presents itself to us in the form of a faint, hazystar, but with large telescopes its appearance is very singular. According to a picture made by Lord Rosse, it bears no littleresemblance to a skull, there being two symmetrically placed holes init, each of which contains a star. 

[Illustration: MAP NO. 26. ]

The portion of Canes Venatici, represented in map No. 26, contains twoor three remarkable objects. Sigma 1606 is a close double, magnitudessix and seven, distance 1", p. 336°. It is a pretty sight with thefive-inch. The double star 2 is singular in that its larger component isred and its smaller blue; magnitudes six and eight, distance 11. 4", p. 260°. Still more beautiful is 12, commonly called Cor Caroli. Thisdouble is wide, and requires but a slight magnifying power. Themagnitudes are three and six, distance 20", colors white or light yellowand blue. The nebula 3572, although we can see it only as a pair ofmisty specks, is in reality a very wonderful object. Lord Rosse'stelescope has revealed in it a complicated spiral structure, recallingthe photographs of the Andromeda nebula, and indicating that stupendouschanges must be in process within it, although our records ofobservation are necessarily too brief to bring out any perceptiblealteration of figure. It would seem that the astronomer has, of all men, the best reasons for complaining of the brevity of human life. 

Lastly, we turn to Ursa Minor and the Pole Star. The latter is acelebrated double, not difficult, except with a telescope of less thanthree inches aperture in the hands of an inexperienced observer. Themagnitudes are two and nine, distance 18. 5". The small star has a dullblue color. In 1899 it was discovered by spectroscopic evidence that thePole Star is triple. In pi' we see a wide double, magnitudes six andseven, distance 30", p. 83°. 

This completes our survey of the starry heavens. 

CHAPTER VIII

SCENES ON THE PLANETS

 "These starry globes far surpassed the earth in grandeur, and the latter looked so diminutive that our empire, which appeared only as a point on its surface, awoke my pity. "--CICERO, THE DREAM OF SCIPIO. 

Although amateurs have played a conspicuous part in telescopic discoveryamong the heavenly bodies, yet every owner of a small telescope shouldnot expect to attach his name to a star. But he certainly can dosomething perhaps more useful to himself and his friends; he can followthe discoveries that others, with better appliances and opportunities, have made, and can thus impart to those discoveries that sense ofreality which only comes from seeing things with one's own eyes. Thereare hundreds of things continually referred to in books and writings onastronomy which have but a misty and uncertain significance for the merereader, but which he can easily verify for himself with the aid of atelescope of four or five inches aperture, and which, when actuallyconfronted by the senses, assume a meaning, a beauty, and an importancethat would otherwise entirely have escaped him. Henceforth everyallusion to the objects he has seen is eloquent with intelligence andsuggestion. 

Take, for instance, the planets that have been the subject of so manyobservations and speculations of late years--Mars, Jupiter, Saturn, Venus. For the ordinary reader much that is said about them makes verylittle impression upon his mind, and is almost unintelligible. He readsof the "snow patches" on Mars, but unless he has actually seen thewhitened poles of that planet he can form no clear image in his mind ofwhat is meant. So the "belts of Jupiter" is a confusing and misleadingphrase for almost everybody except the astronomer, and the rings ofSaturn are beyond comprehension unless they have actually been seen. 

It is true that pictures and photographs partially supply the place ofobservation, but by no means so successfully as many imagine. The mostrealistic drawings and the sharpest photographs in astronomy are thoseof the moon, yet I think nobody would maintain that any picture inexistence is capable of imparting a really satisfactory visualimpression of the appearance of the lunar globe. Nobody who has not seenthe moon with a telescope--it need not be a large one--can form acorrect and definite idea of what the moon is like. 

The satisfaction of viewing with one's own eyes some of the things theastronomers write and talk about is very great, and the illuminationthat comes from such viewing is equally great. Just as in foreign travelthe actual seeing of a famous city, a great gallery filled withmasterpieces, or a battlefield where decisive issues have been foughtout illuminates, for the traveler's mind, the events of history, thecriticisms of artists, and the occurrences of contemporary life inforeign lands, so an acquaintance with the sights of the heavens gives agrasp on astronomical problems that can not be acquired in any otherway. The person who has been in Rome, though he may be no archæologist, gets a far more vivid conception of a new discovery in the Forum thandoes the reader who has never seen the city of the Seven Hills; and theamateur who has looked at Jupiter with a telescope, though he may be noastronomer, finds that the announcement of some change among thewonderful belts of that cloudy planet has for him a meaning and aninterest in which the ordinary reader can not share. 

[Illustration: JUPITER SEEN WITH A FIVE-INCH TELESCOPE. 

Shadow of a satellite visible. ]

Jupiter is perhaps the easiest of all the planets for the amateurobserver. A three-inch telescope gives beautiful views of the greatplanet, although a four-inch or a five-inch is of course better. Butthere is no necessity for going beyond six inches' aperture in any case. For myself, I should care for nothing better than my Byrne five-inch offifty-two inches' focal distance. With such a glass more details arevisible in the dark belts and along the bright equatorial girdle thancan be correctly represented in a sketch before the rotation of theplanet has altered their aspect, while the shadows of the satellitesthrown upon the broad disk, and the satellites themselves when intransit, can be seen sometimes with exquisite clearness. The contrastingcolors of various parts of the disk are also easily studied with a glassof four or five inches' aperture. 

There is a charm about the great planet when he rides high in a clearevening sky, lording it over the fixed stars with his serene, unflickering luminousness, which no possessor of a telescope can resist. You turn the glass upon him and he floats into the field of view, withhis _cortége_ of satellites, like a yellow-and-red moon, attended byfour miniatures of itself. You instantly comprehend Jupiter's masteryover his satellites--their allegiance is evident. No one would for aninstant mistake them for stars accidentally seen in the same field ofview. Although it requires a very large telescope to magnify their disksto measurable dimensions, yet the smallest glass differentiates them atonce from the fixed stars. There is something almost startling in theirappearance of companionship with the huge planet--this suddenverification to your eyes of the laws of gravitation and of centralforces. It is easy, while looking at Jupiter amid his family, tounderstand the consternation of the churchmen when Galileo's telescoperevealed that miniature of the solar system, and it is gratifying togaze upon one of the first battle grounds whereon science gained adecisive victory for truth. 

The swift changing of place among the satellites, as well as therapidity of Jupiter's axial rotation, give the attraction of visiblemovement to the Jovian spectacle. The planet rotates in four or fiveminutes less than ten hours--in other words, it makes two turns and fourtenths of a third turn while the earth is rolling once upon its axis. Apoint on Jupiter's equator moves about twenty-seven thousand miles, orconsiderably more than the entire circumference of the earth, in asingle hour. The effect of this motion is clearly perceptible to theobserver with a telescope on account of the diversified markings andcolors of the moving disk, and to watch it is one of the greatestpleasures that the telescope affords. 

It would be possible, when the planet is favorably situated, to witnessan entire rotation of Jupiter in the course of one night, but thebeginning and end of the observation would be more or less interferedwith by the effects of low altitude, to say nothing of the tedium of solong a vigil. But by looking at the planet for an hour at a time in thecourse of a few nights every side of it will have been presented toview. Suppose the first observation is made between nine and ten o'clockon any night which may have been selected. Then on the following nightbetween ten and eleven o'clock Jupiter will have made two and a halfturns upon his axis, and the side diametrically opposite to that seen onthe first night will be visible. On the third night between eleven andtwelve o'clock Jupiter will have performed five complete rotations, andthe side originally viewed will be visible again. 

Owing to the rotundity of the planet, only the central part of the diskis sharply defined, and markings which can be easily seen when centrallylocated become indistinct or disappear altogether when near the limb. Approach to the edge of the disk also causes a foreshortening whichsometimes entirely alters the aspect of a marking. It is advisable, therefore, to confine the attention mainly to the middle of the disk. Astime passes, clearly defined markings on or between the cloudy beltswill be seen to approach the western edge of the disk, gradually losingtheir distinctness and altering their appearance, while from the regionof indistinct definition near the eastern edge other markings slowlyemerge and advance toward the center, becoming sharper in outline andmore clearly defined in color as they swing into view. 

Watching these changes, the observer is carried away by the reflectionthat he actually sees the turning of another distant world upon its axisof rotation, just as he might view the revolving earth from a standpointon the moon. Belts of reddish clouds, many thousands of miles across, are stretched along on each side of the equator of the great planet heis watching; the equatorial belt itself, brilliantly lemon-hued, orsometimes ruddy, is diversified with white globular and balloon-shapedmasses, which almost recall the appearance of summer cloud domes hangingover a terrestrial landscape, while toward the poles shadowy expanses ofgradually deepening blue or blue-gray suggest the comparative coolnessof those regions which lie always under a low sun. 

[Illustration: ECLIPSES AND TRANSITS OF JUPITER'S SATELLITES. 

Satellite I and the shadow of III are seen in transit. IV is about to beeclipsed. ]

After a few nights' observation even the veriest amateur finds himselfrecognizing certain shapes or appearances--a narrow dark belt runningslopingly across the equator from one of the main cloud zones to theother, or a rift in one of the colored bands, or a rotund white massapparently floating above the equator, or a broad scallop in the edge ofa belt like that near the site of the celebrated "red spot, " whosechanges of color and aspect since its first appearance in 1878, togetherwith the light it has thrown on the constitution of Jupiter's disk, haveall but created a new Jovian literature, so thoroughly and so frequentlyhave they been discussed. 

And, having noticed these recurring features, the observer will begin tonote their relations to one another, and will thus be led to observethat some of them gradually drift apart, while others drift nearer; andafter a time, without any aid from books or hints from observatories, hewill discover for himself that there is a law governing the movements onJupiter's disk. Upon the whole he will find that the swiftest motionsare near the equator, and the slowest near the poles, although, if he ispersistent and has a good eye and a good instrument, he will noteexceptions to this rule, probably arising, as Professor Hough suggests, from differences of altitude in Jupiter's atmosphere. Finally, he willconclude that the colossal globe before him is, exteriorly at least, avast ball of clouds and vapors, subject to tremendous vicissitudes, possibly intensely heated, and altogether different in its physicalconstitution, although made up of similar elements, from the earth. Then, if he chooses, he can sail off into the delightful cloud-land ofastronomical speculation, and make of the striped and spotted sphere ofJove just such a world as may please his fancy--for a world of somekind it certainly is. 

For many observers the satellites of Jupiter possess even greaterattractions than the gigantic ball itself. As I have already remarked, their movements are very noticeable and lend a wonderful animation tothe scene. Although they bear classical names, they are almostuniversally referred to by their Roman numbers, beginning with theinnermost, whose symbol is I, and running outward in regular order II, III, and IV. [5] The minute satellite much nearer to the planet than anyof the others, which Mr. Barnard discovered with the Lick telescope in1892, is called the fifth, although in the order of distance it would bethe first. In size and importance, however, it can not rank with itscomparatively gigantic brothers. Of course, no amateur's telescope canafford the faintest glimpse of it. 

[5] Their names, in the same order as their numbers, are Io, Europa, Ganymede, and Callisto. 

Satellite I, situated at a mean distance of 261, 000 miles from Jupiter'scenter--about 22, 000 miles farther than the moon is from the earth--isurged by its master's overpowering attraction to a speed of 320 milesper minute, so that it performs a complete revolution in about forty-twohours and a half. The others, of course, move more slowly, but even themost distant performs its revolution in several hours less than sixteendays. The plane of their orbits is presented edgewise toward the earth, from which it follows that they appear to move back and forth nearly instraight lines, some apparently approaching the planet, while others arereceding from it. The changes in their relative positions, which can bedetected from hour to hour, are very striking night after night, andlead to a great variety of arrangements always pleasing to the eye. 

