tneusejgofMembers only* OFFICES. 1323WALNVT Street PHILADELPHIA THE LIBRARY OF THE UNIVERSITY OF CALIFORNIA PRESENTED BY PROF. CHARLES A. KOFOID AND MRS. PRUDENCE W. KOFOID PLEASUEES OF THE TELESCOPE PLEASUKES 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 1 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 quake Big with the birth of stars, and when He spake A million worlds leapt into radiant light. 1 '' 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 specially for the use of the amateur and dis- tributed through the body of the work, thus facilitating consultation, it is believed that this book makes a step in advance of its predecessors. The maps show all of the stars visible to the naked eye in the regions of sky repre- sented, and, in addition, some stars that can only be seen with optical aid. The latter have been placed in the maps as guide posts in the telescopic field to assist those who are searching for faint and inconspicuous objects referred to in the text. As the book was not written for those who possess the equipment of an observatory, with telescopes driven by clockwork and provided with graduated circles, right ascensions and declinations are not given. All of the telescopic phenomena described are, however, repre- sented in the maps. Star clusters are indicated by a con- ventional symbol, and nebulae by a little white circle; while a small cross serves to mark the places where nota- ble new stars have appeared. The relative magnitudes of the stars are approximately shown by the dimensions of their symbols in the maps, the smaller stars being repre- sented 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 posi- tion change so rapidly that any statement concerning them remains valid only for a few years at the most. There is also much confusion among the measurements vi PLEASURES OF THE TELESCOPE announced by different authorities. In general, the most recent measurements obtainable in 1900 are given in the text, but the observer who wishes to study close and rapid binaries will do well to revise his information about them as frequently as possible. An excellent list of double stars kept up to date, will be found in the annual Com- panion to the Observatory, published in London. In the lunar charts the plan of inserting the names of the principal formations has been preferred to that usually followed, of indicating them only by numbers, accompanied by a key list. Even in the most detailed charts of the moon only a part of what is visible with telescopes can be shown, and the representation, at best, must be merely approximate. It is simply a question of what to include and what to omit; and in the present case the probable needs of the amateur observer have governed the selec- tion readiness and convenience of reference being the chief aim. It should, perhaps, be said here that the various chap- ters composing this book like those of " Astronomy with an Opera-glass " were, in their original form, with the single exception of Chapter IX, published in Appletons' Popular Science Monthly. The author, it is needless to say, was much gratified by the expressed wish of many readers that these scattered papers should be revised and collected in a more permanent form. As bearing upon the general subject of the book, a chapter has been added, at the end, treating on the question of the existence of planets among the stars. This also first appeared in the periodical above mentioned. In conclusion, the author wishes for his readers as great a pleasure in the use of the telescope as he himself has enjoyed. GPS 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 and refractors How a telescope is made achromatic The way to test a 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 their neighbors Auriga, the Lynx, Hydra, Sextans, and Coma Berenices. CHAPTER IV VIRGO AND HER NEIGHBORS 57 Crater and Corvus, Hydra, Virgo, the "Field of the Nebulae," Libra, Bootes, and the great Arcturus, Canes Venatici, and Corona Borealis. CHAPTER V IN SUMMER STAR-LANDS 75 Scorpio and its red-green gem. Ophiuchus, Sagittarius, Scutum Sobieskii, Capricornus, Serpens, Hercules, Draco, Aquila, and Delphinus. CHAPTER VI FROM LYRA TO ERIDANUS v ... . .97 Lyra and its brilliant Vega, Cygnus, Vulpecula, Aquarius, Equuleus, Pegasus, Cetus, and Eridanus. vii viii PLEASURES OF THE TELESCOPE CHAPTER VII PAGE PISCES, ARIES, TAURUS, AND THE NORTHERN MARS .... 117 The first double star ever discovered, the Pleiades and their photo- graphic 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 ringed planet Saturn's moons and Roche's limit Mars and its white polar caps and so-called seas and continents Venus and her atmosphere The peculiar rota- tions of Venus and Mercury. CHAPTER IX THE MOUNTAINS AND PLAINS OF THE MOON AND THE SPECTACLES OF THE SUN 156 Peculiarities of the lunar landscapes The sVcalled seas, the craters, the ring mountains, the inclosed plains, the mountain ranges, Tycho's mysterious streaks, and other lunar features described 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 do not show planets circling around distant suns Reasons for thinking that such planets may exist The bearing of stellar evolution on the ques- tion. PLEASURES OP THE TELESCOPE CHAPTER I THE SELECTION AND TESTING OF A GLASS "O telescope, instrument of much knowledge, more precious than any scep- ter! 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 and use of a good telescope of three, four, five, or six inches aperture were generally known, I am certain that no instrument of science would be more com- monly found in the homes of intelligent people. The writer, when a boy, discovered unexpected powers in a pocket telescope not more than fourteen inches long when extended, and magnifying ten or twelve times. It became his dream, which was afterward realized, to possess a more powerful telescope, a real astronomical glass, with which he could see the beauties of the double stars, the craters of the moon, the spots on the sun, the belts and satellites of Jupiter, the rings .of Saturn, the extraor- dinary shapes of the nebula, the crowds of stars in the Milky Way, and the great stellar clusters. And now he would do what he can to persuade others, who perhaps are not aware how near at hand it lies, to look for them- selves into the wonder-world of the astronomers. There is only one way in which you can be sure of getting a good telescope. First, decide how large a glass you are to have, then go to a maker of established reputa- 2 PLEASURES OF THE TELESCOPE tion, fix upon the price you are willing to pay remem- bering that good work is never cheap and finally see that the instrument furnished to you answers the proper tests for a telescope of its size. There are telescopes and telescopes. Occasionally a rare combination of perfect homogeneity in the material, complete harmony between the two kinds of glass of which the objective is composed, and lens surfaces whose curves are absolutely right, pro- duces a telescope whose owner would part with his last dollar sooner than with it. Such treasures of the lens- maker's art can not, perhaps, be commanded at will, yet, they are turned out with increasing frequency, and the best artists are generally able, at all times, to approxi- mate so closely to perfection that any shortcoming may be disregarded. In what is said above I refer, of course, to the refract- ing telescope, which is the form of instrument that I should recommend to all amateurs in preference to the reflector. But, before proceeding further, it may be well to recall briefly the principal points of difference between these two kinds of telescopes. The purpose of a telescope of either description is, first, to form an image of the object looked at by concentrating at a focus the rays of light proceeding from that object. The refractor achieves this by means of a carefully shaped lens, called the object glass, or objective. The reflector, on the other hand, forms the image at the focus of a concave mirror. A very pretty little experiment, which illustrates these two methods of forming an optical image, and, by way of corollary, exemplifies the essential difference between re- fracting and reflecting telescopes, may be performed by any one who possesses a reading glass and a magnifying hand mirror. In a room that is not too brightly illumi- nated pin a sheet of white paper on the wall opposite to a THE SELECTION AND TESTING OF A GLASS 3 window that, by preference, should face the north, or away from the position of the sun. Taking first the read- ing glass, hold it between the window and the wall paral- IMAGE AT THE Focus OF A LENS. lei to the sheet of paper, and a foot or more distant from the latter. By moving it to and fro a little you wil be able to find a distance, corresponding to the focal length of the lens, at which a picture of the window is formed on the paper. This picture, or image, will be upside down, be- cause the rays of light cross at the focus. By moving the glass a little closer to the wall you will cause the picture 4 PLEASURES OF THE TELESCOPE of the window to become indistinct, while a beautiful im- age of the houses, trees, or other objects of the outdoor world beyond, will be formed upon the paper. We thus learn that the distance of the image 'from the 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 the object glass of a refracting telescope. IMAGE AT THE Focus OF A CONCAVE MIRROR. Take next your magnifying or concave mirror, and detaching the sheet of paper from the wall, hold it nearly in front of the mirror between the latter and the window. THE SELECTION AND TESTING OF A GLASS 5 When you have adjusted the distance to the focal length of the mirror, you will see an image of the window pro- jected upon the paper, and by varying the distance, as before, you will be able to produce, at will, pictures of nearer or more remote objects. It is in this way that images are formed at the focus of the mirror of a reflect- ing telescope. Now, you w r ill have observed that the chief apparent difference between these two methods of forming an im- age of distant objects is that in the first case the rays of light, passing through the transparent lens, are brought to a focus on the side opposite to that where the real object is, while in the second case the rays, being reflected from the brilliant surface of the opaque mirror, come to a focus on the same side as that on which the object itself is. From this follows the most striking difference in the method of using refracting and reflecting tele- scopes. In the refractor the observer looks toward the object; in the reflector he looks away from it. Sir Wil- liam Herschel made his great discoveries with his back to the sky. He used reflecting telescopes. This principle, again, can be readily illustrated by means of our simple experiment with a reading glass and a magnifying mirror. Hold the reading glass between the eye and a distant object with one hand, and with 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 carefully until they are at a distance apart equal to the sum of the focal lengths of the lenses, and you will see a magnified image of the distant object. In other words, you have constructed a simple refracting telescope. Then take the magnifying mirror, and, turning your back to the object to be looked at, use the small lens as before that is to say, hold it- between your eye and the mirror, so that its 6 PLEASURES OF THE TELESCOPE distance from the latter is equal to the sum of the focal lengths of the mirror and the lens, and you will see again a magnified image of the distant object. This time it is a reflecting telescope that you hold in your hands. The magnification of the image reminds us of the second purpose which is subserved by a telescope. A telescope, whether* refracting or reflecting, consists of two essential parts, the first being a lens, or a mirror, to form an image, and the second a microscope, called an eyepiece, to magnify the image. The same eyepieces will serve for either the reflector or the refractor. But in order that the magnification may be effective, and serve to reveal what could not be seen without it, the image itself must be as nearly perfect as possible; this requires that every ray of light that forms the image shall be brought to a point in the image precisely corresponding to that from which it emanates in the real object. In reflectors this is effected by giving a parabolic form to the concave surface of the mirror. In refractors there is a twofold difficulty to be overcome. In the first place, a lens with spherical surfaces does not bend all the rays that pass through it to a focus at precisely the same dis- tance. The rays that pass near the outer edge of the lens have a shorter focus than that of the rays which pass near the center of the lens; this is called spherical aberra- tion. A similar phenomenon occurs with a concave mir- ror whose surface is spherical. In that case, as we have seen, the difficulty is overcome by giving the mirror a parabolic instead of a spherical form. In an analogous way the spherical aberration of a lens can be corrected by altering its curves, but the second difficulty that arises with a lens is not so easily disposed of: this is what is called chromatic aberration. It is due to the fact that the rays belonging to different parts of the spectrum have TEE SELECTION AND TESTING OF A GLASS 7 different degrees of refrangibility, or, in other words, that they come to a focus at different distances from the lens; and this is independent of the form of the lens. The blue rays come to a focus first, then the yellow, and finally the red. It results from this scattering of the spectral rays along the axis of the lens that there is no single and exact focus where all meet, and that the image of a star, for instance, formed by an ordinary lens, even if the spherical aberration has been corrected, appears blurred and dis- colored. There is no such difficulty with a mirror, be- cause there is in that case no refraction of the light, and consequently no splitting up of the elements of the spec- trum. In order to get around the obstacle formed by chro- matic aberration it is necessary to make the object glass of a refractor consist of two lenses, each composed of a different kind of glass. One of the most interesting facts in the history of the telescope is that Sir Isaac Newton could see no hope that chromatic aberration would be overcome, and accordingly turned his attention to the improvement of the reflecting telescope and devised a form of that instrument which still goes under his name. And even after Chester More Hall in 1729, and John Dol- lond in 1757, had shown that chromatic aberration could be nearly eliminated by the combination of a flint-glass lens with one of crown glass, William Herschel, who began his observations in 1774, devoted his skill entirely to the making of reflectors, seeing no prospect of much advance in the power of refractors. A refracting telescope which has been freed from the effects of chromatic aberration is called achromatic. The principle upon which its construction depends is that by combining lenses of different dispersive power the separa- tion of the spectral colors in the image can be corrected 8 PLEASURES OF THE TELESCOPE ACHROMATIC OBJECT GLASS. a, crown glass ; 6, fliat glass. while the convergence of the rays of light toward a focus is not destroyed. Flint glass effects a greater dispersion than crown glass nearly in the ratio of three to two. The chromatic combination consists of a convex lens of crown backed by a con- cave, or plano-concave, lens of flint. When these two lenses are made of focal lengths which are directly proportional to their dis- persions, they give a prac- tically colorless image at their common focus. The skill of the telescope-maker and the excellence of his work depend upon the selection of the glasses to be combined and his manipulation of the curves of the lenses. Now, the reader may ask, " Since reflectors require no correction for color dispersion, while that correction is only approximately effected by the combination of two kinds of lenses and two kinds of glass in a refractor, why is not the reflector preferable to the refractor? " The answer is, that the refractor gives more light and better definition. It is superior in the first respect be- cause a lens transmits more light than a mirror reflects. Professor Young has remarked that about eighty-two per cent of the light reaches the eye in a good refractor, while " in a Newtonian reflector, in average condition, the per- centage seldom exceeds fifty per cent, and more frequently is lower than higher." The superiority of the refractor in regard to definition arises from the fact that any dis- tortion at the surface of a mirror affects the direction of a ray of light three times as much as the same distortion THE SELECTION AND TESTING OF A GLASS 9 would do at the surface of a lens. And this applies equally both to permanent errors of curvature and to tem- porary distortions produced by strains and by inequality of temperature. The perfect achromatism of a reflector is, of course, a great advantage, but the chromatic aber- ration of refractors is now so well corrected that their inferiority in that respect may be disregarded. It must be admitted that reflectors are cheaper and easier to make, but, on the other hand, they require more care, and their mirrors frequently need resilvering, while an 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 respec- tive properties of object glasses and mirrors, but a word should be added concerning eyepieces. Without a good eyepiece the best telescope will not perform well. The simplest of all eyepieces is a single double-convex lens. With such a lens the magnifying power of the telescope is measured by the ratio of the focal length of the objec- tive to that of the eye lens. Suppose the first is sixty inches and the latter half an inch; then the magnifying power will be a hundred and twenty diameters i. e., the disk of a planet, for instance, will be enlarged a hundred and twenty times along each diameter, and its area will be enlarged the square of a hundred and twenty, or four- teen thousand four hundred times. But in reckoning magnifying power, diameter, not area, is always consid- ered. For practical use an eyepiece composed of an ordi- nary single lens is seldom advantageous, because good definition can only be obtained in the center of the field. Lenses made according to special formula?, however, and called solid eyepieces, give excellent results, and for high powers are often to be preferred to any other. The eye- pieces usually furnished with telescopes are, in their 10 PLEASURES OF THE TELESCOPE essential principles, compound microscopes, and they are of two descriptions, " positive " and " negative." The for- mer generally goes under the name of its inventor, Hams- den, and the latter is name'd 'after the great Dutch astron- omer, Huygens. The Huygens eyepiece consists of two NEGATIVE EYEPIECE. POSITIVE EYEPIECE. plano-convex lenses whose focal lengths are in the ratio of three to one. The smaller lens is placed next to the eye. Both lenses have their convex surfaces toward the object glass, and their distance apart is equal to half the sum of their focal lengths. In this kind of eyepiece the image is formed between the two lenses, and if the work is properly done such an eyepiece is achromatic. It ,is therefore generally preferred for mere seeing purposes. In the Ramsden eyepiece two plano-convex lenses are also used, but they are of equal focal length, are placed at a distance apart equal to two thirds of the focal length of either, and have their convex sides facing one another. With such an eyepiece the image viewed is beyond the farther or field lens instead of between the two lenses, and as this fact renders it easier to adjust wires or lines for measuring purposes in the focus of the eyepiece, the Ramsden construction is used when a micrometer is to be employed. In order to ascertain the magnifying power which an eyepiece gives when applied to a telescope it is necessary to know the equivalent, or combined, focal length of the two lenses. Two simple rules, easily re- membered, supply the means of ascertaining this. The equivalent focal length of a negative or Huygens eyepiece THE SELECTION AND TESTING OF A GLASS H is equal to half the focal length of the larger or field lens. The equivalent focal length of a positive or Ramsden eye- piece is equal to three fourths of the focal length of either of the lenses. Having ascertained the equivalent focal length of the eyepiece, it is only necessary to divide it into the focal length of the object glass (or mirror) in order to know the magnifying power of your telescope when that particular eyepiece is in use. A first-class object glass (or mirror) will bear a mag- nifying power of one hundred to the inch of aperture when the air is in good condition that is, if you are look- ing at stars. If you are viewing the moon, or a planet, better results will always be obtained with lower powers say fifty to the inch at the most. And under ordinary atmospheric conditions a power of from fifty to seventy- five to the inch is far better for stars than a higher power. With a five-inch telescope that would mean from two hun- dred and fifty to three hundred and seventy-five diame- ters, and such powers should only be applied for the sake of separating very close double stars. As a general rule, the lowest power that will distinctly show what you de- sire to see gives the best results. The experienced ob- server never uses as high powers as the beginner does. The number of eyepieces purchased with a telescope should never be less than three a very low power say ten to the inch; a very high 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 can afford it, get a full battery of eyepieces six or eight, or a dozen for experience shows that different objects require differ- ent powers in order to be best seen, and, moreover, a slight change of power is frequently a great relief to the eye. There is one other thing of great importance to be considered in purchasing a telescope the mounting. If 12 PLEASURES OF THE TELESCOPE your glass is not well mounted on a steady and easily managed stand, you might better have spent your money for something more useful. I have endured hours of tor- ment while trying to see stars through a telescope that was shivering in the wind and dancing to every motion of the bystanders, to say nothing of the wriggling contor- tions caused by the application of my own fingers to the focusing screw. The best of all stands is a solid iron pillar firmly fastened into a brick or stone pier, sunk at least four feet in the ground, and surmounted by a well- made equatorial bearing whose polar axis has been care- fully placed in the meridian. It can be readily protected 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 out and placed on its bearing only when ob- servations are to be made. With such a mounting you can laugh at the observatories with their cumbersome domes, for the best of all observatories is the open air. But if you dislike the labor'of carrying and adjusting the tube every time it is used, and are both fond of and able to procure luxuries, then, after all, perhaps, you had better have the observatory, dome, draughts and all. The next best thing in the way of a mounting is a port- able tripod stand. This may be furnished either with an equatorial bearing for the telescope, or an altazimuth arrangement which permits both up-and-down and hori- zontal motions. The latter is cheaper than the equatorial and proportionately inferior in usefulness and conven- ience. The essential principle of the equatorial bearing is motion about two axes placed at right angles to one another. When the polar axis is in the meridian, and in- clined at an angle equal to the latitude of the place, the telescope can be moved about the two axes in such a way as to point to any quarter of the sky, and the motion of a THE SELECTION AND TESTING OF A GLASS 13 star, arising from the earth's rotation, can be followed hour after hour without disturbing the instrument. When thus mounted, the telescope may be driven by clock- work, or by hand with the aid of a screw geared to a handle carrying a universal joint. And now for testing the telescope. It has already been remarked that the excellence of a telescope depends upon the perfection of the image formed at the focus of the objective. In what follows I have only a refractor in mind, although the same principles would apply to a re- flector. With a little practice anybody who has a correct eye can form a fair judgment of the excellence of a tele- scopic image. Suppose we have our telescope steadily mounted out of doors (if you value your peace of mind you will not try to use a telescope pointed out of a window, especially in winter), and suppose we begin our observa- tions with the pole 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. If the air is not reasonably steady we had better postpone our experiment to another night, because we shall find that the star as seen in the telescope flickers and " boils," and behaves in so extraordinary a fashion that there is no more defini- tion in the image than there is steadiness in a bluebottle buzzing on a window pane. But if the night is a fine one the star image will be quiescent, and then we may note the following particulars: The real image is a minute bright disk, about one second of arc in diameter if we are using a four-and-a-half or five-inch telescope, and surrounded by one very thin ring of light, and the fragments, so to speak, of one or possibly two similar rings a little farther from the disk, and visible, perhaps, only by glimpses. These " diffraction rings " arise from the undulatory nature of light, and their distance apart as well as the diameter of 14: PLEASURES OF THE TELESCOPE the central disk depend upon the 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 will be perfectly round, slightly softer at the edge, but otherwise equally bright throughout; and the ring or rings surrounding it will be exactly concentric, and not brighter on one side than on another. Even if our tele- scope were only two inches or two inches and a half in aperture we should at once notice a little bluish star, the mere ghost of a star in a small telescope, hovering near the polar star. It is the celebrated " companion," but we shall see it again wnen we have more time to study it. 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 slightly outside the focus, or away from the object glass. Very beautiful phenomena im- mediately begin to make their appearance. A slight motion outward causes the little disk to expand perceptibly, and just as this expan- sion commences, a bright-red point appears at the precise center of the disk. But, the outward motion continuing, this red center disappears, and is replaced by a blue center, which gradually expands into a sort of flare over the middle of the disk. The disk itself has in the mean time enlarged into a series of concentric bright rings, graduated in luminosity with beautiful precision from center toward circumference. The outermost ring is considerably brighter, however, than it would be if the same gradation applied to it as applies to the inner rings, and it is surrounded, moreover, on its outer edge by a slight flare which tends to increase its apparent width. Next let us return to the focus and then move the eyepiece gradually inside the focal point or plane. Once more the star disk expands into a series of circles, THE SELECTION AND TESTING OF A GLASS 15 and, if we except the color phenomena noticed outside the focus, these circles are precisely like those seen before in arrangement, in size, and in brightness. If they were not the same, we should pronounce the telescope to be im- perfect. There is one other difference, however, besides the absence of the blue central flare, and that is a faint reddish edging around the outer ring when the expansion inside the focus is not carried very far. Upon continuing to move the eyepiece inside or outside the focus we ob- serve that the system of rings becomes larger, while the rings themselves rapidly increase in number, becoming at the same time individually thinner and fainter. By studying the appearance of the star disk when in focus and of the rings when out of focus on either side, an experienced eye can readily detect any fault that a tele- scope may have. The amateur, of course, can only learn to do this by considerable practice. Any glaring and seri- ous fault, however, will easily make itself manifest. Sup- pose, for example, we observe that the image of a star instead of being perfectly round is oblong, and that a simi- lar defect appears in the form of the rings when the eye- piece is put out of focus. We know at once that some- thing is wrong; but the trouble may lie either in the ob- ject glass, in the eyepiece, in the eye of the observer him- self, or in the adjustment of the lenses in the tube. A careful examination of the image and the out-of-focus circles will enable us to determine with which of these sources of error we have to deal. If the star image when in focus has a sort of wing on one side, and if the rings out of focus expand eccentrically, appearing wider and larger on one side than on the other, being at the same time brightest on the least expanded side, then the object glass is probably not at right angles to the axis of the tube and requires readjustment. That part of the object 16 PLEASURES OF THE TELESCOPE glass on the side where the rings appear most expanded and faintest needs to be pushed slightly inward. This can be effected by means of counterscrews placed for that purpose in or around the cell. But if, after we have got the object glass properly squared to the axis of the tube or the line of sight, the image and the ring system in and out of focus still appear oblong, the fault 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 is at fault. We may be certain of this if we find, on turning the head so as to look into the telescope with the eye in different positions, that the oblong image turns with the head of the observer, keeping its major axis con- tinually in the same relative position with respect to the eye. The remedy then is to consult an oculist and get a pair of cylindrical eyeglasses. If the oblong image does not turn round with the eye, but does turn when the eye- piece is twisted round, then the astigmatism is in the lat- ter. If, finally, it does not follow either the eye or the eyepiece, it is the objective that is at fault. But instead of being oblong, the image and the rings may be misshapen in some other way. If they are three- cornered, it is probable that the object glass is subjected to undue pressure in its cell. This, if the telescope has been brought out on a cool night from a warm room, may arise from the unequal contraction of the metal work and the glass as they cool off. In fact, no good star image can be got while a telescope is assuming the temperature of the surrounding atmosphere. Even the air inclosed in the tube is capable of making much trouble until its tem- perature has sunk to the level of that outside. Half an hour at least is 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 for such adjustment in THE SELECTION AND TESTING OF A GLASS 17 cold weather. Any irregularity in the shape of the rings which persists after the lenses have been accurately ad- justed and the telescope has properly cooled may be as- cribed to imperfections, such as veins or spots of unequal density in the glass forming the objective. The spherical aberration of an object glass may be under- corrected or overcorrected. In the former case the central rings inside the focus will appear faint and the outer ones unduly strong, while outside the focus the central rings will be too bright and the outer ones too feeble. But if the aberration is overcorrected the central rings will be overbright inside the focus and abnormally faint outside the focus. Assuming that we have a telescope in which no ob- vious fault is discernible, the next thing is to test its pow- 123 THE OuT-OF-Focus RINGS. 