The most interesting phenomena that they present are their transits andthose of their round, black shadows across the face of the planet; theireclipses by the planet's shadow, when they disappear and afterwardreappear with astonishing suddenness; and their occultations by theglobe of Jupiter. Upon the whole, the most interesting thing for theamateur to watch is the passage of the shadows across Jupiter. Thedistinctness with which they can be seen when the air is steady islikely to surprise, as it is certain to delight, the observer. When itfalls upon a light part of the disk the shadow of a satellite is asblack and sharply outlined as a drop of ink; on a dark-colored belt itcan not so easily be seen. 

It is more difficult to see the satellites themselves in transit. Thereappears to be some difference among them as to visibility in suchcircumstances. Owing to their luminosity they are best seen when theyhave a dark belt for a background, and are least easily visible whenthey appear against a bright portion of the planet. Every observershould provide himself with a copy of the American Ephemeris for thecurrent year, wherein he will find all the information needed to enablehim to identify the various satellites and to predict, by turningWashington mean time into his own local time, the various phenomena ofthe transits and eclipses. 

While a faithful study of the phenomena of Jupiter is likely to lead thestudent to the conclusion that the greatest planet in our system is nota suitable abode for life, yet the problem of its future, alwaysfascinating to the imagination, is open; and whosoever may be disposedto record his observations in a systematic manner may at least hope torender aid in the solution of that problem. 

Saturn ranks next to Jupiter in attractiveness for the observer with atelescope. The rings are almost as mystifying to-day as they were inthe time of Herschel. There is probably no single telescopic view thatcan compare in the power to excite wonder with that of Saturn when thering system is not so widely opened but that both poles of the planetproject beyond it. One returns to it again and again with unflagginginterest, and the beauty of the spectacle quite matches its singularity. When Saturn is in view the owner of a telescope may become a recruitingofficer for astronomy by simply inviting his friends to gaze at thewonderful planet. The silvery color of the ball, delicately chased withhalf-visible shadings, merging one into another from the brightequatorial band to the bluish polar caps; the grand arch of the rings, sweeping across the planet with a perceptible edging of shadow; theirsudden disappearance close to the margin of the ball, where they gobehind it and fall straightway into night; the manifest contrast ofbrightness, if not of color, between the two principal rings; the finecurve of the black line marking the 1, 600-mile gap between theiredges--these are some of the elements of a picture that can never fadefrom the memory of any one who has once beheld it in its full glory. 

[Illustration: SATURN SEEN WITH A FIVE-INCH TELESCOPE. ]

Saturn's moons are by no means so interesting to watch as are those ofJupiter. Even the effect of their surprising number (raised to nine byProfessor Pickering's discovery in 1899 of a new one which is almost atthe limit of visibility, and was found only with the aid of photography)is lost, because most of them are too faint to be seen with ordinarytelescopes, or, if seen, to make any notable impression upon the eye. The two largest--Titan and Japetus--are easily found, and Titan isconspicuous, but they give none of that sense of companionship andobedience to a central authority which strikes even the carelessobserver of Jupiter's system. This is owing partly to their moredeliberate movements and partly to the inclination of the plane of theirorbits, which seldom lies edgewise toward the earth. 

[Illustration: POLAR VIEW OF SATURN'S SYSTEM. 

The orbits of the five nearest satellites are shown. The dotted lineoutside the rings shows Roche's limit. ]

But the charm of the peerless rings is abiding, and the interest of thespectator is heightened by recalling what science has recentlyestablished as to their composition. It is marvelous to think, whilelooking upon their broad, level surfaces--as smooth, apparently, aspolished steel, though thirty thousand miles across--that they are inreality vast circling currents of meteoritic particles or dust, throughwhich run immense waves, condensation and rarefaction succeeding oneanother as in the undulations of sound. Yet, with all their inferentialtumult, they may actually be as soundless as the depths of interstellarspace, for Struve has shown that those spectacular rings possess noappreciable mass, and, viewed from Saturn itself, their (to us) gorgeousseeming bow may appear only as a wreath of shimmering vapor spanning thesky and paled by the rivalry of the brighter stars. 

In view of the theory of tidal action disrupting a satellite within acritical distance from the center of its primary, the thoughtfulobserver of Saturn will find himself wondering what may have been theorigin of the rings. The critical distance referred to, and which isknown as Roche's limit, lies, according to the most trustworthyestimates, just outside the outermost edge of the rings. It follows thatif the matter composing the rings were collected into a single body thatbody would inevitably be torn to pieces and scattered into rings; andso, too, if instead of one there were several or many bodies ofconsiderable size occupying the place of the rings, all of these bodieswould be disrupted and scattered. If one of the present moons ofSaturn--for instance, Mimas, the innermost hitherto discovered--shouldwander within the magic circle of Roche's limit it would suffer asimilar fate, and its particles would be disseminated among the rings. One can hardly help wondering whether the rings have originated from thedemolition of satellites--Saturn devouring his children, as the ancientmyths represent, and encircling himself, amid the fury of destruction, with the dust of his disintegrated victims. At any rate, the amateurstudent of Saturn will find in the revelations of his telescope theinspirations of poetry as well as those of science, and the bent of hismind will determine which he shall follow. 

Professor Pickering's discovery of a ninth satellite of Saturn, situatedat the great distance of nearly eight million miles from the planet, serves to call attention to the vastness of the "sphere of activity"over which the ringed planet reigns. Surprising as the distance of thenew satellite appears when compared with that of our moon, it is yet farfrom the limit where Saturn's control ceases and that of the sun becomespredominant. That limit, according to Prof. Asaph Hall's calculation, isnearly 30, 000, 000 miles from Saturn's center, while if our moon wereremoved to a distance a little exceeding 500, 000 miles the earth wouldbe in danger of losing its satellite through the elopement of Artemiswith Apollo. 

Although, as already remarked, the satellites of Saturn are notespecially interesting to the amateur telescopist, yet it may be well tomention that, in addition to Titan and Japetus, the satellite namedRhea, the fifth in order of distance from the planet, is not a difficultobject for a three-or four-inch telescope, and two others considerablyfainter than Rhea--Dione (the fourth) and Tethys (the third)--may beseen in favorable circumstances. The others--Mimas (the first), Enceladus (the second), and Hyperion (the seventh)--are beyond the reachof all but large telescopes. The ninth satellite, which has received thename of Ph[oe]be, is much fainter than any of the others, its stellarmagnitude being reckoned by its discoverer at about 15. 5. 

Mars, the best advertised of all the planets, is nearly the leastsatisfactory to look at except during a favorable opposition, like thoseof 1877 and 1892, when its comparative nearness to the earth renderssome of its characteristic features visible in a small telescope. Thenext favorable opposition will occur in 1907. 

When well seen with an ordinary telescope, say a four-or five-inchglass, Mars shows three peculiarities that may be called fairlyconspicuous--viz. , its white polar cap, its general reddish, ororange-yellow, hue, and its dark markings, one of the clearest of whichis the so-called Syrtis Major, or, as it was once named on account ofits shape, "Hourglass Sea. " Other dark expanses in the southernhemisphere are not difficult to be seen, although their outlines aremore or less misty and indistinct. The gradual diminution of the polarcap, which certainly behaves in this respect as a mass of snow and icewould do, is a most interesting spectacle. As summer advances in thesouthern hemisphere of Mars, the white circular patch surrounding thepole becomes smaller, night after night, until it sometimes disappearsentirely even from the ken of the largest telescopes. At the same timethe dark expanses become more distinct, as if the melting of the polarsnows had supplied them with a greater depth of water, or the advance ofthe season had darkened them with a heavier growth of vegetation. 

[Illustration: MARS SEEN WITH A FIVE-INCH TELESCOPE. ]

The phenomena mentioned above are about all that a small telescope willreveal. Occasionally a dark streak, which large instruments show isconnected with the mysterious system of "canals, " can be detected, butthe "canals" themselves are far beyond the reach of any telescope excepta few of the giants handled by experienced observers. The convictionwhich seems to have forced its way into the minds even of someconservative astronomers, that on Mars the conditions, to use theexpression of Professor Young, "are more nearly earthlike than on anyother of the heavenly bodies which we can see with our presenttelescopes, " is sufficient to make the planet a center of undyinginterest notwithstanding the difficulties with which the amateur isconfronted in his endeavors to see the details of its markings. 

THE ILLUMINATION OF VENUS'S ATMOSPHERE AT THE BEGINNING OF HER TRANSITACROSS THE SUN. 

In Venus "the fatal gift of beauty" may be said, as far as ourobservations are concerned, to be matched by the equally fatal gift ofbrilliance. Whether it be due to atmospheric reflection alone or to theprevalence of clouds, Venus is so bright that considerable doubt existsas to the actual visibility of any permanent markings on her surface. The detailed representations of the disk of Venus by Mr. PercivalLowell, showing in some respects a resemblance to the stripings of Mars, can not yet be accepted as decisive. More experienced astronomers thanMr. Lowell have been unable to see at all things which he draws with afearless and unhesitating pencil. That there are some shadowy featuresof the planet's surface to be seen in favourable circumstances isprobable, but the time for drawing a "map of Venus" has not yet come. 

The previous work of Schiaparelli lends a certain degree of probabilityto Mr. Lowell's observations on the rotation of Venus. This rotation, according to the original announcement of Schiaparelli, is probablyperformed in the same period as the revolution around the sun. In otherwords, Venus, if Schiaparelli and Lowell are right, always presents thesame side to the sun, possessing, in consequence, a day hemisphere and anight hemisphere which never interchange places. This condition is soantagonistic to all our ideas of what constitutes habitability for aplanet that one hesitates to accept it as proved, and almost hopes thatit may turn out to have no real existence. Venus, as the twin of theearth in size, is a planet which the imagination, warmed by its sunnyaspect, would fain people with intelligent beings a little fairer thanourselves; but how can such ideas be reconciled with the picture of aworld one half of which is subjected to the merciless rays of anever-setting sun, while the other half is buried in the fearful gloomand icy chill of unending night?

Any amateur observer who wishes to test his eyesight and his telescopein the search of shades or markings on the disk of Venus by the aid ofwhich the question of its rotation may finally be settled should do hiswork while the sun is still above the horizon. Schiaparelli adopted thatplan years ago, and others have followed him with advantage. Thediffused light of day serves to take off the glare which is so seriousan obstacle to the successful observation of Venus when seen against adark sky. Knowing the location of Venus in the sky, which can beascertained from the Ephemeris, the observer can find it by day. If histelescope is not permanently mounted and provided with "circles" thismay not prove an easy thing to do, yet a little perseverance andingenuity will effect it. One way is to find, with a star chart, somestar whose declination is the same, or very nearly the same, as that ofVenus, and which crosses the meridian say twelve hours ahead of her. Then set the telescope upon that star, when it is on the meridian atnight, and leave it there, and the next day, twelve hours after the starcrossed the meridian, look into your telescope and you will see Venus, or, if not, a slight motion of the tube will bring her into view. 

For many amateurs the phases of Venus will alone supply sufficientinterest for telescopic observation. The changes in her form, from thatof a round full moon when she is near superior conjunction to thegibbous, and finally the half-moon phase as she approaches her easternelongation, followed by the gradually narrowing and lengtheningcrescent, until she is a mere silver sickle between the sun and theearth, form a succession of delightful pictures. 

Not very much can be said for Mercury as a telescopic object. The littleplanet presents phases like those of Venus, and, according toSchiaparelli and Lowell, it resembles Venus in its rotation, keepingalways the same side to the sun. In fact, Schiaparelli's discovery ofthis peculiarity in the case of Mercury preceded the similar discoveryin the case of Venus. There are markings on Mercury which have remindedsome astronomers of the moon, and there are reasons for thinking thatthe planet can not be a suitable abode for living beings, at least forbeings resembling the inhabitants of the earth. 

Uranus and Neptune are too far away to present any attraction foramateur observers. 