1, Correct figure ; 2 and 3, spher- ical aberration. Two VIEWS OF MARS IN The smaller with a three-and-three-eighths-inch telescope ; the larger with a nine-inch. ers in actual work. In what is to follow I shall endeavor to describe some of the principal objects in the heavens from which the amateur observer may expect to derive pleasure and instruction, and which may at the same time 18 PLEASURES OF THE TELESCOPE serve as tests of the excellence of his telescope. No one should be deterred or discouraged in the study of celes- tial objects by the apparent insignificance of his means of observation. The accompanying pictures of the planet Mars may serve as an indication of the fact that a small telescope is frequently capable of doing work that ap- pears by no means contemptible when placed side by side with that of the greater instruments 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 mounted telescopes of five, four, and three inches aperture, respectively. A fine midwinter evening has come along, the air is clear, cool, and steady, and the heavens, of that almost invisible' violet which is reserved for the lovers of celestial scenery, are spangled with stars that hardly twinkle. We need not disturb our minds about a few thin clouds here and there floating lazily in the high air; they announce a change 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 in- stinctively return to the south, and are lifted to behold Orion in his glory, now near the meridian and midway to the zenith, with Taurus shaking the glittering Pleiades before him, and Canis Major with the flaming Dog Star following at his heels. Not only is Orion the most brilliant of all constella- tions to the casual star-gazer, but it contains the richest mines that the delver for telescopic treasures can any- where discover. We could not have made a better begin- ning, for here within a space of a few square degrees we have a wonderful variety of double stars and multiple 19 20 PLEASURES OF THE TELESCOPE stars, so close and delicate as to test the powers of the best telescopes, besides a profusion of star-clusters and nebulae, including one of the supreme marvels of space, the Great Nebula in the Sword. Our star map No. 1 will serve as a guide to the objects which we are about to inspect. Let us begin operations with our smallest telescope, the three-inch. I may re- mark here that, just as the lowest magnifying power that will clearly reveal the object looked for gives ordinarily better results than a higher power, so the smallest tele- scope that is competent to show what one wishes to see is likely to yield more satisfaction, as far as that particu- lar object is concerned, than a larger glass. The larger the object glass and the higher the power, the greater are the atmospheric difficulties. A small telescope will per- form very well on a night when a large one is helpless. Turn the glass upon /3 (Rigel), the white first-magni- tude star in Orion'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 rings in and out of focus, and if you are satisfied with the performance, try for the companion. A good three-inch is certain to show it, except in a bad state of the atmosphere, and even then an expert can see it, at least by glimpses. The com- panion is of the ninth magnitude, some say the eighth, and the distance is about 9.5", angle of position (hereafter designated by p.) 199.* Its color is blue, in decided con- * The angle of position measures the inclination to the meridian of a line drawn between the principal star and its companion ; in other words, it shows in what direction from the primary we must look for the companion. It is reckoned from up to 360, beginning at the north point and passing around by east through south and west to north again. Thus, if the angle of position is or 360, the companion is on the north side of the primary; if the angle is 90, the companion is to the east; if 180, to the south; if 270, to the west, and so for intermediate angles. It must be remembered, however, that in the field of the telescope the top is south and the bottom north, unless a prism is used, when MAP No. i. 22 PLEASURES OF THE TELESCOPE trast with the white light of its great primary. Sir John Herschel, however, saw the companion red, as others have done. These differences are doubtless due to imperfec- tions of the eye or the telescope/" In 1871 Burnham be- lieved he had discovered that the companion was an ex- ceedingly close double star. No one except Burnham himself succeeded in dividing it, and he 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 that the component stars were in rapid motion, and so, although he admitted that it might not be double after all, he advised that it should be watched for a few years longer. His confidence was justi- fied, for in 1898 Aitken, with the Lick telescope, saw and measured the distance of the extremely minute companion distance 0.17", p. 177. Rigel has been suspected of a slight degree of variabil- ity. It is evidently a star of enormous actual magnitude, for its parallax escapes trustworthy measurement. It can only be ranked among the very first of the light- givers of the visible universe. Spectroscopically it be- longs to a peculiar type which has very few representa- tives among the bright stars, and which has been thus described: " Spectra in which the hydrogen lines and the few metallic lines all appear to be of equal breadth and sharp definition." Rigel shows a line which some believe to represent magnesium; but while it has iron lines in its spectrum, it exhibits no evidence of the existence of any such cloud of volatilized iron as that which helps to en- velop the sun. directions become complicated. East and west can be readily identified by noticing the motion of a star through the field ; it moves toward the west and from the east. IN THE STARRY HEAVENS 23 For another test of what the three-inch will do turn to ?, the lower, or left-hand, star in the Belt. This is a triple, the magnitudes being second, sixth, and tenth. The sixth-magnitude star is about 2.5" from the primary, p. 149, and has a very peculiar color, hard to describe. It requires careful focusing to get a satisfactory view of this star with a three-inch telescope. Use magnifying powers up to two hundred and fifty diameters. With our four-inch the star is much easier, and the five-inch show r s it readily with a power of one hundred. The tenth-magni- tude companion is distant 56", p. 8, and may be glimpsed with the three-inch. Upon the whole, we shall find that we get more pleasing views of f Orionis with the four- inch glass. Just to the left of f, and in the same field of view with a very low power, is a remarkable nebula bearing the catalogue number 1227. We must use our five-inch on this with a low power, but with ? out of the field in order to avoid its glare. The nebula is exceedingly faint, and we can be satisfied if we see it simply as a hazy spot, although with much larger telescopes it has appeared at least half a degree broad. Tempel saw several centers of condensation in it, and traced three or four broad nebu- lous streams, one of which decidedly suggested spiral motion. The upper star in the Belt, 8, is double; distance, 53", p. 360; magnitudes, second and seventh very nearly; colors, white and green or blue. This, of course, is an easy object for the three-inch with a low magnifying power. It Would be useless to look for the two fainter companions of S, discovered by Burnham, even with our five-inch glass. 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 ex- 24 PLEASURES OF THE TELESCOPE amined is the little brilliant dangling below the right- hand end of the Belt, toward Rigel. It appears on the map as TJ. Spare no pains in getting an accurate focus, for here is something worth looking at, and unless you have a trained eye you will not easily see it. The star is double, magnitudes third and sixth, and the distance from center to center barely exceeds 1", p. 87. A little tremu- lousness of the atmosphere for a moment conceals the smaller star, although its presence is manifest from the peculiar jutting of light on one side of the image of the primary. But in an instant the disturbing undulations pass, the air steadies, the image shrinks and sharpens, and two points of piercing brightness, almost touch- ing one another, dart into sight, the more brilliant one being surrounded by an evanescent circle, a tiny ripple of light, which, as it runs round the star and then recedes, alternately embraces and releases the smaller companion. The wash of the light-waves in the atmosphere provokes many expressions of impatience from the astronomer, but it is often a beautiful phenomenon nevertheless. Between rj and 3 is a fifth-magnitude double star, 2 725, which is worth a moment's attention. The primary, of a reddish color, has a very 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 end of the Belt, where, just under f, we per- ceive the fourth-magnitude star o-. He must be a person of indifferent mind who, after looking with unassisted eyes at the modest glimmering of this little star, can see it as the telescope reveals it without a thrill of wonder and a cry of pleasure. The glass, as by a touch of magic, changes it from one into eight or ten stars. There are two quadruple sets three and a half minutes of arc apart. The first set exhibits a variety of beautiful colors. The IN THE STARRY HEAVENS 25 largest star, of fourth magnitude, is pale gray; the second in rank, seventh magnitude, distance 42", p. 61, presents a singular red, "grape-red" Webb calls it; the third, eighth magnitude, distance 12", p. 84, is blue; and the fourth, eleventh magnitude, distance 12", p. 236, is ap- parently white. Burnham has doubled the fourth-mag- nitude star, distance 0.23". The second group of four stars consists of three of the eighth to ninth magnitude, arranged in a minute triangle with a much fainter star near them. Between the two quadruple sets careful gaz- ing reveals two other very faint stars. While the five- inch gives a more satisfactory view of this wonderful mul- tiple star than any smaller telescope can do, the four-inch and even the three-inch would have shown it to us as a very beautiful object. However we look at them, there is an appearance of association among these stars, shin- ing with their contrasted colors and their various degrees of brilliance, which is significant of the diversity of con- ditions and circumstances under which the suns and worlds beyond the solar walk exist. From near the brightest member of the quartet. The Lick telescope has disclosed one or two other minute points of light associated with the Trapezium. But more interesting than the Trape- zium is the vast cloud, full of strange shapes, surrounding it. Nowhere else in the heavens is the architecture of a nebula so clearly displayed. It is an unfinished temple whose gigantic dimensions, while exalting the imagina- tion, proclaim the omnipotence of its builder. But though unfinished it is not abandoned. The work of crea- tion is proceeding within its precincts. There are stars apparently completed, shining like gems just dropped IN THE STAEBY HEAVENS 27 from the hand of the polisher, and around them are masses, eddies, currents, and swirls of nebulous matter yet to be condensed, compacted, and constructed into suns. It is an education in the nebular theory of the universe merely to look at this spot with a good tele- scope. If we do not gaze at it long and wistfully, and return to it many times with unflagging interest, we may be certain that there is not the making of an astronomer in us. Before quitting the Orion nebula do not fail to notice an eighth-magnitude star, a short distance northeast of the Great Nebula, and nearly opposite the broad opening in the latter that leads in toward the gap occupied by the Trapezium. This star is plainly enveloped in nebulosity, that is unquestionably connected with the larger mass of which it appears to form a satellite. At the lower end of the Sword is the star *, somewhat under the third magnitude. Our three-inch will show that it has a bluish companion of seventh or eighth mag- nitude, at a little more than 11" distance, p. 142, and the larger apertures will reveal a third star, of tenth mag- nitude, and reddish in color, distance 49", p. 103. Close by i we find the little double star 2 747, whose compo- nents are of five and a half and six and a half magnitudes respectively, and separated 36", p. 223. Above the up- permost star in the Sword is a small star cluster, No. 1184, which derives a special interest from the fact that it incloses a delicate double star, 2 750, whose larger com- ponent is of the sixth magnitude, while the smaller is of the ninth, and the distance is only 4.3", p. 59. We may try the four-inch on this object. Having looked at a (Betelgeuse), the great topaz star on Orion's right shoulder, and admired the splendor of its color, we may turn the four-inch upon the star 2 795, fre- 28 PLEASURES OF THE TELESCOPE quently referred to by its number as " 52 Orionis." It con- sists of one star of the sixth and another of sixth and a half magnitude, only 1.5" apart, p. 200. Having sepa- rated them with a power of two hundred and fifty diame- ters on the four-inch, we may try them with a high power on the three-inch. We shall only succeed this time if our glass is of first-rate quality and the air is perfectly steady. The star X in Orion's head presents an easy conquest for the three-inch, as it consists of a light-yellow star of magnitude three and a 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 tenth or eleventh magnitude one at 149", p. 278. These are tests for the five-inch, and we must not be disappointed if we do not succeed in seeing the smaller one even with that aperture. Other objects in Orion, to be found with the aid of our map, are: 2 627, a double star, magnitude six and a half and seven, distance 21", p. 260; O 2 98, otherwise named i Orionis, double, magnitude six and seven, distance 1", p. 180, requires five-inch glass; 2 652, double, magni- tudes six and a half and eight, distance 1.7", p. 184; p, double, magnitudes five and eight and a half, the latter blue, distance 7", p. 62, may be tried with a three-inch; T, triple star, magnitudes four, ten and a half, and eleven, distances 36", p. 249, and 36", p. 60. Burnham discov- ered that the ten-and-a-half magnitude star is again double, distance 4", p. 50. There is not much satisfac- tion in attempting T Orionis with telescopes of ordinary apertures; 2 Osfr, otherwise m Orionis, double, magnitudes five and a half (greenish) and seven, distance 31.7", p. 28, a pretty object; 2 728, otherwise A 32, double, magnitudes five and seven, distance, 0.5" or less, p. 206, a rapid IN THE STARRY HEAVENS 29 binary,* which is at present too close for ordinary tele- scopes, although it was once within their reach; 2 729, double, magnitudes six and eight, distance 2", p. 26, the smaller star pale blue try it with a four-inch, but five- inch is better; 2 816, double, magnitudes six and half and eight and a half, distance 4", p. 289; ^2, double, magni- tudes five and a half and eleven, distance 3", or a little less, p. 322; 905, star cluster, contains about twenty stars from the eighth to the eleventh magnitude; 1267, nebula, faint, containing a triple star of the eighth magni- tude, two of whose components are 51" apart, while the third is only 1.7" from its companion, p. 85; 1376, star cluster, small and crowded; 1361, star cluster, triangular shape, containing thirty stars, seventh to tenth magni- tudes, one of which is a double, distance 2.4". Let us now leave the inviting star-fields of Orion and take a glance at the little constellation of Lepus, crouch- ing at the feet of the mythical giant. We may begin with a new kind of object, the celebrated red variable R Le- poris (map No. 1). This star varies from the sixth or seventh magnitude to magnitude eight and a half in a period of four hundred and twenty-four days. Hind's picturesque description of its color has frequently been quoted. He said it is " of the most intense crimson, re- sembling a blood-drop on the black ground of the sky." It is important to remember that this star is reddest when faintest, so that if we chance to see it near its maximum of brightness it will not impress us as being crimson at all, but rather a dull, coppery red. Its spectrum indicates that it is smothered with absorbing vapors, a sun near extinction which, at intervals, experiences an accession of energy and bursts through its stifling envelope with ex- * The term "binary" is used to describe double stars which are in motion about their common center of gravity. 30 PLEASURES OF THE TELESCOPE plosive radiance, only to faint and sink once more. It is well to use our largest aperture in examining this star. We may also employ the. five-inch for an inspection of the double star i, whose chief component of the fifth mag- nitude is beautifully tinged with green. The smaller companion is very faint, eleventh magnitude, and the dis- tance is about 13", p. 337. Another fine double in Lepus is *, to be found just below *; the components are of the fifth and eighth mag- nitudes, pale yellow and blue respectively, distance 2.5", p. 360; the third-magnitude star a has a tenth-magnitude companion at a distance of 35", p. 156, and its neighbor ft (map No. 2), according to Burnham, is attended' by three eleventh-magnitude stars, two of which are at distances of 206", p. 75, and 240", p. 58, respectively, while the third is less than 3" from 0, p. 288 ; the star 7 (map No. 2) is a wide double, the distance being 94", and the magni- tudes four and eight. The star numbered 45 is a remark- able multiple, but the components are too faint to possess much interest for those who are not armed with very pow- erful telescopes. From Lepus we pass to Canis Major (map No. 2). There is no hope of our being able to see the companion of a (Sirius), at present (1901), even with our five-inch. Discovered by Alvan Clark with an eighteen-inch tele- scope in 1862, when its distance was 10" from the center of Sirius, this ninth-magnitude star has since been swal- lowed up in the blaze of its great primary. At first, it slightly increased its distance, and from 1868 until 1879 most of the measures made by different observers con- siderably exceeded 11". Then it began to close up, and in 1890 the distance scarcely exceeded 4". Burnham was the last to catch sight of it with the Lick telescope in that year. After that no human eye saw it until 1896, when it 32 PLEASURES OF THE TELESCOPE was rediscovered at the Lick Observatory. Since then the distance has gradually increased to nearly 5". Ac- cording to Burnham, its periodic time is about fifty-three years, and its nearest approach to Sirius should have taken place in the middle of 1892. Later calculations reduce the periodic time to forty-eight or forty-nine years. If we can not see the companion of the Dog Star with our instruments, we can at least, while admiring the splendor of that dazzling orb, reflect with profit upon the fact that although the companion is ten thousand times less bright than Sirius, it is half as massive as its brilliant neighbor. Imagine a subluminous body half as ponderous as the sun to be set revolving round it somewhere between Uranus and Neptune. Remember that that body would possess one hundred and sixty-five thousand times the gravitating energy of the earth, and that five hundred and twenty Jupiters would be required to equal its power of attrac- tion, and then consider the consequences to our easy-going planets! Plainly the solar system is not cut according to the Sirian fashion. We shall hardly find a more remark- able coupling of celestial bodies until we come, on another evening, to a star that began, ages ago, to amaze the thoughtful and inspire the superstitious with dread the wonderful Algol in Perseus. We may remark in passing that Sirius is the brightest representative of the great spectroscopic type I, which includes more than half of all the stars yet studied, and which is characterized by a white or bluish-white color, and a spectrum possessing few or at best faint metallic lines, but remarkably broad, black, and intense lines of hydrogen. The inference is that Sirius is surrounded by an enormous atmosphere of hydrogen, and that the in- tensity of its radiation is greater, surface for surface, than that of the sun. There is historical evidence to sup- /A^ THE STARRY HEAVENS 33 port the assertion, improbable in itself, that Sirius, with- in eighteen hundred years, has changed color from red to white. With either of our telescopes we shall have a feast for the eye when we turn the glass upon the star cluster No. 1454, some four degrees south of Sirius. Look for a red star near the center. Observe the curving rows so suggestive of design, or rather of the process by which this cluster was evolved out of a pre-existing nebula. You will recall the winding streams in the Great Nebula of Orion. Another star cluster worth a moment's attention is No. 1479, above and to the left of Sirius. We had bet- ter use the five-inch for this, as many of the stars are very faint. Not far away we find the double star p, whose components are of the fifth and eighth magnitudes, dis- tance 2.8", p. 343. The small star is pale blue. Cluster No. 1512 is a pleasing object with our largest aperture. In No. 1511 we have a faint nebula remarkable for the rows of minute stars in and near it. The star 7 is an irregular variable. In 1670 it is said to have almost dis- appeared, while at the beginning of the eighteenth cen- tury it was more than twice as bright as it is to-day. The reddish star 8 is also probably variable. In my " Astron- omy with an Opera Glass " will be found a cut showing a singular array of small stars partly encircling S. These are widely scattered by a telescope, even with the lowest power. Eastward from Canis Major we find some of the stars of Argo Navis. 2 1097, 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 Burn- ham, there is yet a fourth faint star at 31", p. 40. Some three degrees and a half below and to the left of the star IN THE STARRY HEAVENS 35 just examined is a beautiful star cluster, No. 1551. Nos. 1564, 1571, and 1630 are other star clusters well worth examination. A planetary nebula is included in 1564. With very powerful telescopes this nebula has been seen ring-shaped. 2 1146, otherwise known as 5 Navis, is a pretty double, colors pale yellow and blue, magnitudes five and seven, distance 3.25", p. 19. Our three-inch will suffice for this. 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 map No. 1. We shall begin with these. The most interesting and beautiful is 11, a fine triple star, magnitudes five, six, and seven, distances 7.4", p. 131, and 2.7", p. 103. Sir William Her- schel regarded this as one of the most beautiful sights in the heavens. It is a good object to try our three-inch on, although it should not be difficult for such an aperture. The star 4 is also a triple, magnitudes six, ten, and eleven, distances 3.4", p. 178, and 10", p. 244. We should glance at the star 5 to admire its fine orange color. In 8 we find a golden fifth-magnitude star, combined with a blue or lilac star of the seventh magnitude, distance 14", p. 24. 2 938 is a difficult double, magnitudes six and a half and twelve, distance 10", p. 210. 2 921 is double, magnitudes six and a half and eight, distance 16", p. 4. At the spot marked on the map 1424 we find an interesting cluster containing one star of the sixth magnitude. The remaining stars of Monoceros will be found on map No. 3. The double and triple stars to be noted are S, or 2 950 (which is also a variable and involved in a faint nebula), magnitudes six and nine, distance 2.5", p. 206; 21183, double, magnitudes five and a half and eight, dis- tance 31", p. 326; 2 1190, triple, magnitudes five and a half, ten, and nine, distances 31", p. 105, and 67", p. 244. 36 PLEASURES OF THE TELESCOPE 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; and 1637, interesting for the great number of ninth-magnitude tars that it contains. 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, a of Canis Minor, has several mi- nute stars in the same field of view. There is, besides, a companion which, although it was known to exist, no tele- scope was able to detect until November, 1896. It must be of immense mass, since its attraction causes perceptible perturba- tions in the motion of Procyon. Its magni- tude is eight and a half, 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's di- ameter, is an interest- PROCYON AND ITS NEIGHBORS. ing double. Our four- inch may separate it, and the five-inch is certain to do so. The magnitudes are seven and seven and a half or eight, distance 1.2", p. 133. This star is variously named 2 1126 and 31 Can. Min. Bode. Star No. 14 is a wide triple, mag- nitudes six, seven, and eight, distances 75, p. 65, and 115", p. 154. In the Head of Hydra we find 2 1245, a double of the sixth and seventh magnitudes, distance 10.5", p. 25. The larger star shows a fine yellow. In e we have a beautiful combination of a yellow with a blue star, magnitudes four IN THE STARRY HEAVENS 37 and eight, distance 3.4", p. 198. Finally, let us look at for a light test with the five-inch. The two stars com- posing it are of the fourth and twelfth magnitudes, dis- tance 50", p. 170. The brilliant constellations of Gemini and Taurus tempt us next, but warning clouds are gathering, and we shall do well to house our telescopes and warm our fingers by the winter fire. There will be other bright 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. THE zodiacal constellations of Gemini, Cancer, and Leo, together with their neighbors Auriga, the Lynx, Hydra, Sextans, and Coma Berenices, will furnish an abundance of occupation for our second night at the tele- scope. We shall begin, using our three-inch glass, with a, the chief 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 as its neighbor Pollux, P. Whether this fact is to be regarded as indicating that Castor was brighter than Pollux in 1603, when Bayer at- tached their Greek letters, is still an unsettled question. Castor may or may not be a variable,, but it is, at any rate, one of the most beautiful double stars in the heavens. A power of one hundred is amply sufficient to separate its components, whose magnitudes are about two and three, the distance between them being 6", p. 226. A slight yet distinct tinge of green, recalling that of the Orion nebula, gives a peculiar appearance to this couple. Green is one of the rarest colors among the stars. Castor be- longs to the same general spectroscopic type in which Sirius is found, but its lines of hydrogen are broader than those seen in the spectrum of the Dog Star. There is 38 40 PLEASURES OF THE TELESCOPE reason for thinking that it may be surrounded with a more extensive atmosphere of that gaseous metal called hydrogen than any other bright star possesses. There seems to be no doubt that the components of Castor are in revolution around their common center of gravity, although the period is uncertain, varying in different esti- mates all the way from two hundred and fifty to one thou- sand years; the longer estimate is probably not far from 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 our three-inch telescope for the four-inch, or, still better, the five-inch. Pollux has five faint compan- ions, of which we may expect to see three, as follows: Tenth magnitude, distance 175", p. 70; nine and a half magnitude, distance 206", p. 90, and ninth magnitude, distance 229", p. 75. Burnham has seen a star of thir- teen and a half magnitude, distance 43", p. 275, and has divided the tenth-magnitude star into two components, only 1.4" apart, the smaller being of the thirteenth mag- nitude, 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 a hundredfold more luminous than the sun, while its nearest companion may be a body smaller than our planet Jupiter, but shining, of course, by its own light. Its distance from Pollux, however, exceeds that of Jupiter from the sun in the ratio of about one hun- dred and thirty to one. In the double star IT we shall find a good light test for our three-inch aperture, the magnitudes being six and eleven, distance 22", p. 212. The four-inch will show that K is a double, magnitudes four and ten, distance 6", p. 232. The smaller star is of a delicate blue color, and it has been suspected of variability. That it may be vari- FROM GEMINI TO LEO AND HOUND ABOUT 41 able is rendered the more probable by the fact that in the immediate neighborhood of K there are three undoubted variables, S, T, and U, and there appears to be some mys- terious law of association which causes such stars to group themselves in certain regions. None of the vari- ables just named ever become visible to the naked eye, although they all undergo great changes of brightness, sinking from the eighth or ninth magnitude down to the thirteenth or even lower. The variable R, which lies con- siderably farther west, is well worth attention because of the remarkable change of color which it sometimes ex- hibits. It has been seen blue, red, and yellow in succes- sion. It varies from between the sixth and seventh mag- nitudes to less than the thirteenth in a period of about two hundred and forty-two days. Not far away we find a still more curious variable f; this is also an interesting triple star, its principal compo- nent being a little under the third magnitude, while one of the companions is of the seventh magnitude, distance 