CHAPTER IX

THE MOUNTAINS AND PLAINS OF THE MOON, AND THE SPECTACLES OF THE SUN

 "... The Moon, whose orbThe Tuscan artist views through optic glassAt evening from the top of Fesolé, Or in Valdarno, to descry new lands, Rivers or mountains in her spotty globe. "--PARADISE LOST. 

The moon is probably the most interesting of all telescopic objects. This arises from its comparative nearness to the earth. A telescopemagnifying 1, 000 diameters brings the moon within an apparent distanceof less than 240 miles. If telescopes are ever made with a magnifyingpower of 10, 000 diameters, then, provided that atmospheric difficultiescan be overcome, we shall see the moon as if it were only about twentymiles off, and a sensitive astronomer might be imagined to feel a littlehesitation about gazing so closely at the moon--as if he were peeringinto a neighbor world's window. 

But a great telescope and a high magnifying power are not required tointerest the amateur astronomer in the study of the moon. Our three-inchtelescope is amply sufficient to furnish us with entertainment for manyan evening while the moon is running through its phases, and we shallfind delight in frequently changing the magnifying power as we watch thelunar landscapes, because every change will present them in a differentaspect. 

It should be remembered that a telescope, unless a terrestrial eyepieceor prism is employed, reverses such an object as the moon top forbottom. Accordingly, if the moon is on or near the meridian when theobservations are made, we shall see the north polar region at the bottomand the south polar region at the top. In other words, the face of themoon as presented in the telescope will be upside down, north and southinterchanging places as compared with their positions in a geographicalmap. But east and west remain unaltered in position, as compared withsuch a map--i. E. , the eastern hemisphere of the moon is seen on theright and the western hemisphere on the left. It is the moon's westernedge that catches the first sunlight when "new moon" begins, and, as thephase increases, passing into "first quarter" and from that to "fullmoon, " the illumination sweeps across the disk from west to east. 

[Illustration: LUNAR CHART NO. 1, NORTHWEST QUARTER. ]

The narrow sickle of the new moon, hanging above the sunset, is acharming telescopic sight. Use a low power, and observe the contrastbetween the bright, smooth round of the sunward edge, which has almostthe polish of a golden rim, and the irregular and delicately shadedinner curve, where the adjacent mountains and plains picturesquelyreflect or subdue the sunshine. While the crescent grows broader newobjects are continually coming into view as the sun rises upon them, until at length one of the most conspicuous and remarkable of the lunar"seas, " the _Mare Crisium_, or Sea of Crises, lies fully displayed amidits encircling peaks, precipices, and craters. The _Mare Crisium_ is allin the sunlight between the third and fourth day after "new moon. " It isabout 350 by 280 miles in extent, and if ever filled with water musthave been a very deep sea, since its arid bed lies at a great but notprecisely ascertained depth below the general level of the moon. Thereare a few small craters on the floor of the _Mare Crisium_, the largestbearing the name of Picard, and its borders are rugged with mountains. On the southwestern side is a lofty promontory, 11, 000 feet in height, called Cape Agarum. At the middle of the eastern side a kind of bayopens deep in the mountains, whose range here becomes very narrow. Southeast of this bay lies a conspicuous bright point, the cratermountain Proclus, on which the sun has fully risen in the fourth day ofthe moon, and which reflects the light with extraordinary liveliness. Adjoining Proclus on the east and south is a curious, lozenge-shapedflat, broken with short, low ridges, and possessing a most peculiarlight-brown tint, easily distinguished from the general color tone ofthe lunar landscapes. It would be interesting to know what was passingin the mind of the old astronomer who named this singular region _PalusSomnii_. It is not the only spot on the moon which has been called a"marsh, " and to which an unexplained connection with dreams has beenascribed. 

Nearly on the same meridian with Proclus, at a distance of about ahundred miles northward, lies a fine example of a ring mountain, rathermore than forty miles in diameter, and with peak-tipped walls which insome places are 13, 000 feet in height, as measured from the floorwithin. This is Macrobius. There is an inconspicuous central mountain inthe ring. 

North of the _Mare Crisium_, and northwest of Macrobius, we find a muchlarger mountain ring, oblong in shape and nearly eighty miles in itsgreatest diameter. It is named Cleomenes. The highest point on its wallis about 10, 000 feet above the interior. Near the northeast corner ofthe wall yawns a huge and very deep crater, Tralles, while at thenorthern end is another oblong crater mountain called Burckhardt. 

From Cleomenes northward to the pole, or to the northern extremity ofthe crescent, if our observations are made during new moon, the groundappears broken with an immense number of ridges, craters, and mountainrings, among which we may telescopically wander at will. One of the moreremarkable of these objects, which may be identified with the aid ofLunar Chart No. 1, is the vast ringed plain near the edge of the disk, named Gauss. It is more than a hundred and ten miles in diameter. Owingto its situation, so far down the side of the lunar globe, it isforeshortened into a long ellipse, although in reality it is nearly acircle. A chain of mountains runs north and south across the interiorplain. Geminus, Berzelius, and Messala are other rings well worthlooking at. The remarkable pair called Atlas and Hercules demand morethan passing attention. The former is fifty-five and the latterforty-six miles in diameter. Each sinks 11, 000 feet below the summit ofthe loftiest peak on its encircling wall. Both are full of interestingdetail sufficient to occupy the careful observer for many nights. Thebroad ring bearing the name of Endymion is nearly eighty miles indiameter, and has one peak 15, 000 feet high. The interior plain is flatand dark. Beyond Endymion on the edge of the disk is part of a gloomyplain called the _Mare Humboltianum_. 

After glancing at the crater-shaped mountains on the western andsouthern border of the _Mare Crisium_, Alhazen, Hansen, Condorcet, Firmicus, etc. , we pass southward into the area covered in Lunar ChartNo. 2. The long dark plain south of the _Mare Crisium_ is the _MareFecunditatis_, though why it should have been supposed to beparticularly fecund, or fertile, is by no means clear. On the westernborder of this plain, about three hundred miles from the southern end ofthe _Mare Crisium_, is the mountain ring, or circumvallation, calledLangrenus, about ninety miles across and in places 10, 000 feet high. There is a fine central mountain with a number of peaks. Nearly ahundred miles farther south, on the same meridian, lies an equallyextensive mountain ring named Vendelinus. The broken and complicatedappearance of its northern walls will command the observer's attention. Another similar step southward, and still on the same meridian brings usto a yet finer mountain ring, slightly larger than the others, and stillmore complicated in its walls, peaks, and terraces, and in itssurroundings of craters, gorges, and broken ridges. This is Petavius. West of Petavius, on the very edge of the disk, is a wonderfulformation, a walled plain named Humboldt, which is looked down upon atone point near its eastern edge by a peak 16, 000 feet in height. About ahundred and forty miles south of Petavius is the fourth great mountainring lying on the same meridian. Its name is Furnerius. Lookparticularly at the brilliantly shining crater on the northeast slope ofthe outer wall of Furnerius. 

[Illustration: LUNAR CHART NO. 2, SOUTHWEST QUARTER. ]

Suppose that our observations are now interrupted, to be resumed whenthe moon, about "seven days old, " is in its first quarter. If we hadtime, it would be a most interesting thing to watch the advance of thelunar sunrise every night, for new beauties are displayed almost fromhour to hour; but, for the purposes of our description it is necessaryto curtail the observations. At first quarter one half of the lunarhemisphere which faces the earth is illuminated by the sun, and the lineof sunrise runs across some of the most wonderful regions of the moon. 

We begin, referring once more to Lunar Chart No. 1, in the neighborhoodof the north pole of the moon. Here the line along which day and nightmeet is twisted and broken, owing to the roughness of the lunar surface. About fifteen degrees southwest of the pole lies a remarkablesquare-cornered, mountain-bordered plain, about forty miles in length, called Barrow. Very close to the pole is a ring mountain, abouttwenty-five miles in diameter, whose two loftiest peaks, 8, 000 to 9, 000feet high, according to Neison, must, from their situation, enjoyperpetual day. 

The long, narrow, dark plain, whose nearest edge is about thirty degreessouth of the pole, is the _Mare Frigoris_, bordered on both sides byuplands and mountains. At its southern edge we find the magnificentAristoteles, a mountain ring, sixty miles across, whose immense wall iscomposed of terraces and ridges running up to lofty peaks, which risenearly 11, 000 feet above the floor of the valley. About a hundred milessouth of Aristoteles is Eudoxus, another fine mountain ring, forty milesin diameter, and quite as deep as its northern neighbor. These two makea most striking spectacle. 

We are now in the neighborhood of the greatest mountain chains on themoon, the lunar Alps lying to the east and the lunar Caucasus to thesouth of Aristoteles and Eudoxus, while still farther south, separatedfrom the Caucasus by a strait not more than a hundred miles broad, begins the mighty range of the lunar Apennines. We first turn thetelescope on the Alps. As the line of sunrise runs directly across theirhighest peaks, the effect is startling. The greatest elevations areabout 12, 000 feet. The observer's eye is instantly caught by a greatvalley, running like a furrow through the center of the mountain mass, and about eighty or ninety miles in length. The sealike expanse southand southeast of the Alps is the _Mare Imbrium_, and it is along thecoast of this so-called sea that the Alps attain their greatest height. The valley, or gorge, above mentioned, appears to cut through theloftiest mountains and to reach the "coast, " although it is so narrowedand broken among the greater peaks that its southern portion is almostlost before it actually reaches the _Mare Imbrium_. Opening wider againas it enters the _Mare_, it forms a deep bay among precipitousmountains. 

The Caucasus Mountains are not so lofty nor so precipitous as the Alps, and consequently have less attraction for the observer. They border thedark, oval plain of the _Mare Serenitatis_ on its northeastern side. Thegreat bay running out from the _Mare_ toward the northwest, between theCaucasus and the huge mountain ring of Posidonius, bears the fancifulname of _Lacus Somniorum_. In the old days when the moon was supposed tobe inhabited, those terrestrial godfathers, led by the astronomerRiccioli, who were busy bestowing names upon the "seas" and mountains ofour patient satellite, may have pleased their imagination by picturingthis arm of the "Serene Sea" as a peculiarly romantic sheet of water, amid whose magical influences the lunar gentlefolk, drifting softly intheir silver galleons and barges, and enjoying the splendors of "fullearth" poured upon their delightful little world, were accustomed tofall into charming reveries, as even we hard-headed sons of Adamoccasionally do when the waters under the keel are calm and smooth andthe balmy air of a moonlit night invokes the twin spirits of poetry andmusic. 

Posidonius, the dominating feature of the shore line here, is anextraordinary example of the many formations on the moon which are sodifferent from everything on the earth that astronomers do not find iteasy to bestow upon them names that truly describe them. It may becalled a ring mountain or a ringed plain, for it is both. Its diameterexceeds sixty miles, and the interior plain lies about 2, 000 feet belowthe outer surface of the lunar ground. The mountain wall surrounding thering is by no means remarkable for elevation, its greatest height notexceeding 6, 000 feet, but, owing to the broad sweep of the curved walls, the brightness of the plain they inclose, and the picturesqueirregularity of the silhouette of shadow thrown upon the valley floor bythe peaks encircling it, the effect produced upon the observer is verystriking and attractive. 

Having finished with Posidonius and glanced across the broken region ofthe Taurus Mountains toward the west, we turn next to consider the _MareSerenitatis_. This broad gray plain, which, with a slight magnifyingpower, certainly looks enough like a sea to justify the firsttelescopists in thinking that it might contain water, is about 430 by425 miles in extent, its area being 125, 000 square miles. Runningdirectly through its middle, nearly in a north and south line, is alight streak, which even a good opera glass shows. This streak is thelargest and most wonderful of the many similar rays which extend on allsides from the great crater, or ring, of Tycho in the southernhemisphere. The ray in question is more than 2, 000 miles long, and, likeits shorter congeners, it turns aside for nothing; neither "sea, " norpeak, nor mountain range, nor crater ring, nor gorge, nor cañon, is ableto divert it from its course. It ascends all heights and drops into alldepths with perfect indifference, but its continuity is not broken. Whenthe sun does not illuminate it at a proper angle, however, themysterious ray vanishes. Is it a metallic vein, or is it volcanic lavaor ash? Was the globe of the moon once split open along this line?