90", p. 355, and the other is of the eleventh magnitude or less, distance 65", p. 85. We should hardly expect to see the fainter companion with the three-inch. The principal star varies from magnitude three and seven tenths down to magnitude four and a half in a period of a little more than ten days. With the four- or five-inch we get a very pretty sight in 8, which appears split into a yellow and a purple star, magni- tudes three and eight, distance 7", p. 206. Near S, toward the east, lies One Of WONDERFUL NEBULA IN GEMINI (1532). the strangest of all the nebula. (See the figures 1532 on the map.) Our telescopes will show it to us only as a minute star surrounded with a nebu- lous atmosphere, but its appearance with instruments- 42 PLEASURES OF THE TELESCOPE of the first magnitude is so astonishing and at the same time so beautiful that I can not refrain from giving a brief description of it as I saw. it in 1893 with the great Lick telescope. In the center glittered the star, and spread evenly around it was a circular nebulous disk, pale yet sparkling and conspicuous. This disk was sharp- ly bordered by a narrow black ring, and outside the ring the luminous haze of the nebula again appeared, gradu- ally fading toward the edge to invisibility. The accom- panying cut, which exaggerates the brightness of the nebula as compared with the star, gives but a faint idea of this most singular object. If its peculiarities were within the reach of ordinary telescopes, there are few scenes in the heavens that would be deemed equally ad- mirable. In the star rj we have another long-period variable, which is also a double star; unfortunately the companion, being of only the tenth magnitude and distant less than 1" from its third-magnitude primary, is beyond the reach of our telescopes. But y points the way to one of the finest star clusters in the sky, marked 1360 on the map. The naked eye perceives that there is something remarkable in that place, and the opera glass faintly reveals its dis- tant splendors, but the telescope fairly carries us into its presence. Its stars are innumerable, varying from the ninth magnitude downward to the last limit of visibility, and presenting a wonderful array of curves which are highly interesting from the point of view of the nebular origin of such clusters. Looking backward in time, with that theory to guide us, we can see spiral lines of nebulous mist occupying the space that now glitters with inter- lacing rows of stars. It is certainly difficult to under- stand how such lines of nebula could become knotted with the nuclei of future stars, and then gradually be absorbed FROM GEMINI TO LEO AND ROUND ABOUT 43 into those stars; and yet, if such a process does not occur, what is the meaning of that narrow nebulous streak in the Pleiades along which five or six stars are strung like beads on a string? The surroundings of this cluster, 1360, as one sweeps over them with the telescope gradu- ally drawing toward the nucleus, have often reminded me of the approaches to such a city as London. Thicker and closer the twinkling points become, until at last, as the observer's eye follows the gorgeous lines of stars trend- ing inward, he seems to be entering the streets of a bril- .liantly lighted metropolis. Other objects in Gemini that we can ill miss are: A 6 , double, magnitudes three and eleven, distance 73", p. 76, colors yellow and blue; 15, double, magnitudes six and eight, distance 33", p. 205; 7, remarkable for array of small stars near it; 38, double, magnitudes six and eight, distance 6.5", p. 162, colors yellow and blue (very pretty); X, double, magnitudes four and eleven, distance 10", p. 30, color of larger star blue try with the five-inch; e, double, magnitudes three and nine, distance 110", p. 94. From Gemini we pass to Cancer. This constellation has no large stars, but its great cluster Praesepe (1681 on map No. 4) is easily seen as a starry cloud with the naked eye. With the telescope it presents the most brilliant ap- pearance with a very low power. It was one of the first objects that Galileo turned to when he had completed his telescope, and he wonderingly counted its stars, of which he enumerated thirty-six, and made a diagram showing their positions. The most interesting star in Cancer is , a celebrated triple. The magnitudes 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-inch glass in order satisfac- torily to separate the two nearest stars. The gravita- 44 PLEASURES OF THE TELESCOPE tional relationship of the three stars is very peculiar. The nearest pair revolve around their common center in about fifty-eight years, while the third star revolves with the other two, around a center common to all three, in a period of six or seven hundred years. But the movements of the third star are erratic, and inexplicable except upon the hypothesis advanced by Seeliger, that there is an in- visible, or dark, star near it by whose attraction its mo- tion is perturbed. In endeavoring to picture the condition of things in f Cancri we might imagine our sun to have a companion sun, a half or a third as large as itself, and situated within what may be called planetary distance, circling with it around their center of gravity; while a third sun, smaller than the second and several times as far away, and accom- panied by a black or non-luminous orb, swings with the first two around another center of motion. There you would have an entertaining complication for the inhabit- ants of a system of planets! Other objects in Cancer are: 2 1223, double star, mag- nitudes six and six and a half, distance 5", p. 214; 2 1291, double, magnitudes both six, distance 1.3", p. 328 four- inch should split it; *, double, magnitudes four and a half and six and a half, distance 30", p. 308 ; 66, double magni- tudes six and nine, distance 4.8", p. 136; 21311, double, magnitudes both about the seventh, distance 7", p. 200 ; 1712, star cluster, very beautiful with the five-inch glass. The constellation of Auriga may next command our attention (map No. 5). The calm beauty of its leading star Capella awakens an admiration that is not dimin- ished by the rivalry of Orion's brilliants glittering to the south of it. Although Capella must be an enormously greater sun than ours, its spectrum bears so much resem- blance to the solar spectrum that a further likeness of 46 PLEASURES OF THE TELESCOPE condition is suggested. No close telescopic companion to Capella has been discovered. A ninth-magnitude com- panion, distant 159", p. 146, and two others, one of twelfth magnitude at 78", p. 317, and the other of thir- teenth magnitude at 126", p. 183, may be distant satel- lites of the great star, but not planets in the ordinary sense, since it is evident that they are self-luminous. It is a significant fact that most of the first-magnitude stars have faint companions which are not so distant as altogether to preclude the idea of- physical relation- ship. But while Capella has no visible companion, Campbell, of the Lick Observatory, has lately discovered that it is a conspicuous example of a peculiar class of binary stars only detected within the closing decade of the nineteenth century. The nature of these stars, called spectroscopic binaries, may perhaps best be described while we turn our attention from Capella to the second star in Auriga (Menkalina), which not only belongs to the same class, but was the first to be discovered. Neither our tele- scopes, nor any telescope in existence, can directly reveal the duplicity of fi Auriga to the eye i. e., we can not see the two stars composing it, because they are so close that their light remains inextricably mingled after the highest practicable magnifying power has been ap- plied in the effort to separate them. But the spectro- scope shows that the star is double and that its compo- nents are in rapid revolution around one another, com- pleting their orbital swing in the astonishingly short period of four days! The combined mass of the two stars is estimated to be two and a half times the mass of the sun, and the distance between them, from center to center, is about eight million miles. The manner in which the spectroscope revealed the FROM GEMINI TO LEO AND ROUND ABOUT 47 existence of two stars in /9 Auriga? is a beautiful illustra- tion of the unexpected and, so to speak, automatic appli- cation of an old principle in the discovery of new facts not looked for. It was noticed at the Harvard Observa- tory that the lines in the photographed spectrum of /Q Auriga? (and of a few other stars to be mentioned later) appeared single in some of the photographs and double in others. Investigation proved that the lines were doubled at regular intervals of about two days, and that they appeared single in the interim. The explanation was not far to seek. It is known that all stars which are approaching us have their spectral lines shifted, by virtue of their motion of approach, toward the violet end of the spectrum, and that, for a similar reason, all stars which are receding have their lines shifted toward the red end of the spectrum. Now, suppose two stars to be revolving around one another in a plane horizontal, or nearly so, to the line of sight. When they are at their greatest angu- lar distance apart as seen from the earth one of them will evidently be approaching at the same moment that the other is receding. The spectral lines of the first will therefore be shifted toward the violet, and those of the second will be shifted toward the red. Then if the stars, when at their greatest distance apart, are still so close that the telescope can not separate them, their light will be combined in the spectrum; but the spectral lines, being simultaneously shifted in opposite directions, will neces- sarily appear to be doubled. As the revolution of the stars continues, however, it is clear that their motion will soon cease to be performed in the line of sight, and will become more and more athwart that line, and as this oc- curs the spectral lines will gradually assume their normal position and appear single. This is the sequence of phe- nomena in /3 Auriga?. And the same sequence is found in 48 PLEASURES OF THE TELESCOPE Capella and in several other more or less conspicuous stars in various parts of the heavens. Such facts, like those connecting rows and groups of stars with masses and spiral lines of -nebula are obscure signboards, indicating the opening of a way which, start- ing in an unexpected direction, leads deep into the mys- teries of the universe. Southward from $ we find the star 0, which is a beauti- ful quadruple. We shall do best with our five-inch here, although in a fine condition of the atmosphere the four- inch might suffice. The primary is of the third magni- tude; the first companion is of magnitude seven and a half, distance 2", p. 5; the second, of the tenth magni- tude, distance 45", p. 292; and the third, of the tenth magnitude, distance 125", p. 350. We should look at the double 2 616 with one of our larger apertures in order to determine for ourselves what the colors of the components are. There is considerable diversity of opinion on this point. Some say the larger star is pale red and the smaller light blue; others con- sider the color of the larger star to be greenish, and some have even called it white. The magnitudes are five and nine, distance 6", p. 350. . Auriga contains several noteworthy clusters which will be found on the map. The most beautiful of these is 1295, in which about five hundred stars have been counted. The position of the new star of 1892, known as Nova Aurigse, is also indicated on the map. While this never made a brilliant appearance, it gave rise to a greater va- riety of speculative theories than any previous phenome- non of the kind. Although not recognized until January 24, 1892, this star, as photographic records prove, was in existence on December 9, 1891. At its brightest it barely exceeded magnitude four and a half, and its maximum FROM GEMINI TO LEO AND ROUND ABOUT 49 occurred within ten days after its first recognition. When discovered it was of the fifth magnitude. It was last seen in its original form with the Lick telescope on April 26th, when it had sunk to the lowest limit of visibil- ity. To everybody's astonishment it reappeared in the following August, and on the 17th of that month was seen shining with the light of a tenth-magnitude star, but pre- senting the spectrum of a nebula! Its visual appearance in the great telescope was now also that of a planetary nebula. Its spectrum during the first period of its visi- bility had been carefully studied, so that the means ex- isted for making a spectroscopic comparison of the phe- nomenon in its two phases. During the first period, when only a stellar spectrum was noticed, remarkable shiftings of the spectral lines occurred, indicating that two and perhaps three bodies were concerned in the production of the light of the new star, one of which was approaching the earth, while the other or the others receded with ve- locities of several hundred miles per second! On the revival in the form of a planetary nebula, while the char- acter of the spectrum had entirely changed, evidences of rapid motion in the line of sight remained. But what was the meaning of all this? Evidently a catastrophe of some kind had occurred out there in space. The idea of a collision involving the transformation of the energy of motion into that of light and heat suggests itself at once. But what were the circumstances of the collision? Did an extinguished sun, flying blindly through space, plunge into a vast cloud of meteoric parti- cles, and, under the lashing impact of so many myriads of missiles, break into superficial incandescence, while the cosmical wrack through which it had driven remained glowing with nebulous luminosity? Such an explanation has been offered by Seeliger. Or was Vogel right when 50 PLEASURES OF THE TELESCOPE he suggested that Nova Auriga? could be accounted for by supposing that a wandering dark body had run into colli- sion with a system of planets surrounding a decrepit sun (and therefore it is to be "hoped uninhabited), and that those planets had been reduced to vapor and sent spin- ning by the encounter, the second outburst of light being caused by an outlying planet of the system falling a prey to the vagabond destroyer? Or some may prefer the ex- planation, based on a theory of Wilsing's, that two great bodies, partially or wholly opaque and nonluminous at their surfaces, but liquid hot within, approached one an- other so closely that the tremendous strain of their tidal attraction burst their shells asunder so that their bowels of fire gushed briefly visible, amid a blaze of spouting vapors. And yet Lockyer thinks that there was no solid or semisolid mass concerned in the phenomenon at all, but that what occurred was simply the clash of two immense swarms of meteors that had crossed one another's track. Well, where nobody positively knows, everybody has free choice. In the meantime, look at the spot in the sky where that little star made its appearance and under- went its marvelous transformation, for, even if you can see no remains of it there, you will feel your interest in the problem it has presented, and in the whole subject of astronomy, greatly heightened and vivified, as the visitor to the field of Waterloo becomes a lover of history on the spot. The remaining objects of special interest in Auriga may be briefly mentioned: 26, triple star, magnitudes five, eight, and eleven, distances 12", p. 268, and 26", p. 113; 14, triple star, magnitudes five, seven and a half, and eleven, distances 14", p. 224, and 12.6", p. 342, the last difficult for moderate apertures; X, double, magnitudes five and nine, distance 121", p. 13; e, variable, generally FROM GEMINI TO LEO AND HOUND ABOUT 51 of third magnitude, but has been seen of only four and a half magnitude; 41, double, magnitudes five and six, distance 8", p. 354; 996, 1067, 1119, and 1166, clusters all well worth inspection, 1119 being especially beautiful. The inconspicuous Lynx furnishes some fine telescopic objects, all grouped near the northwestern corner of the constellation. Without a six-inch telescope it would be a waste of time to attack the double star 4, whose compo- nents are of sixth and eighth magnitudes, distance 0.8", p. 103; but its neighbor, 5, a fine triple, is within our reach, the magnitudes being six, ten, and eight, distances 30", p. 139, and 96", p. 272. In 12 Lyncis we find one of the most attractive of triple stars, which in good seeing weather is not beyond the powers of a three-inch glass, although we shall have a far more satisfactory view of it with the four-inch. The components are of the sixth, seventh, and eighth magnitudes, distances 1.4", p. 117, and 8.7", p. 304. A magnifying power which just suffices clearly to separate the disks of the two nearer stars makes this a fine sight. A beautiful contrast of colors belongs to the double star 14, but unfortunately the star is at present very close, the distance between its sixth and seventh magnitude components not exceeding 0.8", posi- tion angle 64. 2 958 is a pretty double, both stars being of the sixth magnitude, distance 5", p. 257. Still finer is 2 1009, a double, whose stars are both a little above the seventh magnitude and nearly equal, distance 3", p. 156. A low power suffices to show the three stars in 19, their magnitudes being six and a half, seven and a half, and eight, distances 15", p. 312, and 215", p. 358. Webb de- scribes the two smaller stars as plum-colored. Plum-col- ored suns! At the opposite end of the constellation are two fine doubles, 2 1333, magnitudes six and a half and seven, dis- 52 PLEASURES OF THE TELESCOPE tance 1.4", p. 39; and 38, magnitudes four and seven, dis- tance 2.9", p. 235. Under the guidance of map No. 6 we turn to Leo, which contains one of the leading gems anjbng the double stars, 7, whose components, of the second and fourth magnitudes, are respectively yellow and green, the green star, accord- ing to some observers, having a peculiar tinge of red. Their distance apart is 3.7", p. 118, and they are un- doubtedly in revolution about a common center, the prob- able period being about four hundred years. The three- inch glass should separate them easily when the air is steady, and a pleasing sight they are. The star i is a closer double, and also very pretty, mag- nitudes four and eight, colors lemon and light blue, dis- tance 2.17", p. 53. Other doubles are T, magnitudes five and seven, distance 95", p. 170; 88, magnitudes seven and nine, distance 15", p. 320; 90, triple, magnitudes six, seven and a half, and ten, distance, 3.5", p. 209, and 59", p. 234; 54, magnitudes four and a half and seven, dis- tance 6.2", p. 102; and 49, magnitudes six and nine, dis- tance 2.4", p. 158. Leo contains a remarkable variable star, K, deep red in color, and varying in a space of a hundred and forty- four days from the fifth to the tenth magnitude. It has also several nebulae, of which only one needs special men- tion, No. 1861. This is spindle-shaped, and large tele- scopes show that it consists of three nebula?. The ob- server with ordinary instruments finds little to see and little to interest him in these small, faint nebulae. We may just glance at two double stars in the small constellation of Sextans, 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. Coma Berenices (map No. 6) includes several interest- 54 PLEASURES OF THE TELESCOPE ing objects. Let us begin with the star 2, a double, of magnitudes six and seven and a half, distance 3.6", p. 240. The color of the smaller s^tar is lilac. This hue, although not extremely uncommon among ; double stars elsewhere, recurs again and again, with singular persistence, in this little constellation. For instance, in the very next star that we look at, 12, we find a double whose smaller com- ponent is lilac. The magnitudes in 12 are five and eight, distance 66", p. 168. So also the wide double 17, magni- tudes five and a half and six, distance 145", exhibits a tinge of lilac in the smaller component; the triple 35, mag- nitudes five, eight, and nine, distances 1", p. 77, and 28.7", p. 124, has for colors yellow, lilac, and blue, and the double 24, magnitudes five and six, distance 20", p. 270, combines an orange with a lilac star, a very striking and beautiful contrast. We should make a mistake if we regarded this wonderful distribution of color among the double stars as accidental. It is manifestly expressive of their physical condition, although we can not yet decipher its exact meaning. The binary 42 Coma? Berenicis is too close for ordinary telescopes, but it is highly interesting as an intermediate between those pairs which the telescope is able to sepa- rate and those like ft Aurigse which no magnifying power can divide, but which reveal the fact that they are double by the periodical splitting of their spectral lines. The orbit in 42 Comae Berenicis is a very small one, so that even when the components are at their greatest distance apart they can not be separated by a five- or six-inch glass. Burnham, using the Lick telescope, in 1890 made the dis- tance 0.7"; Hall, using the Washington telescope, in 1891 made it a trifle more than 0.5". He had measured it in 1886 as only 0.27". The period of revolution is believed to be about twenty-five years. 56 PLEASURES OF THE TELESCOPE In Coma Berenices there is an outlying field of the mar- velous nebulous region of Virgo, which we may explore on some future evening. .But the . nebulae in Coma are very faint, and, for an amateur, hardly worth the trouble required to pick them up. The two clusters included in the map, 2752 and 3453, are bright enough to repay inspec- tion with our largest aperture. Although Hydra is the largest constellation in the heavens, extending about seven hours, or 105, in right ascension, it contains comparatively few objects of inter est, and most of these are in the head or western end of the constellation, which we examined during our first night at the telescope. In the central portion of Hydra, represented on map No. 7, we find its leading star a, some- times called Alphard, or Cor Hydra?, a bright second-mag- nitude star that has been suspected of variability. It has a decided orange tint, and is accompanied, at a distance of 281", p. 153, by a greenish tenth-magnitude star. Bu. 339 is a fine double, magnitudes eight and nine and a half, distance 1.3", p. 216. The planetary nebula 2102 is about V in diameter, pale blue in color, and worth looking at, because it is brighter than most objects of its class. Tern- pel and Secchi have given wonderful descriptions of it, both finding multitudes of stars intermingled with nebu- lous matter. For a last glimpse at celestial splendors for the night, let us turn to the rich cluster 1630, in Argo, just above the place where the stream of the Milky Way here bright in mid-channel and shallowing toward the shores separates into two or three currents before disappearing behind the horizon. It is by no means as brilliant as some of the star clusters we have seen, but it gains in beauty and im- pressiveness from the presence of one bright star that seems to captain a host of inferior luminaries. CHAPTER IV VIRGO AND HER NEIGHBORS ..." that region Where still by night is seen The Virgin goddess near to bright Bo6tes." POSTE'S ARATUS. FOLLOWING the order of right ascension, we come next to the little constellations Crater and Corvus, which may be described as standing on the curves of Hydra (map No. 8). Beginning with Crater, let us look first at a, a yellow fourth-magnitude star, near which is a celebrated red variable R. With a low power w r e can see both a and R in the same field of view, like a very wide double. There is a third star of ninth magnitude, and bluish in color, near R on the side toward a. R is variable both in color and light. When reddest, it has been described as "scarlet," "crimson," and "blood-colored"; when palest, it is a deep orange-red. Its light variation has a period the precise length of which is not yet known. The cycle of change is included between the eighth and ninth mag- nitudes. While our three-inch telescope suffices to show R, it is better to use the five-inch, because of the faintness of the star. When the color is well seen, the contrast with a is very pleasing. There is hardly anything else in Crater to interest us, and we pass over the border into Corvus, and go at once to its chief attraction, the star 8. The components of this 5 57 VIRGO AND HER NEIGHBORS 59 beautiful double are of magnitudes three and eight; dis- tance 24", p. 211; colors yellow and purple. The night being dark and clear, we take the five-inch and turn it on the nebula 3128, which the map shows just under the border of Corvus in the edge of Hydra. Her- schel believed he had resolved this into stars. It is a faint object and small, not exceeding one eighth of the moon's diameter. Farther east in Hydra, as indicated near the left-hand edge of map No. 8, is a somewhat remarkable variable, R Hydra3. This star occasionally reaches magnitude three and a half, while at minimum it is not much above the tenth magnitude. Its period is about four hundred and twenty-five days. While we have been examining these comparatively barren regions, glad to find one or two colored doubles to relieve the monotony of the search, a glittering white star has frequently drawn our eyes eastward and upward. It is Spica, the great gem of Virgo, and, yielding to its attraction, we now enter the richer constellation over which it presides (map No. 9). Except for its beauty, which every one must admire, Spica, or a Virginis, has no special claim upon our attention. Some evidence has been obtained that, like /3 Auriga3 and Capella, it revolves with an invisible companion of great mass in an orbit only six million miles in diameter. Spica's spectrum resembles that of Sirius. The faint star which our larger apertures show about 6' northeast of Spica is of the tenth mag- nitude. Sweeping westward, we come upon 2 1669, a pretty little double with nearly equal components of about the sixth magnitude, distance 5.6", p. 124. But our interest is not fully aroused until we reach 7, a star with a history. The components of this celebrated binary are both nearly 60 PLEASURES OF THE TELESCOPE of the third magnitude, distance about 5.8", p. 150. They revolve around their common center in something less than two hundred years. According to some authorities, the period is one hundred and seventy years, but it is not yet certainly ascertained. It was noticed about the be- ginning of the seventeenth century that 7 Virginis was double. In 1836 the stars were so close together that no telescope then in existence was able to separate them, although it is said that the disk into which they had merged was elongated at Pulkowa. In a few years they became easily separable once more. If the one-hundred- and-seventy-year period is correct, they should continue to get farther apart until about 1921. According to Asaph Hall, their greatest apparent distance is 6.3", and their least apparent distance 0.5"; consequently, they will never again close up beyond the separating power of ex- isting telescopes. There is a great charm in watching this pair of stars even with a three-inch telescope not so much on account of what is seen, although they 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 that makes a stone fall to the ground and compels the earth to swing round the sun. In 6 we discover a fine triple, magnitudes four and a half, nine, and ten; distances 7", p. 345, and 65", p. 295. The ninth-magnitude star has been described as " violet," but such designations of color are often misleading when the star is very faint. On the other hand it should not be assumed that a certain color does not exist because the observer can not perceive it, for experience shows that there is a wide difference among observers in the power of the eye to distinguish color. I have known persons who could not perceive the difference of hue in some of 62 PLEASURES OF THE TELESCOPE the most beautifully contrasted colored doubles to be found in the sky. I am acquainted with an astronomer of long experience in the use of telescopes, whose eye is so deficient in color sense that he d'enies that there are any decided colors amongftje' stars. Such persons miss one of the finest pleasures of the telescope. In examining 6 Virginis we shall do best to use our largest aperture, viz., the five-inch. Yet Webb records that all three of the stars in this triple have been seen with a telescope of only three inches aperture. The amateur must remember in such cases how T much depends upon practice as well as upon the condition of the atmosphere. There are lamen- tably few nights in a year when even the best telescope is ideally perfect in performance, but every night's obser- vation increases the capacity of the eye, begetting a kind of critical judgment which renders it to some extent inde- pendent of atmospheric vagaries. It will also be found that the idiosyncrasies of the observer are reflected in his instrument, w T hich seems to have its fits of excellence, its inspirations so to speak, while at other times it behaves as if all its wonderful powers had departed. Another double that perhaps we had better not try with less than four inches aperture is 84 Virginis. The magnitudes are six and nine; distance, 3.5", p. 233. Col- ors yellow and blue. 2 1846 is a fifth-magnitude star with a tenth-magnitude companion, distance only 4", p. 108. Use the five-inch. And now we approach something that is truly marvel- ous, the " Field of the Nebula?." This strange region, lying mostly in the constellation Virgo, is roughly out- lined by the stars /3, 77, 7, S, and e, which form two sides of a square some 15 across. It extends, however, for some distance into Coma Berenices, while outlying nebula? be- longing to it are also to be found in the eastern part of VIRGO AND HER NEIGHBORS 63 Leo. Unfortunately for those who expect only brilliant revelations when they look through a telescope, this throng of nebula? consists of small and inconspicuous wisps 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 the brightest are faint objects when seen with the largest of our telescopes. Why do they congregate thus? That is the question which lends an interest to the assemblage that no individual member of it could alone command. It is a mystery, but beyond question it is explicable. The explanation, however, is yet to be discovered. The places of only three of the nebula? are indicated on the map. No. 2806 has been described as resembling in shape a shuttle. Its length is nearly one third of the moon's diameter. It is brightest near the center, and has several faint companions. No. 2961 is round, in diame- ter, and is accompanied by another round nebula in the same field of view toward the south. No. 3105 is