The _Mare Serenitatis_ is encircled by mountain ranges to a greaterextent than any of the other lunar "seas. " On its eastern side theCaucasus and the Apennines shut it in, except for a strait a hundredmiles broad, by means of which it is connected with the _Mare Imbrium_. On the south the range of the Hæmus Mountains borders it, on the northand northwest the Caucasus and the Taurus Mountains confine it, while onthe west, where again it connects itself by a narrow strait with another"sea, " the _Mare Tranquilitatis_, it encounters the massive uplift ofMount Argæus. Not far from the eastern strait is found the remarkablelittle crater named Linné, not conspicuous on the gray floor of the_Mare_, yet easily enough found, and very interesting because aconsiderable change of form seems to have come over this crater sometime near the middle of the nineteenth century. In referring to it as acrater it must not be forgotten that it does not form an opening in thetop of a mountain. In fact, the so-called craters on the moon, generallyspeaking, are simply cavities in the lunar surface, whose bottoms liedeep below the general level, instead of being elevated on the summit ofmountains, and inclosed in a conical peak. In regard to the allegedchange in Linné, it has been suggested, not that a volcanic eruptionbrought it about, but that a downfall of steep walls, or of anunsupported rocky floor, was the cause. The possibility of such anoccurrence, it must be admitted, adds to the interest of the observerwho regularly studies the moon with a telescope. 

Just on the southern border of the _Mare_, the beautiful ring Menelauslies in the center of the chain of the Hæmus Mountains. The ring isabout twenty miles across, and its central peak is composed of somehighly reflecting material, so that it shines very bright. The streak orray from Tycho which crosses the _Mare Serenitatis_ passes through thewalls of Menelaus, and perhaps the central peak is composed of the samesubstance that forms the ray. Something more than a hundred mileseast-southeast from Menelaus, in the midst of the dark _Mare Vaporum_, is another brilliant ring mountain which catches the eye, Manilius. Itexceeds Menelaus in brightness as well as in size, its diameter beingabout twenty-five miles. There is something singular underlying the darklunar surface here, for not only is Manilius extraordinarily brilliantin contrast with the surrounding plain, but out of that plain, aboutforty miles toward the east, projects a small mountain which is alsoremarkable for its reflecting properties, as if the gray ground wereunderlain by a stratum of some material that flashes back the sunlightwherever it is exposed. The crater mountain, Sulpicius Gallus, on theborder of the _Mare_, north of Manilius and east of Menelaus, is anotherexample of the strange shining quality of certain formations on themoon. 

Follow next the Hæmus range westward until the attention falls upon thegreat ring mountain Plinius, more than thirty miles across, and bearingan unusual resemblance to a fortification. Mr. T. G. Elger, thecelebrated English selenographer, says of Plinius that, at sunrise, "itreminds one of a great fortress or redoubt erected to command thepassage between the _Mare Tranquilitatis_ and the _Mare Serenitatis_. "But, of course, the resemblance is purely fanciful. Men, even thoughthey dwelt in the moon, would not build a rampart 6, 000 feet high!

Mount Argæus, at the southwest corner of the _Mare Serenitatis_, is avery wonderful object when the sun has just risen upon it. This occursfive days after the new moon. 

Returning to the eastern extremity of the _Mare_, we glance, in passing, at the precipitous Mount Hadley, which rises more than 15, 000 feet abovethe level of the _Mare_ and forms the northern point of the Apenninerange. Passing into the region of the _Mare Imbrium_, whose western endis divided into the _Palus Putredinis_ on the south and the _PalusNebularum_ on the north, we notice three conspicuous ring mountains, Cassini near the Alps, and Aristillus and Autolycus, a beautiful pair, nearly opposite the strait connecting the two _Maria_. Cassini isthirty-six miles in diameter, Aristillus thirty-four, and Autolycustwenty-three. The first named is shallow, only 4, 000 feet in depth fromthe highest point of its wall, while Aristillus carries some peaks onits girdle 11, 000 feet high. Autolycus, like Cassini, is of no verygreat depth. 

Westward from the middle of an imaginary line joining Aristillus andCassini is the much smaller crater Theætetus. Outside the walls of thisare a number of craterlets, and a French astronomer, Charbonneaux, ofthe Meudon Observatory, reported in December, 1900, that he hadrepeatedly observed white clouds appearing and disappearing over one ofthese small craters. 

South of the _Mare Vaporum_ are found some of the most notable of thosestrange lunar features that are called "clefts" or "rills. " Two cratermountains, in particular, are connected with them, Ariadæus at theeastern edge of the _Mare Tranquilitatis_ and Hyginus on the southernborder of the _Mare Vaporum_. These clefts appear to be broad and deepchasms, like the cañons cut by terrestrial rivers, but it can not bebelieved that the lunar cañons are the work of rivers. They are rathercracks in the lunar crust, although their bottoms are frequentlyvisible. The principal cleft from Ariadæus runs eastward and passesbetween two neighboring craters, the southern of which is namedSilberschlag, and is noteworthy for its brightness. The Hyginus cleft isbroader and runs directly through the crater ring of that name. 

The observer will find much to interest him in the great, irregular, andmuch-broken mountain ring called Julius Cæsar, as well as in the ringmountains, Godin, Agrippa, and Triesnecker. The last named, besidespresenting magnificent shadows when the sunlight falls aslant upon it, is the center of a complicated system of rills, some of which can betraced with our five-inch glass. 

We next take up Lunar Chart No. 2, and pay a telescopic visit to thesouthwestern quarter of the lunar world. The _Mare Tranquilitatis_merges through straits into two southern extensions, the _MareFecunditatis_ and the _Mare Nectaris_. The great ring mountains orringed plains, Langrenus, Vendelinus, Petavius, and Furnerius, all lyingsignificantly along the same lunar meridian, have already been noticed. Their linear arrangement and isolated position recall the row of hugevolcanic peaks that runs parallel with the shore of the Pacific Ocean inOregon and Washington--Mount Jefferson, Mount Hood, Mount St. Helen's, Mount Tacoma--but these terrestrial volcanoes, except in elevation, aremere pins' heads in the comparison. 

In the eastern part of the _Mare Fecunditatis_ lies a pair of relativelysmall craters named Messier, which possess particular interest becauseit has been suspected, though not proved, that a change of form hasoccurred in one or other of the pair. Mädler, in the first half of thenineteenth century, represented the two craters as exactly alike in allrespects. In 1855 Webb discovered that they are not alike in shape, andthat the easternmost one is the larger, and every observer easily seesthat Webb's description is correct. Messier is also remarkable for thelight streak, often said to resemble a comet's tail, which extends fromthe larger crater eastward to the shore of the _Mare Fecunditatis_. 

Goclenius and Guttemberg, on the highland between the _MareFecunditatis_ and the _Mare Nectaris_, are intersected and surrounded byclefts, besides being remarkable for their broken and irregular thoughlofty walls. Guttemberg is forty-five miles and Goclenius twenty-eightmiles in diameter. The short mountain range just east of Guttemberg, andbordering a part of the _Mare Nectaris_ on the west, is called thePyrenees. 

The _Mare Nectaris_, though offering in its appearance no explanation ofits toothsome name--perhaps it was regarded as the drinking cup of theOlympian gods--is one of the most singular of the dark lunar plains inits outlines. At the south it ends in a vast semicircular bay, sixtymiles across, which is evidently a half-submerged mountain ring. Butsubmerged by what? Not water, but perhaps a sea of lava which has nowsolidified and forms the floor of the _Mare Nectaris_. The name of thissingular formation is Fracastorius. Elger has an interesting remarkabout it. 

"On the higher portion of the interior, near the center, " he says, "is acurious object consisting apparently of four light spots, arranged in asquare, with a craterlet in the middle, all of which undergo notablechanges of aspect under different phases. "

Other writers also call attention to the fine markings, minutecraterlets, and apparently changeable spots on the floor ofFracastorius. 

We go now to the eastern side of the _Mare Nectaris_, where we find oneof the most stupendous formations in the lunar world, the great mountainring of Theophilus, noticeably regular in outline and perfect in thecompleteness of its lofty wall. The circular interior, which contains inthe center a group of mountains, one of whose peaks is 6, 000 feet high, sinks 10, 000 feet below the general level of the moon outside the wall!One of the peaks on the western edge towers more than 18, 000 feet abovethe floor within, while several other peaks attain elevations of 15, 000to 16, 000 feet. The diameter of the immense ring, from crest to crest ofthe wall, is sixty-four miles. Theophilus is especially wonderful on thefifth and sixth days of the moon, when the sun climbs its shiningpinnacles and slowly discloses the tremendous chasm that lies within itscircles of terrible precipices. 

On the southeast Theophilus is connected by extensions of its walls witha shattered ring of vast extent called Cyrillus; and south fromCyrillus, and connected with the same system of broken walls, lies thestill larger ring named Catharina, whose half-ruined walls and numerouscrater pits present a fascinating spectacle as the shadows retreatbefore the sunrise advancing across them. These three--Theophilus, Cyrillus, and Catharina--constitute a scene of surpassing magnificence, a glimpse of wonders in another world sufficient to satisfy the mostriotous imagination. 

South of the _Mare Nectaris_ the huge ring mountain of Piccolominiattracts attention, its massive walls surrounding a floor nearly sixtymiles across, and rising in some places to an altitude of nearly 15, 000feet. It should be understood that wherever the height of the mountainwall of such a ring is mentioned, the reference level is that of theinterior plain or floor. The elevation, reckoned from the outer side, isalways very much less. 

The entire region south and east of Theophilus and its great neighborsis marvelously rough and broken. Approaching the center of the moon, wefind a system of ringed plains even greater in area than any of those wehave yet seen. Hipparchus is nearly a hundred miles long from north tosouth, and nearly ninety miles broad from east to west. But its wallshave been destroyed to such an extent that, after all, it yields ingrandeur to a formation like Theophilus. 

Albategnius is sixty-five miles across, with peaks from 10, 000 to 15, 000feet in height. Sacrobosco is a confused mass of broken and distortedwalls. Aliacensis is remarkable for having a peak on the eastern side ofits wall which is more than 16, 000 feet high. Werner, forty-five milesin diameter, is interesting because under its northeastern wall Mädler, some seventy years ago, saw a light spot of astonishing brightness, unmatched in that respect by anything on the moon except the peak ofAristarchus, which we shall see later. This spot seems afterward to havelost brilliance, and the startling suggestion has been made that itsoriginal brightness might have been due to its then recent deposit froma little crater that lies in the midst of it. Walter is of giganticdimensions, about one hundred miles in diameter. Unlike the majority ofthe ringed plains, it departs widely from a circle. Stöfler is yetlarger than Walter; but most interesting of all these giganticformations is Maurolycus, whose diameter exceeds one hundred and fiftymiles, and which has walls 13, 000 or 14, 000 feet high. Yet, astonishingthough it may seem, this vast and complicated mass of mountain walls, craters, and peaks, is virtually unseen at full moon, owing to theperpendicularity of the sunlight, which prevents the casting of shadows. 

We shall next suppose that another period of about seven days haselapsed, the moon in the meantime reaching its full phase. We refer forguidance to Lunar Chart No. 3. The peculiarity of the northeasternquadrant which immediately strikes the eye is the prevalence of thebroad plains called _Maria_, or "seas. " The northern and central partsare occupied by the _Mare Imbrium_, the "Sea of Showers" or of "Rains, "with its dark bay the _Sinus Æstuum_, while the eastern half is coveredby the vast _Oceanus Procellarum_, the "Ocean of Storms" or of"Tempests. "

Toward the north a conspicuous oval, remarkably dark in hue, immediatelyattracts our attention. It is the celebrated ringed plain of Plato, about sixty miles in diameter and surrounded by a saw-edged rampart, some of whose pinnacles are 6, 000 or 7, 000 feet high. Plato is afavorite subject for study by selenographers because of the changes ofcolor which its broad, flat floor undergoes as the sun rises upon it, and also because of the existence of enigmatical spots and streaks whosevisibility changes. South of Plato, in the _Mare Imbrium_, rises aprecipitous, isolated peak called Pico, 8, 000 feet in height. Itsresemblance in situation to the conical mountain Pico in the Azoresstrikes the observer. 