double, and powerful telescopes show two more ghostly compan- ions. There is an opportunity for good and useful work in a careful study of the little nebula? that swim into view all over this part of Virgo. Celestial photography has triumphs in store for itself here. Scattered over and around the region where the nebu- la? are thickest we find eight or nine variable stars, three of the most remarkable of which, K, S, and U, may be found on the map. R is very irregular, sometimes attain- ing magnitude six and a half, while at other times its maximum brightness does not exceed that of an eighth- magnitude star. At minimum it sinks to the tenth or eleventh magnitude. Its period is one hundred and forty- five days. U varies from magnitude seven or eight down to magnitude twelve or under and then regains its light, 64: PLEASURES OF THE TELESCOPE in a period of about two hundred and seven days. S is interesting for its brilliant red color. When brightest, it exceeds the sixth magnitude, but at some of its maxima the magnitude is hardly greater 'than the eighth. At minimum it goes below the twelfth magnitude. Period, three hundred and seventy-six days. Next east of Virgo is Libra, which contains a few notable objects (map No. 10). The star a has a fifth-mag- nitude companion, distant about 230", which can be easily seen with an opera glass. At the point marked A on the map is a curious multiple star, sometimes referred to by its number in Piazzi's catalogues as follows: 212 P. xiv. The two principal stars are easily seen, their magnitudes being six and seven and a half; distance 15", p. 290. Burnham found four other faint companions, for which it would be useless for us to look. The remarkable thing is that these faint stars, the nearest of which is distant about 50" from the largest member of the group and the farthest about 129", do not share, according to their dis- coverer, in the rapid proper motion of the two main stars. In i we find a double a little difficult for our three-inch. The components are of magnitudes four and a half and nine, distance 57", p. 110. Burnham discovered that the ninth-magnitude star consists of two of the tenth less than 2" apart, p. 24. No astronomer who happens to be engaged in this part of the sky ever fails, unless his attention is absorbed by something of special interest, to glance at /? Libra?, which is famous as the only naked-eye star having a decided green color. The hue is pale, but manifest.* The star is a remarkable variable, belonging to what is called the Algol type. Its period, according to Chan- * Is the slight green tint perceptible in Sirius variable ? I am sometimes dis- posed to think it is. 66 PLEASURES OF THE TELESCOPE dler, is 2 days 7 hours, 51 minutes, 22.8 seconds. The time occupied by the actual changes is about twelve hours. At maximum the star is of magnitude five and at minimum of magnitude 6.2. We may now conveniently turn northward from Virgo in order to explore Bootes, one of the most interesting of the constellations (map No. 11). Its leading star a, Arctu- rus, is the brightest in the northern hemisphere. Its pre- cedence over its rivals Vega and Capella, long in dispute, has been settled by the Harvard photometry. You notice that the color of Arcturus, when it has not risen far above the horizon, is a yellowish red, but when the star is near mid-heaven the color fades to light yellow. The hue is possibly variable, for it is recorded that in 1852 Arctu- rus appeared to have nearly lost its color. If it should eventually turn white, the fact would have an important bearing upon the question whether Sirius was, as alleged, once a red or flame-colored star. But let us sit here in the starlight, for the night is balmy, and talk about Arcturus, which is perhaps actually the greatest sun within the range of terrestrial vision. Its parallax is so minute that the consideration of the tremendous size of this star is a thing that the imagina- tion can not placidly approach. Calculations, based on its assumed distance, which show that it outshines the sun several thousand times, may be no exaggeration of the truth! It is easy to make such a calculation. One of Dr. Elkin's parallaxes for Arcturus is 0.018". That is to say, the dis- placement of Arcturus due to the change in the observer's point of view when he looks at the star first from one side and then from the other side of the earth's orbit, 186,000,000 miles across, amounts to only eighteen one- thousandths of a second of arc. We can appreciate how small that is when we reflect that it is about equal to the ,A MAJOR RONA BOREALIS SERPENS :ANES VENATICI MAP No. 11. 68 PLEASURES OF THE TELESCOPE apparent distance between the heads of two pins placed an inch apart and viewed from a distance of a hundred and eighty miles! Assuming this estimate of the parallax of Arcturus, let us see how it will enable us to calculate the probable size or light-giving power of the star as compared with the sun. The first thing to do is to multiply the earth's dis- tance from the sun, which may be taken at 93,000,000 miles, by 206,265, the number of seconds of arc in a radian, the base of circular measure, and then divide the product by the parallax of the star. Performing the multiplica- tion and division, we get the following: 19,182,645,000,000 _ 1)065>790>250)000>000 . The quotient represents miles! Call it, in round numbers, a thousand millions of millions of miles. This is about 11,400,000 times the distance from the earth to the sun. Now for the second part of the calculation: The amount of light received on the earth from some of the brighter stars has been experimentally compared w r ith the amount received from the sun. The results differ rather widely, but in the case of Arcturus the ratio of the star's light to sunlight may be taken as about one twenty-five- thousand-millionth i. e., 25,000,000,000 stars, each equal to Arcturus, would together shed upon the earth as much light as the sun does. But we know that light varies in- versely as the square of the distance; for instance, if the sun were twice as far away as it is, its light would be diminished for us to a quarter of its present amount. Suppose, then, that we could remove the earth to a point midway between the sun and Arcturus, we should then be 5,700,000 times as far from the sun as we now are. In order to estimate how much light the sun would send us from that distance we must square the number 5,700,000 VIRGO AND HER NEIGHBORS 69 and then take the result inversely, or as a fraction. We thUS get 32,490,000,000,000, re P reseptin g the ratio of the sun's light at half the distance of Arcturus to that at its real distance. But while receding from the sun we should be approaching Arcturus. We should get, in fact, twice as near to that star as we were before, and therefore its light would be increased for us fourfold. Now, if the amount of sunlight had not changed, it would exceed the light of Arcturus only a quarter as much as it did before, or in the ratio of 25 ' 000 '0 ' 000 = 6,250,000,000 to 1. But, as we have seen, the sunlight would diminish through in- crease of distance to one 32,490,000,000,000th part of its original amount. Hence its altered ratio to the light of Arcturus would become 6,250,000,000 to 32,490,000,000,000, or 1 to 5,198. This means that if the earth were situated midway between the sun and Arcturus, it would receive 5,198 times as much, light from that star as it would from the sun! It is quite probable, moreover, that the heat of Arcturus exceeds the solar heat in the same ratio, for the spectroscope shows that although Arcturus is sur- rounded with a cloak of metallic vapors proportionately far more extensive than the sun's, yet, smothered as the great star seems in some respects to be, it rivals Sirius itself in the intensity of its radiant energy. If we suppose the radiation of Arcturus to be the same per unit of surface as the sun's, it follows that Arcturus exceeds the sun about 375,000 times in volume, and that its diameter is no less than 62,350,000 miles! Imagine the earth and the other planets constituting the solar system removed to Arcturus and set revolving around it in orbits of the same forms and sizes as those in which they circle 70 PLEASURES OF THE TELESCOPE about the sun. Poor Mercury! For that little planet it would indeed be a jump from the frying pan into the fire, because, as it rushed to perihelion, Mercury would plunge more than 2,500,000 miles beneath the surface of the giant star. Venus and the earth would melt like snowflakes at the mouth of a furnace. Even far-away Neptune, the remotest member of the system, would swelter in torrid heat. But stop! Look at the sky. Observe how small and motionless the disks of the stars have become. Back to the telescopes at once, for this is a token that the atmos- phere is steady, and that " good seeing " may be ex- pected. It is fortunate, for we have some delicate work before us. The very first double star we try in Bootes, X 1772, requires the use of the four-inch, and the five-inch shows it more satisfactorily. The magnitudes are sixth and ninth, distance 5", p. 140. On the other side of Arc- turus we find f, a star that we should have had no great difficulty in separating thirty years ago, but which has now closed up beyond the reach even of our five-inch. The magnitudes are both fourth, and the distance less than a quarter of a second; position angle changing. It is ap- parently a binary, and if so will some time widen again, but its period is unknown. The star 279, also known as 5 1910, near the southeastern edge of the constellation, is a pretty double, each component being of the seventh mag- nitude, distance 4", p. 212. Just above f we come upon TT, an easy double for the three-inch, magnitudes four and six, distance 6" p. 99. Next is f, a yellow and purple pair, whose magnitudes are respectively five and seven, distance less than 3", p. 200. This is undoubtedly a bi- nary with a period of revolution of about a hundred and thirty years. Its distance decreased about V between 1881 and 1891. It was still decreasing in 1899, when it VIRGO AND HER NEIGHBORS 71 had become 2.5". The orbital swing is also very apparent in the change of the position angle. The telescopic gem of Bootes, and one of " the flowers of the sky," is e, also known as Mirac. When well seen, as we shall see it to-night, e Bootis is superb. The mag- nitudes of its two component stars are two and a half (ac- cording to Hall, three) and six. The distance is about 2.8", p. 326. The contrast of colors bright orange yellow, set against brilliant emerald green is mag- nificent. There are very few doubles that can be com- pared with it in this respect. The three-inch will sepa- rate it, but the five-inch enables us best to enjoy its beauty. It appears to be a binary, but the motion is very slow, and nothing certain is yet known of its period. In 8 we have a very wide and easy double; magnitudes three and a half and eight and a half, distance 110", p. 75. The smaller star has a lilac hue. We can not hope with any of our instruments to see all of the three stars contained in /*, but two of them are easily seen; magni- tudes four and seven, distance 108", p. 172. The smaller star is again double; magnitudes seven and eight, dis- tance 0.77", p. 88. It is clearly a binary, with a long period. A six-inch telescope that could separate this star at present would be indeed a treasure. % 1926 is another object rather beyond our powers, on account of the con- trast of magnitudes. These are six and eight and a half; distance 1.3", p. 256. Other doubles are: 44 (21909), magnitudes five and six, distance 4.8", p. 240; 39 (1890), magnitudes both nearly six, distance 3.6", p. 45. Smaller star light red; t, magnitudes four and a half and seven and a half, distance 38", p. 33; *, magnitudes five and a half and eight, dis- tance 12.7", p. 238. Some observers see a greenish tinge in the light of the larger star, the smaller one being blue. 72 PLEASURES OF THE TELESCOPE There are one or two interesting things to be seen in that part of Canes Venatici which is represented on map No. 11. The first of these is the star cluster 3936. This will reward a good look with the five-inch. With large telescopes as many as one thousand stars have been dis- cerned packed within its globular outlines. The star 25 (2 1768) is a close binary with a period estimated at one hundred and twenty-five years. The magnitudes are six and seven or eight, distance about 1", p. 137. We may try for this with the five-inch, and if we do not succeed in separating the stars we may hope to do so some time, for the distance between them is increasing. Although the nebula 3572 is a very wonderful object, we shall leave it for another evening. Eastward from Bootes shines the circlet of Corona Borealis, whose form is so strikingly marked out by the stars that the most careless eye perceives it at once. Although a very small constellation, it abounds with in- teresting objects. We begin our attack with the five-inch on S 1932, but not too confident that we shall come off victors, for this binary has been slowly closing for many years. The magnitudes are six and a half and seven, dis- tance 0.84", p. 150. Not far distant is another binary, at present beyond our powers, rj. Here the magnitudes are both six, distance 0.65", p. 3. Hall assigns a period of forty years 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, the star 7. What has previ- ously been said about 42 Coma? Berenicis applies in a measure to this star also. It, too, has a comparatively small orbit, and its components are never seen widely separated. In 1826 their distance was 0.7"; in 1880 they could not be split; in 1891 the distance had increased to VIRGO AND HER NEIGHBORS 73 0.36", and in 1894 it had become 0.53", p. 123. But in 1899 Lewis made the distance only 0.43". The period has been estimated at one hundred years. While the group of double stars in the southern part of Corona Borealis consists, as we have seen, of remark- ably close binaries, another group in the northern part of the same constellation comprises stars that are easily separated. Let us first try ?. The powers of the three- inch are 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 cr ? whose magnitudes are five and six, dis- tance 4", p. 206. With the five-inch we may look for a second companion of the tenth magnitude, distance 54", p. 88. It is thought highly probable that 2 , each of which has a faint companion. With the five-inch we may be able to see the companion of z> 2 , the more southerly of the pair. The magnitude of the companion is variously given as 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 which spectroscopic analysis was ap- plied. When first noticed, on May 12, 1866, this star was of the second magnitude, fully equaling in brilliancy a, the brightest star of the constellation; but in about two weeks it fell to the ninth magnitude. Huggins and Mil- ler eagerly studied the star with the spectroscope, and their results were received with deepest interest. They concluded that the light of the new star had two different sources, each giving a spectrum peculiar to itself. One of the spectra had dark lines and the other bright lines. It 6 74 PLEASURES OF THE TELESCOPE will be remembered that a similar peculiarity was exhib- ited by the new star in Auriga in 1893. But the star in Corona did not disappear. It diminished to magnitude nine and a half or ten, and stopped 