[Illustration: LUNAR CHART NO. 3, NORTHEAST QUARTER. ]

Eastward of Plato a line of highlands, separating the _Mare Imbrium_from the _Mare Frigoris, _ carries the eye to the beautiful semicircular_Sinus Iridum_, or "Bay of Rainbows. " The northwestern extremity ofthis remarkable bay is guarded by a steep and lofty promontory calledCape Laplace, while the southeastern extremity also has its toweringguardian, Cape Heraclides. The latter is interesting for showing, between nine and ten days after full moon, a singularly perfect profileof a woman's face looking out across the _Mare Imbrium_. The windinglines, like submerged ridges, delicately marking the floor of the _SinusIridum_ and that of the _Mare_ beyond, are beautiful telescopicobjects. The "bay" is about one hundred and thirty-five miles long byeighty-four broad. 

The _Mare Imbrium_, covering 340, 000 square miles, is sparingly dottedover with craters. All of the more conspicuous of them are indicated inthe chart. The smaller ones, like Caroline Herschel, Helicon, Leverrier, Délisle, etc. , vary from eight to twelve miles in diameter. Lambert isseventeen miles in diameter, and Euler nineteen, while Timocharis istwenty-three miles broad and 7, 000 feet deep below its walls, which riseonly 3, 000 feet above the surface of the _Mare_. 

Toward the eastern border of the sea, south of the Harbinger Mountains, we find a most remarkable object, the mountain ring, or crater plain, called Aristarchus. This ring is not quite thirty miles in diameter, butthere is nothing on the moon that can compare with it in dazzlingbrilliance. The central peak, 1, 200 or 1, 300 feet high, gleams like amountain of crusted snow, or as if it were composed of a mass offresh-broken white metal, or of compacted crystals. Part of the innerslope of the east wall is equally brilliant. In fact, so much light ispoured out of the circumvallation that the eye is partially blinded, andunable distinctly to see the details of the interior. No satisfactoryexplanation of the extraordinary reflecting power of Aristarchus hasever been offered. Its neighbor toward the east, Herodotus, is somewhatsmaller and not remarkably bright, but it derives great interest fromthe fact that out of a breach in its northern wall issues a vast cleft, or chasm, which winds away for nearly a hundred miles across the floorof the _Mare_, making an abrupt turn when it reaches the foot of theHarbinger Mountains. 

The comparatively small crater, Lichtenberg, near the northeastern limbof the moon, is interesting because Mädler used to see in itsneighborhood a pale-red tint which has not been noticed since his day. 

Returning to the western side of the quadrant represented in Lunar ChartNo. 3, we see the broad and beautifully regular ringed plain ofArchimedes, fifty miles in diameter and 4, 000 feet deep. 

A number of clefts extend between the mountainous neighborhood ofArchimedes and the feet of the gigantic Apennine Mountains on thesouthwest. The little double crater, Beer, between Archimedes andTimocharis, is very bright. 

The Apennines extend about four hundred and eighty miles in anorthwesterly and southeasterly direction. One of their peaks near thesouthern end of the range, Mount Huygens, is at least 18, 000 feet high, and the black silhouettes of their sharp-pointed shadows thrown upon thesmooth floor of the _Mare Imbrium_ about the time of first quarterpresent a spectacle as beautiful as it is unique. The Apennines end atthe southeast in the ring mountain, Eratosthenes, thirty-eight milesacross and very deep, one of its encircling chain of peaks rising 16, 000feet above the floor, and about half that height above the level of the_Mare Imbrium_. The shadows cast by Eratosthenes at sunrise aremagnificent. 

And now we come to one of the supreme spectacles of the moon, theimmense ring or crater mountain Copernicus. This is generally regardedas the grandest object that the telescope reveals on the earth'ssatellite. It is about fifty-six miles across, and its interior falls toa depth of 8, 000 feet below the _Mare Imbrium_. Its broad wall, composedof circle within circle of ridges, terraces, and precipices, rises onthe east about 12, 000 feet above the floor. On the inner side the slopesare very steep, cliff falling below cliff, until the bottom of thefearful abyss is attained. To descend those precipices and reach thedepressed floor of Copernicus would be a memorable feat for amountaineer. In the center of the floor rises a complicated mountainmass about 2, 400 feet high. All around Copernicus the surface of themoon is dotted with countless little crater pits, and splashed withwhitish streaks. Northward lie the Carpathian Mountains, terminating onthe east in Tobias Mayer, a ring mountain more than twenty miles across. The mountain ring Kepler, which is also the center of a great system ofwhitish streaks and splashes, is twenty-two miles in diameter, andnotably brilliant. 

Finally, we turn to the southeastern quadrant of the moon, representedin Lunar Chart No. 4. The broad, dark expanse extending from the northis the _Mare Nubium_ on the west and the _Oceanus Procellarum_ on theeast. Toward the southeast appears the notably dark, rounded area of the_Mare Humorum_ inclosed by highlands and rings. We begin with the rangeof vast inclosures running southward near the central meridian, andstarting with Ptolemæus, a walled plain one hundred and fifteen miles inits greatest diameter and covering an area considerably exceeding thatof the State of Massachusetts. Its neighbor toward the south, Alphonsus, is eighty-three miles across. Next comes Arzachel, more than sixty-fivemiles in diameter. Thebit, more than thirty miles across, is very deep. East of Thebit lies the celebrated "lunar railroad, " a straight, isolated wall about five hundred feet high and sixty-five miles long, dividing at its southern end into a number of curious branches, formingthe buttresses of a low mountain. Purbach is sixty miles broad, andsouth of that comes a wonderful region where the ring mountains Hell, Ball, Lexell, and others, more or less connected with walls, inclose anarea even larger than Ptolemæus, but which, not being so distinctlybordered as some of the other inclosed plains, bears no distinctivename. 

[Illustration: LUNAR CHART NO. 4, SOUTHEAST QUARTER. ]

The next conspicuous object toward the south ranks with Copernicus amongthe grandest of all lunar phenomena--the ring, or crater, Tycho. It isabout fifty-four miles in diameter and some points on its wall rise17, 000 feet above the interior. In the center is a bright mountain peak5, 000 feet high. But wonderful as are the details of its mountain ring, the chief attraction of Tycho is its manifest relation to the mysteriousbright rays heretofore referred to, which extend far across the surfaceof the moon in all directions, and of which it is the center. Thestreaks about Copernicus are short and confused, constituting rather asplash than a regular system of rays; but those emanating from Tycho arevery long, regular, comparatively narrow, and form arcs of great circleswhich stretch away for hundreds of miles, allowing no obstacle tointerrupt their course. 

Southwest of Tycho lies the vast ringed plain of Maginus, a hundredmiles broad and very wonderful to look upon, with its labyrinth offormations, when the sun slopes across it, and yet, like Maurolycus, invisible under a vertical illumination. "The full moon, " to useMädler's picturesque expression, "knows no Maginus. " Still larger andyet more splendid is Clavius, which exceeds one hundred and forty milesin diameter and covers 16, 000 square miles of ground within its fringingwalls, which carry some of the loftiest peaks on the moon, severalattaining 17, 000 feet. The floor is deeply depressed, so that aninhabitant of this singular inclosure, larger than Massachusetts, Connecticut, and Rhode Island combined, would dwell in land sunk twomiles below the general level of the world about him. 

In the neighborhood of the south pole lies the large walled plain ofNewton, whose interior is the deepest known depression on the moon. Itis so deep that the sunshine never touches the larger part of the floorof the inner abyss, and a peak on its eastern wall rises 24, 000 feetsheer above the tremendous pit. Other enormous walled plains areLongomontanus, Wilhelm I, Schiller, Bailly, and Schickard. The latter isone hundred and thirty-four miles long and bordered by a ring varyingfrom 4, 000 to 9, 000 feet in height. Wargentin, the oval close to themoon's southeast limb, beyond Schickard, is a unique formation in that, instead of its interior being sunk below the general level, it iselevated above it. It has been suggested that this peculiarity is due tothe fact that the floor of Wargentin was formed by inflation from below, and that it has cooled and solidified in the shape of a gigantic domearched over an immense cavity beneath. A dome of such dimensions, however, could not retain its form unless partly supported from beneath. 

Hainzel is interesting from its curious outline; Cichus for the hugeyawning crater on its eastern wall; Capuanus for a brilliant shiningcrater also on its eastern wall; and Mercator for possessing brightcraters on both its east and its west walls. Vitello has a brightcentral mountain and gains conspicuousness from its position at the edgeof the dark _Mare Humorum_. Agatharchides is the broken remnant of agreat ring mountain. Gassendi, an extremely beautiful object, is aboutfifty-five miles across. It is encircled with broken walls, craters andbright points, and altogether presents a very splendid appearance aboutthe eleventh day of the moon's age. 

Letronne is a half-submerged ring, at the southern end of the _OceanusProcellarum_, which recalls Fracastorius in the western lunarhemisphere. It lies, however, ten degrees nearer the equator thanFracastorius. Billy is a mountain ring whose interior seems to have beensubmerged by the dark substance of the _Oceanus Procellarum_, althoughits walls have remained intact. Mersenius is a very conspicuous ring, forty miles in diameter, east of the _Mare Humorum_. Vieta, fifty milesacross, is also a fine object. Grimaldi, a huge dusky oval, is nearlyone hundred and fifty miles in its greatest length. The ring mountainLandsberg, on the equator, and near the center of the visible easternhemisphere, is worth watching because Elger noticed changes of color inits interior in 1888. 

Bullialdus, in the midst of the _Mare Nubium_, is a very conspicuous andbeautiful ring mountain about thirty-eight miles in diameter, with walls8, 000 feet high above the interior. 

Those who wish to see the lunar mountains in all their varying aspectswill not content themselves with views obtained during the advance ofthe sunlight from west to east, between "new moon" and "full moon, " butwill continue their observations during the retreat of the sunlight fromeast to west, after the full phase is passed. 

It is evident that the hemisphere of the moon which is forever turnedaway from the earth is quite as marvelous in its features as the partthat we see. It will be noticed that the entire circle of the moon'slimb, with insignificant interruptions, is mountainous. Possibly theinvisible side of our satellite contains yet grander peaks and cratermountains than any that our telescopes can reach. This probability isincreased by the fact that the loftiest known mountain on the moon isnever seen except in silhouette. It is a member of a great chain thatbreaks the lunar limb west of the south pole, and that is called theLeibnitz Mountains. The particular peak referred to is said by someauthorities to exceed 30, 000 feet in height. Other great ranges seenonly in profile are the Dörfel Mountains on the limb behind the ringplain Bailly, the Cordilleras, east of Eichstadt, and the D'AlembertMountains beyond Grimaldi. The profile of these great mountains isparticularly fine when they are seen during an eclipse of the sun. Then, with the disk of the sun for a background, they stand out with startlingdistinctness. 

THE SUN

When the sun is covered with spots it becomes a most interesting objectfor telescopic study. Every amateur's telescope should be provided withapparatus for viewing the sun. A dark shade glass is not sufficient andnot safe. What is known as a solar prism, consisting of two solid prismsof glass, cemented together in a brass box which carries a short tubefor the eyepiece, and reflecting an image of the sun from their plane ofjunction--while the major remnant of light and heat passes directlythrough them and escapes from an opening provided for thepurpose--serves very well. Better and more costly is an apparatus calleda helioscope, constructed on the principle of polarization and providedwith prisms and reflectors which enable the observer, by properadjustment, to govern very exactly and delicately the amount of lightthat passes into the eyepiece. 

Furnished with an apparatus of this description we can employ either athree-, four-, or five-inch glass upon the sun with much satisfaction. For the amateur's purposes the sun is only specially interesting when itis spotted. The first years of the twentieth century will behold agradual growth in the number and size of the solar spots as those yearshappen to coincide with the increasing phase of the sun-spot period. Large sun spots and groups of spots often present an immense amount ofdetail which tasks the skill of the draughtsman to represent it. But alittle practice will enable one to produce very good representations ofsun spots, as well as of the whitish patches called faculæ by which theyare frequently surrounded. 

For the simple purpose of exhibiting the spotted face of the sun withoutmuch magnifying power, a telescope may be used to project the solarimage on a white sheet or screen. If the experiment is tried in a room, a little ingenuity will enable the observer to arrange a curtaincovering the window used, in such a way as to exclude all the lightexcept that which comes through the telescope. Then, by placing a sheetof paper or a drawing board before the eyepiece and focusing the imageof the sun upon it, very good results may be obtained. 

If one has a permanent mounting and a driving clock, a smallspectroscope may be attached, for solar observations, even to atelescope of only four or five inches aperture, and with its aid mostinteresting views may be obtained of the wonderful red hydrogen flamesthat frequently appear at the edge of the solar disk. 

CHAPTER X

ARE THERE PLANETS AMONG THE STARS?

 "... And if there should beWorlds greater than thine own, inhabitedBy greater things, and they themselves far moreIn number than the dust of thy dull earth, What wouldst thou think?"--BYRON'S CAIN. 

This always interesting question has lately been revived in a startlingmanner by discoveries that have seemed to reach almost deep enough totouch its solution. The following sentences, from the pen of Dr. T. J. J. See, of the Lowell Observatory, are very significant from this pointof view:

"Our observations during 1896-'97 have certainly disclosed stars moredifficult than any which astronomers had seen before. Among theseobscure objects about half a dozen are truly wonderful, in that theyseem to be dark, almost black in color, and apparently are shining by adull reflected light. It is unlikely that they will prove to beself-luminous. If they should turn out dark bodies in fact, shining onlyby the reflected light of the stars around which they revolve, we shouldhave the first case of planets--dark bodies--noticed among the fixedstars. "

Of course, Dr. See has no reference in this statement to the immensedark bodies which, in recent years, have been discovered byspectroscopic methods revolving around some of the visible stars, although invisible themselves. The obscure objects that he describesbelong to a different class, and might be likened, except perhaps inmagnitude, to the companion of Sirius, which, though a light-givingbody, exhibits nevertheless a singular defect of luminosity in relationto its mass. Sirius has only twice the mass, but ten thousand times theluminosity, of its strange companion! Yet the latter is evidently rathera faint, or partially extinguished, sun than an opaque body shining onlywith light borrowed from its dazzling neighbor. The objects seen by Dr. See, on the contrary, are "apparently shining by a dull reflectedlight. "

If, however (as he evidently thinks is probable), these objects shouldprove to be really non-luminous, it would not follow that they are to beregarded as more like the planets of the solar system than like the darkcompanions of certain other stars. A planet, in the sense which weattach to the word, can not be comparable in mass and size with the sunaround which it revolves. The sun is a thousand times larger than thegreatest of its attendant planets, Jupiter, and more than a milliontimes larger than the earth. It is extremely doubtful whether therelation of sun and planet could exist between two bodies of anythinglike equal size, or even if one exceeded the other many times inmagnitude. It is only when the difference is so great that the smallerof the two bodies is insignificant in comparison with the larger, thatthe former could become a cool, life-bearing globe, nourished by thebeneficent rays of its organic comrade and master. 

Judged by our terrestrial experience, which is all we have to go by, themagnitude of a planet, if it is to bear life resembling that of theearth, is limited by other considerations. Even Jupiter, which, as faras our knowledge extends, represents the extreme limit of greatplanetary size, may be too large ever to become the abode of livingbeings of a high organization. The force of gravitation on the surfaceof Jupiter exceeds that on the earth's surface as 2. 64 to 1. Considering the effects of this on the weight and motion of bodies, thedensity of the atmosphere, etc. , it is evident that Jupiter would, tosay the very least, be an exceedingly uncomfortable place of abode forbeings resembling ourselves. But Jupiter, if it is ever to become asolid, rocky globe like ours, must shrink enormously in volume, sinceits density is only 0. 24 as compared with the earth. Now, the surfacegravity of a planet depends on its mass and its radius, being directlyas the former and inversely as the square of the latter. But inshrinking Jupiter will lose none of its mass, although its radius willbecome much smaller. The force of gravity will consequently increase onits surface as the planet gets smaller and more dense. 

The present mean diameter of Jupiter is 86, 500 miles, while its massexceeds that of the earth in the ratio of 316 to 1. Suppose Jupitershrunk to three quarters of its present diameter, or 64, 800 miles, thenits surface gravity would exceed the earth's nearly five times. With onehalf its present diameter the surface gravity would become more than tentimes that of the earth. On such a planet a man's bones would snapbeneath his weight, even granting that he could remain upright at all!It would seem, then, that, unless we are to abandon terrestrialanalogies altogether and "go it blind, " we must set an upper limit tothe magnitude of a habitable planet, and that Jupiter represents suchupper limit, if, indeed, he does not transcend it. 

The question then becomes, Can the faint objects seen by Dr. See and hisfellow-observers, in the near neighborhood of certain stars, be planetsin the sense just described, or are they necessarily far greater inmagnitude than the largest planet, in the accepted sense of that word, which can be admitted into the category--viz. , the planet Jupiter? Thisresolves itself into another question: At what distance would Jupiter bevisible with a powerful telescope, supposing it to receive from aneighboring star an amount of illumination not less than that which itgets from the sun? To be sure, we do not know how far away the faintobjects described by Dr. See are; but, at any rate, we can safely assumethat they are at the distance of the nearest stars, say somewhere aboutthree hundred thousand times the earth's distance from the sun. The sunitself removed to that distance would appear to our eyes only as a starof the first magnitude. But Zöllner has shown that the sun exceedsJupiter in brilliancy 5, 472, 000, 000 times. Seen from equal distances, however, the ratio would be about 218, 000, 000 to 1. This would be theratio of their light if both sun and Jupiter could be removed to aboutthe distance of the nearest stars. Since the sun would then be only asbright as one of the stars of the first magnitude, and since Jupiterwould be 218, 000, 000 times less brilliant, it is evident that the latterwould not be visible at all. The faintest stars that the most powerfultelescopes are able to show probably do not fall below the sixteenth or, at the most, the seventeenth magnitude. But a seventeenth-magnitude staris only between two and three million times fainter than the sun wouldappear at the distance above supposed, while, as we have seen, Jupiterwould be more than two hundred million times fainter than the sun. 

To put it in another way: Jupiter, at the distance of the nearest stars, would be not far from one hundred times less bright than the fainteststar which the largest telescope is just able, under the most exquisiteconditions, to glimpse. To see a star so faint as that would require anobject-glass of a diameter half as great as the length of the tube ofthe Lick telescope, or say thirty feet!

Of course, Jupiter might be more brilliantly illuminated by a brighterstar than the sun; but, granting that, it still would not be visible atsuch a distance, even if we neglect the well-known concealing orblinding effect of the rays of a bright star when the observer is tryingto view a faint one close to it. Clearly, then, the obscure objects seenby Dr. See near some of the stars, if they really are bodies visibleonly by light reflected from their surfaces, must be enormously largerthan the planet Jupiter, and can not, accordingly, be admitted into thecategory of planets proper, whatever else they may be. 

Perhaps they are extreme cases of what we see in the system ofSirius--i. E. , a brilliant star with a companion which has ceased toshine as a star while retaining its bulk. Such bodies may be calledplanets in that they only shine by reflected light, and that they areattached to a brilliant sun; but the part that they play in theirsystems is not strictly planetary. Owing to their great mass they bearsuch sway over their shining companions as none of our planets, nor allof them combined, can exercise; and for the same reason they can not, except in a dream, be imagined to possess that which, in our eyes, mustalways be the capital feature of a planet, rendering it in the highestdegree interesting wherever it may be found--sentient life. 

It does not follow, however, that there are no real planetary bodiesrevolving around the stars. As Dr. See himself remarks, suchinsignificant bodies as our planets could not be seen at the distance ofthe fixed stars, "even if the power of our telescopes were increased ahundredfold, and consequently no such systems are _known_. "

This brings me to another branch of the subject. In the same articlefrom which I have already quoted (Recent Discoveries respecting theOrigin of the Universe, Atlantic Monthly, vol. Lxxx, pages 484-492), Dr. See sets forth the main results of his well-known studies on theorigin of the double and multiple star systems. He finds that thestellar systems differ from the solar system markedly in two respects, which he thus describes:

 "1. The orbits are highly eccentric; on the average twelve times more elongated than those of the planets and satellites. 

 "2. The components of the stellar systems are frequently equal and always comparable in mass, whereas our satellites are insignificant compared to their planets, and the planets are equally small compared to the sun. "

These peculiarities of the star systems Dr. See ascribes to the effectof "tidal friction, " the double stars having had their birth throughfission of original fluid masses (just as the moon, according to GeorgeDarwin's theory, was born from the earth), and the reaction of tidalfriction having not only driven them gradually farther apart butrendered their orbits more and more eccentric. This manner of evolutionof a stellar system Dr. See contrasts with Laplace's hypothesis of theorigin of the planetary system through the successive separation ofrings from the periphery of the contracting solar nebula, and thegradual breaking up of those rings and their aggregation into sphericalmasses or planets. While not denying that the process imagined byLaplace may have taken place in our system, he discovers no evidence ofits occurrence among the double stars, and this leads him to thefollowing statement, in which believers in the old theological doctrinethat the earth is the sole center of mortal life and of divine carewould have found much comfort:

"It is very singular that no visible system yet discerned has anyresemblance to the orderly and beautiful system in which we live; andone is thus led to think that probably our system is unique in itscharacter. At least it is unique among all _known_ systems. "

If we grant that the solar system is the only one in which small planetsexist revolving around their sun in nearly circular orbits, then indeedwe seem to have closed all the outer universe against such beings as theinhabitants of the earth. Beyond the sun's domain only whirling stars, coupled in eccentric orbits, dark stars, some of them, but noplanets--in short a wilderness, full of all energies except those ofsentient life! This is not a pleasing picture, and I do not think we aredriven to contemplate it. Beyond doubt, Dr. See is right in concludingthat double and multiple star systems, with their components all ofmagnitudes comparable among themselves, revolving in exceedinglyeccentric orbits under the stress of mutual gravitation, bear noresemblance to the orderly system of our sun with its attendant worlds. And it is not easy to imagine that the respective members of suchsystems could themselves be the centers of minor systems of planets, onaccount of the perturbing influences to which the orbits of such minorsystems would be subjected. 

But the double and multiple stars, numerous though they be, areoutnumbered a hundred to one by the single stars which shine alone asour sun does. What reason can we have, then, for excluding these singlestars, constituting as they do the vast majority of the celestial host, from a similarity to the sun in respect to the manner of their evolutionfrom the original nebulous condition? These stars exhibit no companions, such planetary attendants as they may have lying, on account of theirminuteness, far beyond the reach of our most powerful instruments. Butsince they vastly outnumber the binary and multiple systems, and sincethey resemble the sun in having no large attendants, should we bejustified, after all, in regarding our system as "unique"? It is true wedo not know, by visual evidence, that the single stars have planets, butwe find planets attending the only representative of that class of starsthat we are able to approach closely--the sun--and we know that theexistence of those planets is no mere accident, but the result of theoperation of physical laws which must hold good in every instance ofnebular condensation. 

Two different methods are presented in which a rotating and contractingnebula may shape itself into a stellar or planetary system. The first isthat described by Laplace, and generally accepted as the probable mannerof origin of the solar system--viz. , the separation of rings from thecondensing mass, and the subsequent transformation of the rings intoplanets. The planet Saturn is frequently referred to as an instance ofthe operation of this law, in which the evolution has been arrestedafter the separation of the rings, the latter having retained the ringform instead of breaking and collecting into globes, forming in thiscase rings of meteorites, and reminding us of the comparativelyscattered rings of asteroids surrounding the sun between the orbits ofMars and Jupiter. This Laplacean process Dr. See regards astheoretically possible, but apparently he thinks that if it took placeit was confined to our system. 

The other method is that of the separation of the original rotating massinto two nearly equal parts. The mechanical possibility of such aprocess has been proved, mathematically, by Poincaré and Darwin. This, Dr. See thinks, is the method which has prevailed among the stars, andprevailed to such a degree as to make the solar system, formed by thering method, probably a unique phenomenon in the universe. 

Is it not more probable that both methods have been in operation, andthat, in fact, the ring method has operated more frequently than theother? If not, why do the single stars so enormously outnumber thedouble ones? It is of the essence of the fission process that theresulting masses should be comparable in size. If, then, that processhas prevailed in the stellar universe to the practical exclusion of theother, there should be very few single stars; whereas, as a matter offact, the immense majority of the stars are single. And, rememberingthat the sun viewed from stellar distances would appear unattended bysubsidiary bodies, are we not justified in concluding that its origin isa type of the origin of the other single stars?

While it is, as I have remarked, of the essence of the fission processthat the resulting parts of the divided mass should be comparable inmagnitude, it is equally of the essence of the ring, or Laplaceanprocess, that the bodies separated from the original mass should becomparatively insignificant in magnitude. 

As to the coexistence of the two processes, we have, perhaps, an examplein the solar system itself. Darwin's demonstration of the possible birthof the moon from the earth, through fission and tidal friction, does notapply to the satellites attending the other planets. The moon isrelatively a large body, comparable in that respect with the earth, while the satellites of Jupiter and Saturn, for instance, are relativelysmall. But in the case of Saturn there is visible evidence that the ringprocess of satellite formation has prevailed. The existing rings havenot broken up, but their very existence is a testimony of the origin ofthe satellites exterior to them from other rings which did break up. Thus we need not go as far away as the stars in order to find instancesillustrating both the methods of nebular evolution that we have beendealing with. 

The conclusion, then, seems to be that we are not justified in assumingthat the solar system is unique simply because it differs widely fromthe double and multiple star systems; and that we should rather regardit as probable that the vast multitude of stars which do not appear, when viewed with the telescope, or studied by spectroscopic methods, tohave any attendants comparable with themselves in magnitude, haveoriginated in a manner resembling that of the sun's origin, and may bethe centers of true planetary systems like ours. The argument, I think, goes further than to show the mere possibility of the existence of suchplanetary systems surrounding the single stars. If those stars did notoriginate in a manner quite unlike the origin of the sun, then theexistence of planets in their neighborhood is almost a foregoneconclusion, for the sun could hardly have passed through the process offormation out of a rotating nebula without evolving planets during itscontraction. And so, notwithstanding the eccentricities of the doublestars, we may still cherish the belief that there are eyes to see andminds to think out in celestial space. 

INDEX

NOTE. --Double, triple, multiple, and colored stars, star clusters, nebulæ, and temporary stars will be found arranged under the heads oftheir respective constellations. 

ANDROMEDA, Map No. 24, 125. Stars: alpha, 126. Gamma, 128. , 126. 36, 128. Temporary star: 1885, 127. Cluster: 457, 128. Variable: R, 128. Nebula: 116, 126. 

AQUARIUS, Map No. 18, 107. Stars: zeta, 106. Tau, 108. Psi, 108. 41, 106. Sigma 2729, 106. Sigma 2745 (12), 106. Sigma 2998, 108. Variables: R, 108. S, 108. T, 106. Nebulæ: 4628 (Rosse's "Saturn"), 108. 4678, 108. 

AQUILA, Map No. 16, 95. Stars: pi, 94. 11, 94. 23, 94. 57, 94. Sigma 2644, 94. Sigma 2544, 94. Cluster: 4440, 94. Variables: eta, 94. R, 94. 

ARGO: Map No. 2, 31; Map No. 7, 55. Stars: Sigma 1097, 33. Sigma 1146 (5), 35. Clusters: 1551, 35. 1564, 35. 1571, 35. 1630, 56. Nebula: 1564, 35. 

ARIES, Map No. 22, 119. Stars: gamma, 118. Epsilon, 120. Lambda, 118. Pi, 118. 14, 118. 30, 118. 41, 118. 52, 120. Sigma 289, 118. 

AURIGA, Map No. 5, 45. Stars: alpha (Capella), 44. Beta (Menkalina), 46. Epsilon, 50. Theta, 48. Lambda, 50. 14, 50. 26, 50. 41, 51. Sigma 616, 48. Temporary star: 1892, 48. Clusters: 996, 51. 1067, 51. 1119, 51. 1166, 51. 1295, 48. 

BOÖTES, Map No. 11, 67. Stars: alpha (Arcturus), 66. Delta, 71. Epsilon (Mirac), 71. Zeta, 70. Iota, 71. Kappa, 71. , 71. Xi, 70. Pi, 70. Sigma 1772, 70. Sigma 1890 (39), 71. Sigma 1909 (44), 71. Sigma 1910 (279), 70. Sigma 1926, 71. 

CAMELOPARDALUS, Map No. 25, 133. Stars: 1, 134. 2, 134. 7, 135. Sigma 385, 134. Sigma 390, 134. Cluster: 940, 135. 

CANES VENATICI, Map No. 26, 137; Map No. 11, 67. Stars: 2, 136. 12 (Cor Caroli), 136. Sigma 1606, 136. Sigma 1768 (25), 72. Cluster: 3936, 72. Nebula: 3572, 136. 

CANIS MAJOR, Map No. 2, 31. Stars: alpha (Sirius), 30. Delta, 33. , 33. Clusters: 1454, 33. 1479, 33. 1512, 33. Variable: gamma, 33. Nebula: 1511, 33. 

CANIS MINOR, Map No. 3, 34. Stars: alpha (Procyon), 36. 14, 36. Sigma 1126 (31 Can. Min. Bode), 36. 

CANCER, Map No. 4, 39. Stars: zeta, 43. Iota, 44. 66, 44. Sigma 1223, 44. Sigma 1291, 44. Sigma 1311, 44. Clusters: Præsepe, 43. 1712, 44. 

CAPRICORNUS, Map No. 13, 83; Map No. 18, 107. Stars: alpha, 84. Beta, 85. Omicron, 85. Pi, 85. Rho, 85. Sigma, 85. Cluster: 4608, 85. 

CASSIOPEIA, Map No. 25, 133. Stars: eta, 132. Iota, 132. Sigma, 132. Psi, 132. Temporary star: 1572 (Tycho's), 134. Cluster: 392, 134. 

CEPHEUS, Map No. 25, 133. 

CETUS, Map No. 20, 112. Stars: alpha, 118. Gamma, 113. Zeta, 111. Eta, 111. 26, 111. 42, 111. Variables: omicron (Mira), 111. R, 113. S, 113. 

COLUMBA, Map No. 2, 31. 

COMA BERENICES, Map No. 6, 53. Stars: 2, 54. 12, 54. 17, 54. 24, 54. 35, 54. 42, 54. Clusters: 2752, 56. 3453, 56. 

CORONA BOREALIS, Map No. 11, 67. Stars: gamma, 72. Zeta, 73. Eta, 72. Nu, 73. Sigma, 73. Sigma 1932, 72. Temporary star: 1866, 73. 

CORVUS, Map No. 8, 58. Star: delta, 57. 

CRATER, Map No. 8, 58. Variable: R, 57. 

CYGNUS, Map No. 17, 99. Stars: beta (Albireo), 103. Delta, 104. Lambda, 105. , 105. Omicron^2, 104. Chi (17), 104. Psi, 104. 49, 104. 52, 104. 61, 105. Temporary star: 1876, 105. Cluster: 4681, 105. Variable: chi, 104. 

DELPHINUS, Map No. 16, 95. Stars: alpha, 96. Beta, 96. Gamma, 94. 

DRACO, Map No. 15, 91; Map No. 26, 137. Stars: gamma, 93. Epsilon, 93. Eta, 93. , 93. Nu, 93. Sigma 1984, 93. Sigma 2054, 93. Sigma 2078 (17), 93. Sigma 2323, 93. Nebulæ: 4373, 93. 4415, 94. 

EQUULEUS, Map No. 18, 107. Stars: beta, 109. Gamma, 109. Sigma 2735, 108. Sigma 2737, 108. Sigma 2742, 108. Sigma 2744, 108. 

ERIDANUS, Map No. 21, 115. Stars: gamma, 114. Omicron^2, 116. 12, 114. Sigma 470 (32), 114. Sigma 516 (39), 114. Sigma 590, 116. Nebula: 826, 116. 

GEMINI, Map No. 4, 39. Stars: alpha (Castor), 38. Beta (Pollux), 40. Gamma, 43. Delta, 41. Epsilon, 43. Zeta, 41. Eta, 42. Kappa, 40. Lambda, 43. , 43. Pi, 40. 15, 43. 38, 43. Cluster: 1360, 42. Variables: zeta, 41. Eta, 42. R, 41. S, 41. T, 41. U, 41. Nebula: 1532, 41. 

HERCULES, Map No. 14, 87; Map No. 15, 91. Stars: alpha, 89. Gamma, 89. Delta, 89. Zeta, 89. Kappa, 89. , 90. Rho, 90. 42, 90. 95, 90. Sigma 2101, 90. Sigma 2104, 90. Sigma 2215, 90. Sigma 2289, 90. Nebulæ: 4230 (M 13), 92. 4234, 92. 

HYDRA, Map No. 3, 34; Map No. 8, 58; Map No. 10, 65. Stars: alpha, 56. Epsilon, 36. Theta, 36. Bu. 339, 56. Sigma 1245, 36. Variable: R, 59. Nebulæ: 2102, 56. 3128, 59. 

LACERTA, Map No. 17, 99. 

LEO, Map No. 6, 53. Stars: gamma, 52. Iota, 52. Tau, 52. 49, 52. 54, 52. 88, 52. 90, 52. Variable: R, 52. Nebula: 1861, 52. 

LEO MINOR, Map No. 26, 137. 

LEPUS, Map No. 1, 21; Map No. 2, 31. Stars: alpha, 30. Beta, 30. Gamma, 30. Iota, 30. 45, 30. Variable: R, 29. 

LIBRA, Map No. 10, 65. Stars: A, 64. Alpha, 64. Beta, 64. Iota, 64. Variable: delta, 64. 

LYNX, Map No. 5, 45. Stars: 4, 51. 5, 51. 12, 51. 14, 51. 19, 51. 38, 52. Sigma 958, 51. Sigma 1009, 51. Sigma 1333, 51. 

LYRA, Map No. 17, 99. Stars: alpha (Vega), 97. Beta, 100. Epsilon, 98. Zeta, 100. 17, 103. Variable: beta, 100. Nebula: 4447 (Ring), 102. 

MONOCEROS, Map No. 1, 21; Map No. 3, 34. Stars: 4, 35. 8, 35. 11, 35. Sigma 921, 35. Sigma 938, 35. Sigma 950, 35. Sigma 1183, 35. Sigma 1190, 35. Clusters: 1424, 35. 1465, 36. 1483, 36. 1611, 36. 1637, 36. Variable: S, 35. 

OPHIUCHUS, Map No. 12, 77; Map No. 14, 87. Stars: lambda, 86. Tau, 86. 36, 79. 39, 79. 67, 86. 70, 86. 73, 86. Sigma 2166, 86. Sigma 2173, 86. Temporary star: 1604, 80. Clusters: 4211, 79. 4256, 88. 4264, 79. 4268, 79. 4269, 79. 4270, 79. 4315, 88. 4346, 79. 4410, 88. Variable: R, 80. 

ORION, Map No. 1, 21. Stars: alpha (Betelgeuse), 27. Beta (Rigel), 20. Delta, 23. Zeta, 23. Eta, 24. Theta (Trapezium), 25. Iota, 27. Lambda, 28. Rho, 28. Sigma, 24. Tau, 28. Psi^2, 29. Sigma 627, 28. Sigma 629, 28. Sigma 652, 28. Sigma 725, 24. Sigma 728 (A 32), 28. Sigma 729, 29. Sigma 747, 27. Sigma 750, 27. Sigma 795 (52), 27. Sigma 816, 29. Omicron Sigma 98 (i), 28. Clusters: 905, 29. 1184, 27. 1361, 29. 1376, 29. Nebulæ: Great Orion Nebula, 25. 1227, 23. 1267, 29. 

PEGASUS, Map No. 19, 110. Stars: beta, 109. Gamma, 109. Epsilon, 109. Eta, 109. 

PERSEUS, Map No. 24, 125. Stars: epsilon, 129. Zeta, 130. Eta, 129. Clusters: 512, 129. 521, 129. Variable: beta (Algol), 130. 

PISCES, Map No. 18, 107; Map No. 20, 112; Map No. 22, 119. Stars: alpha, 117. Zeta, 117. Psi, 117. 55, 117. 65, 117. 66, 117. 77, 117. Variable: R, 118. 

SAGITTA, Map No. 16, 95. Stars: epsilon, 94. Zeta, 94. Theta, 94. Nebula: 4572, 94. 

SAGITTARIUS, Map No. 12, 77; Map No. 13, 83. Stars:, 80. 54, 84. Clusters: M 25, 81. 4355, 81. 4361 (M 8), 81. 4397 (M 24), 81. 4424, 84. Variables: R, 84. T, 84. U, 82. V, 82. 

SCORPIO, Map No. 12, 77. Stars: alpha (Antares), 75. Beta, 76. Nu, 76. Xi, 76. Sigma, 76. Temporary star: 1860, 78. Clusters: 4173, 78. 4183, 78. 

SCUTUM SOBIESKII, Map No. 12, 77; Map No. 13, 83. Stars: Sigma 2306, 82. Sigma 2325, 82. Clusters: 4400, 82. 4426, 82. 4437, 82. Variable: R, 82. Nebula: 4441, 82. 

SERPENS, Map No. 12, 77; Map No. 14, 87. Stars: alpha, 86. Beta, 86. Delta, 86. Theta, 88. Nu, 86. Variable: R, 86. 

TAURUS, Map No. 23, 121. Stars: alpha (Aldebaran), 123. Eta (Alcyone), 120. Theta, 123. Kappa, 123. Sigma, 124. Tau, 124. Phi, 123. Chi, 123. 30, 122. Sigma 412 (7), 120. Sigma 430, 122. Sigma 674, 124. Sigma 716, 124. Clusters: Hyades, 120. Pleiades, 120. 1030, 124. Variable: lambda, 122. Nebulæ: in Pleiades, 120. 1157 (Crab Net), 124. 

TRIANGULUM, Map No. 24, 125. Star: 6, 129. Nebula: 352, 129. 

URSA MAJOR, Map No. 26, 137. Stars: zeta (Mizar), 135. Iota, 135. Nu, 135. Xi, 135. Sigma^2, 135. 23, 135. 57, 135. 65, 135. Nebulæ: 1949, 136. 1950, 136. 2343, 136. 

URSA MINOR, Map No. 26, 137. Stars: alpha (Pole Star), 138. Pi, 138. 

VIRGO, Map No. 9, 61. Stars: alpha (Spica), 59. Gamma, 59. Theta, 60. 84, 62. Sigma 1669, 59. Sigma 1846, 62. Variables: R, 63. S, 63. U, 63. Nebulæ: Field of the, 62. 2806, 63. 2961, 63. 3105, 63. 

VULPECULA, Map No. 17, 99. Star: Sigma 2695, 106. Temporary star: 1670, 106. Nebula: 4532 (Dumb Bell), 106. 

THE MOON, most interesting of telescopic objects, 156; telescopic views of moon reversed, 157. Craters, ring mountains, and ringed plains: Agatharchides, 179. Agrippa, 168. Albategnius, 171. Alhazen, 160. Aliacensis, 171. Alphonsus, 176. Archimedes, 175. Ariadæus, 168. Aristarchus, 174. Aristillus, 167. Aristoteles, 162. Arzachel, 176. Atlas, 160. Autolycus, 167. Bailly, 178. Ball, 176. Barrow, 162. Beer, 175. Berzelius, 160. Billy, 179. Bullialdus, 180. Burckhardt, 157. Capuanus, 179. Cassini, 167. Catharina, 170, Cichus, 179. Clavius, 178. Cleomenes, 159. Condorcet, 160. Copernicus, 175. Cyrillus, 170. Délisle, 174 Endymion, 160. Eratosthenes, 175. Eudoxus, 162. Euler, 174. Firmicus, 160. Fracastorius, 169, 179. Furnerius, 161. Gassendi, 179. Gauss, 159. Geminus, 160. Goclenius, 169. Godin, 168. Grimaldi, 179. Guttemberg, 169. Hainzel, 179. Hansen, 160. Helicon, 174. Hell, 176. Hercules, 160. Herodotus, 174. Herschel, Caroline, 174. Hipparchus, 171. Humboldt, 161. Hyginus, 168. Julius Cæsar, 168. Kepler, 176. Lambert, 174. Landsberg, 180. Langrenus, 160, 168. Letronne, 179. Leverrier, 174. Lexell, 176. Lichtenberg, 174. Linné, 165. Longomontanus, 178. Macrobius, 159. Maginus, 178. Manilius, 166. Maurolycus, 172. Menelaus, 166. Mercator, 179. Mersenius, 179. Messala, 160. Messier, 169. Newton, 178. Petavius, 160, 168. Picard, 157. Piccolomini, 171. Pico, 172. Plato, 172. Plinius, 166. Posidonius, 163, 164. Proclus, 158. Ptolemæus, 176. Purbach, 176. Sacrobosco, 171. Schickard, 178. Schiller, 178. Silberschlag, 168. Stöfler, 171. Sulpicius Gallus, 166. Theætetus, 167. Thebit, 176. Theophilus, 170. Timocharis, 174. Tobias Mayer, 176. Tralles, 159. Triesnecker, 168. Tycho, 177, 178. Vendelinus, 160, 168. Vieta, 179. Vitello, 179. Walter, 171. Wargentin, 179. Werner, 171. Wilhelm I, 178. _Maria_, or "Seas": _Lacus Somniorum_, 163. _Mare Crisium_, 157, 159, 160. _Mare Fecunditatis_, 160, 168. _Mare Frigoris_, 162, 172. _Mare Humboldtianum_, 160. _Mare Humorum_, 176, 179. _Mare Imbrium_, 163, 172, 174. _Mare Nectaris_, 168. _Mare Nubium_, 176. _Mare Serenitatis_, 163, 164, 165. _Mare Tranquilitatis_, 168. _Mare Vaporum_, 166, 167. _Oceanus Procellarum_, 172, 176, 179. _Palus Nebularum_, 167. _Palus Putredinis_, 167. _Palus Somnii_, 159. _Sinus Æstuum_, 172. _Sinus Iridum_, 172, 173. Other formations: Alps Mountains, 163. Apennine Mountains, 163, 167, 175. Cape Agarum, 158. Cape Heraclides, 173. Cape Laplace, 173. Carpathian Mountains, 176. Caucasus Mountains, 163. Cordilleras Mountains, 180. D'Alembert Mountains, 180. Dörfel Mountains, 180. Hæmus Mountains, 165. Harbinger Mountains, 174. Leibnitz Mountains, 180. "Lunar Railroad, " 176. Mt. Argæus, 165, 167. Mt. Hadley, 167. Mt. Huygens, 175. Pyrenees Mountains, 169. Taurus Mountains, 164. 

THE PLANETS: Are there planets among the stars? 183. Mars, two views of, 17. Best advertised of planets, 151. Favorable oppositions of, 152. Seen with 5-inch telescope, 152. Polar caps of, 152. Color of, 152. Dark markings on, 152. "canals, " 153. Earthlike condition of, 153. Mercury, phases of, 155. Peculiar rotation of, 155. Markings on, 155. Probably not habitable, 155. Jupiter, easiest planet for amateurs, 141. Seen with 5-inch glass, 141. Satellites, swift motions of, 142. Velocity of planet's equator, 142. How to see all sides of, 142, 143. Watching rotation of, 143. Eclipses and transits of satellites, 144, 147. Belts and clouds of, 145. Different rates of rotation, 145. Names and numbers of satellites, 146. Saturn, next to Jupiter in attractiveness, 147. Seen with 5-inch glass, 148. Its moons and their orbits, 148, 149. Polar view of system, 149. Roche's limit, 149, 150. Origin of the rings, 150. Pickering's ninth satellite, 151. The satellites as telescopic objects, 151. Venus, her wonderful brilliance, 153. Her atmosphere seen, 153. Lowell's observations, 153. Schiaparelli's observations, 154. Her peculiar rotation, 154. How to see, in daytime, 155. Neptune and Uranus, 155. 

THE SUN, 181. Shade glasses for telescopes in viewing, 181. Solar prism, 181. Helioscope, 181. Periodicity of spots, 181. To see, by projection, 182. Spectroscope for solar observation, 182. 

THE TELESCOPE: refractors and reflectors, 2, 8. Eyepieces, 6, 9, 10. Aberration (chromatic), 6; (spherical), 6, 17. Achromatic telescopes, how made, 7. Object glass, 8. Magnifying power, 11. Mountings, 12. Rules for testing, 13. Image of star in, 14. Image in and out of focus, 14, 15, 17. Astigmatism, 16. 

THE END

[Illustration]

 1692 S. _Pleasures of the Telescope_ _GARRETT P. SERVISS_

 This book says to the amateur, in effect:--"What if you have not all advantages of clockwork and observatory equipment. You may know something of the witchery of the heavens even with a little telescope of three to five inches aperture!" "Pleasures of the Telescope" is popular in style rather than technical. For setting forth "the chief attractions of the starry heavens, " a complete set of star-maps is included, showing "all the stars visible to the naked eye in the regions of sky represented, and in addition some stars that can only be seen with optical aid. " In six chapters these twenty-six maps are described so plainly that the amateur can readily find all the interesting star-groups, clusters, and nebulæ, and also the colored or double stars. In the three concluding chapters the moon and planets receive special consideration. In the opening chapter the amateur is told how to select and test a glass. 

 _Booklovers Bulletin. _

Transcriber's Note

Minor errors and inconsistencies in punctuation and hyphenation havebeen silently corrected. 

Some illustrations have been relocated a short distance within the text. 

Original page numbers have been retained in the index. 

Greek letters, used to identify stars, are replaced with the full nameof the Greek letter, e. G. Alpha. Upper case Greek letters are shown bycapitalising the initial letter, e. G. Sigma 1126

A caret (^) is used to represent superscripts, e. G. Nu^1 and nu^2

The following minor corrections have also been made:

p3: "wil" has been corrected to "will". 

p28: Sigma 629 is not shown on Map No. 1. The location of _m_ Orionisis marked as Sigma 696. This inconsistency has not been corrected. 

p54: "for colors" has been corrected to "four colors". 

p68: "1, 065, 790, 250, 000, 000" has been corrected to"1, 065, 702, 500, 000, 000". 

p163-164: "magnical" has been corrected to "magical". 

p179: A repeated "and" has been removed.