'there; and it is still visible. In fact, subsequent examination proved that it had been catalogued at Bonn as a star of magnitude nine and a half in 1855. Consequently this " blaze star " of 1866 will bear watching in its decrepitude. Nobody knows but that it may blaze again. Perhaps it is a sun- like body; perhaps it bears little resemblance to a sun as we understand such a thing. But whatever it may be, it has proved itself capable of doing very extraordinary things. We have no reason to suspect the sun of any latent eccentricities, like those that have been displayed by "temporary" stars; yet, acting on the principle which led the old emperor-astrologer Rudolph II to torment his mind with self-made horoscopes of evil import, let us un- scientifically imagine that the sun could suddenly burst out with several hundred times its ordinary amount of heat and light, thereby putting us into a proper condition for spectroscopic examination by curious astronomers in distant worlds. But no, after all, it is far pleasanter to keep within the strict boundaries 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 their lanterns over the fields, the stars do not sparkle and blaze like those that pierce the frosty skies of winter. The light of Sirius, Aldebaran, Rigel, and other midwinter brilliants possesses a certain gemlike hardness and cutting quality, but Antares and Vega, the great summer stars, and Arcturus, when he hangs westering in a July night, exhibit a milder radiance, harmonizing with the character of the season. This difference is, of course, atmospheric in origin, although it may be partly subjec- tive, depending upon the mental influences of the muta- tions of Nature. The constellation Scorpio is nearly as striking in out- line as Orion, and its brightest star, the red Antares (a in map No. 12), carries concealed in its rays a green jewel which, to the eye of the enthusiast in telescopic recrea- tion, appears more beautiful and inviting each time that he penetrates to its hiding place. We shall begin our night's work with this object, and the four-inch glass will serve our purpose, although the untrained observer would be more certain of success with 75 76 PLEASURES OF THE TELESCOPE the five-inch. A friend of mine has seen the companion of Antares with a three-inch, but I have never tried the star with so small an aperture. When the air is steady and the companion can be well viewed, there is no finer sight among the double stars. The contrast of colors is beautifully distinct fire-red and bright green. The little green star has been seen emerging from behind the moon, ahead of its ruddy companion. The magnitudes are one and seven and a half or eight, distance 3", p. 270. An- tares is probably a binary, although its binary character has not yet been established. A slight turn of the telescope tube brings us to the star (7, a wide double, the smaller component of which is blue or plum-colored; magnitudes four and nine, distance 20", p. 272. From \ U J^Av 8 >& '@ ^Taruntius MARE TRANQUILITATIS ^ MARE 'luut Caesar ^ VAPOKUM LUNAR CHART No. 1, NORTHWEST QUARTER. range here becomes very narrow. Southeast of this bay lies a conspicuous bright point, the crater mountain Pro- clus, on which the sun has fully risen in the fourth day of the moon, and which reflects the light with extraordinary liveliness. Adjoining Proclus on the east and south is a THE MOUNTAINS AND PLAINS OF THE MOON 159 curious, lozenge-shaped flat, broken with short, low ridges, and possessing a most peculiar light-brown tint, easily dis- tinguished from the general color tone of the lunar land- scapes. It would be interesting to know what was passing in the mind of the old astronomer who named this singular O region Palus Somnii. It is not the only spot on the moon which has been called a " marsh," and to which an unex- plained connection with dreams has been ascribed. Nearly on the same meridian with Proclus, at a distance of about a hundred miles northward, lies a fine example of a ring mountain, rather more than forty miles in diameter, and with peak-tipped walls which in some places are 13,000 feet in height, as measured from the floor within. This is Macrobius. There is an inconspicuous central mountain in the ring. North of the Mare Crisium, and northwest of Macro- bius, we find a much larger mountain ring, oblong in shape and nearly eighty miles in its greatest diameter. It is named Cleomenes. The highest point on its wall is about 10,000 feet above the interior. Near the northeast corner of the wall yawns a huge and very deep crater, Tralles, while at the northern end is another oblong crater mountain called Burckhardt. From Cleomenes northward to the pole, or to the northern extremity of the crescent, if our observations are made during new moon, the ground appears broken with an immense number of ridges, craters, and mountain rings, among which we may telescopically wander at will. One of the more remarkable of these objects, which may be identified with the aid of Lunar 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. Owing to its situation, so far down the side of the lunar globe, it is foreshortened into a long ellipse, although in reality it 160 PLEASURES OF THE TELESCOPE is nearly a circle. A chain of mountains runs north and south across the interior plain. Geminus, Berzelius, and Messala are other rings well worth looking at. The re- markable pair called Atlas and Hercules demand more than passing attention. The former is fifty-five and the lat- ter forty-six miles in diameter. Each sinks 11,000 feet be- low the summit of the loftiest peak on its encircling wall. Both are full of interesting detail sufficient to occupy the careful observer for many nights. The broad ring bearing the name of Endymion is nearly eighty miles in diameter, and has one peak 15,000 feet high. The interior plain is flat and dark. Beyond Endymion on the edge of the disk is part of a gloomy plain called the Mare Humboltianum. After glancing at the crater-shaped mountains on the western and southern border of the Mare Crisium, Alha- zen, Hansen, Condorcet, Firmicus, etc., we pass southward into the area covered in Lunar Chart No. 2. The long dark plain south of the Mare Crisium is the Mare Fecundi- tatiSy though why it should have been supposed to be par- ticularly fecund, or fertile, is by no means clear. On the western border of this plain, about three hundred miles from the southern end of the Mare Crisium, is the mountain ring, or circumvallation, called Langrenus, about ninety miles across and in places 10,000 feet high. There is a fine central mountain with a number of peaks. Nearly a hun- dred miles farther south, on the same meridian, lies an equally extensive mountain ring named Vendelinus. The broken and complicated appearance of its northern walls will command the observer's attention. Another similar step southward, and still on the same meridian brings us to a yet finer mountain ring, slightly larger than the others, and still more complicated in its walls, peaks, and terraces, and in its surroundings of craters, gorges, and broken ridges. This is Petavius. West of Petavius, on the very THE MOUNTAINS AND PLAINS OF THE MOON 161 edge of the disk, is a wonderful formation, a walled plain named Humboldt, which is looked down upon at one point near its eastern edge by a peak 16,000 feet in height. About a hundred and forty miles south of Petavius is the 4&* LUNAK CHART No. 2, SOUTHWEST QUARTER. fourth great mountain ring lying on the same meridian. Its name is Furnerius. Look particularly at the brilliantly shining crater on the northeast slope of the outer wall of Furnerius. 162 PLEASURES OF THE TELESCOPE Suppose that our observations are now interrupted, to be resumed when the moon, about " seven days old," is in its first quarter. If we had time, it would be a most interesting thing to watch the advance of the lunar sun- rise every night, for new beauties are displayed almost from hour to hour; but, for the purposes of our descrip- tion, it is necessary to curtail the observations. At first quarter one half of the lunar hemisphere which faces the earth is illuminated by the sun, and the line of sunrise runs across some of the most wonderful regions of the moon. We begin, referring once more to Lunar Chart No. 1, in the neighborhood of the north pole of the moon. Here the line along which day and night meet is twisted and broken, owing to the roughness of the lunar surface. About fifteen degrees southwest of the pole lies a remark- able square-cornered, mountain-bordered plain, about forty miles in length, called Barrow. Very close to the pole is a ring mountain, about twenty-five miles in diam- eter, whose two loftiest peaks, 8,000 to 9,000 feet high, according to Neison, must, from their situation, enjoy per- petual day. The long, narrow, dark plain, whose nearest edge is about thirty degrees south of the pole, is the Mare Frigoris, bordered on both sides by uplands and mountains. At its southern edge we find the magnificent Aristoteles, a mountain ring, sixty miles across, whose immense wall is composed of terraces and ridges running up to lofty peaks, which rise nearly 11,000 feet above the floor of the val- ley. About a hundred miles south of Aristoteles is Eudox- us, another fine mountain ring, forty miles in diameter, and quite as deep as its northern neighbor. These two make a most striking spectacle. We are now in the neighborhood of the greatest moun- THE MOUNTAINS AND PLAINS OF TEE MOON 163 tain chains on the moon, the lunar Alps lying to the east and the lunar Caucasus to the south of Aristoteles and Eudoxus, while still farther south, separated from the Caucasus by a strait not more than a hundred miles broad, begins the mighty range of the lunar Apennines. We first turn the telescope on the Alps. As the line of sunrise runs directly across their highest peaks, the effect is startling. The greatest elevations are about 12,000 feet. The observer's eye is instantly caught by a great valley, running like a furrow through the center of the mountain mass, and about eighty or ninety miles in length. The sealike expanse south and southeast of the Alps is the Mare Imbrium, and it is along the coast of this so-called sea that the Alps attain their greatest height. The valley, or gorge, above mentioned, appears to cut through the loftiest mountains and to reach the " coast," although it is so narrowed and broken among the greater peaks that its southern portion is almost lost before it actually reaches the Mare Imbrium. Opening wider again as it enters the Mare, it forms a deep bay among precipi- tous mountains. The Caucasus Mountains are not so lofty nor so pre- cipitous as the Alps, and consequently have less attrac- tion for the observer. They border the dark, oval plain of the Mare Serenitatis on its northeastern side. The great bay running out from the Mare toward the northwest, be- tween the Caucasus and the huge mountain ring of Posi- donius, bears the fanciful name of Lacus Somniorum. In the old days when the moon was supposed to be inhabited, those terrestrial godfathers, led by the astronomer Ricci- oli, who were busy bestowing names upon the " seas " and mountains of our patient satellite, may have pleased their imagination by picturing this arm of the " Serene Sea " as a peculiarly romantic sheet of water, amid whose magni- 164 PLEASURES OF THE TELESCOPE cal influences the lunar gentlefolk, drifting softly in their silver galleons and barges, and enjoying the splendors of " full earth " poured upon their delightful little world, were accustomed to fall into charming reveries, as even we hard-headed sons of Adam occasionally do when the waters under the keel are calm and smooth and the balmy air of a moonlit night invokes the twin spirits of poetry and music. Posidonius, the dominating feature of the shore line here, is an extraordinary example of the many formations on the moon which are so different from everything on the earth that astronomers do not find it easy to bestow upon them names that truly describe them. It may be called a ring mountain or a ringed plain, for it is both. Its diameter exceeds sixty miles, and the interior plain lies about 2,000 feet below the outer surface of the lunar ground. The mountain wall surrounding the ring is by no means remarkable for elevation, its greatest height not exceeding 6,000 feet, but, owing to the broad sweep of the curved walls, the brightness of the plain they inclose, and the picturesque irregularity of the silhouette of shadow thrown upon the valley floor by the peaks encir- cling it, the effect produced upon the observer is very striking and attractive. Having finished with Posidonius and glanced across the broken region of the Taurus Mountains toward the west, we turn next to consider the Mare Serenitatis. This broad gray plain, which, with a slight magnifying power, certainly looks enough like a sea to justify the first tele- scopists in thinking that it might contain water, is about 430 by 425 miles in extent, its area being 125,000 square miles. Running directly through its middle, nearly in a north and south line, is a light streak, which even a good opera glass shows. This streak is the largest and most THE MOUNTAINS AND PLAINS OF THE MOON 165 wonderful of the many similar rays which extend on all sides from the great crater, or ring, of Tycho in the south- ern hemisphere. The ray in question is more than 2,000 miles long, and, like its shorter congeners, it turns aside for nothing; neither " sea," nor peak, nor mountain range, nor crater ring, nor gorge, nor caiion, is able to divert it from its course. It ascends all heights and drops into all depths with perfect indifference, but its continuity is not broken. When the sun does not illuminate it at a proper angle, however, the mysterious ray vanishes. Is it a metallic vein, or is it volcanic lava or ash? Was the globe of the moon once split open along this line? The Mare Serenitatis is encircled by mountain ranges to a greater extent than any of the other lunar " seas." On its eastern side the Caucasus and the Apennines shut it in, except for a strait a hundred miles broad, by means of which it is connected with the Mare Imbrium. On the south the range of the Hsemus Mountains borders it, on the north and northwest the Caucasus and the Taurus Mountains confine it, while on the west, where again it connects itself by a narrow strait with another " sea," the Mare TranquiUtatis, it encounters the massive uplift of Mount Argseus. Not far from the eastern strait is found the remarkable little crater named Linne', not con- spicuous on the gray floor of the Mare, yet easily enough found, and very interesting because a considerable change of form seems to have come over this crater some time near the middle of the nineteenth century. In referring to it as a crater it must not be forgotten that it does not form an opening in the top of a mountain. In fact, the so-called craters on the moon, generally speaking, are simply cavities in the lunar surface, whose bottoms lie deep below the general level, instead of being elevated on the summit of mountains, and inclosed in a conical peak. 166 PLEASURES OF THE TELESCOPE In regard to the alleged change in Linne, it has been sug- gested, not that a volcanic eruption brought it about, but that a downfall of steep walls, or of an unsupported rocky floor, was the cause. The possibility of such an occur- rence, it must be admitted, adds to the interest of the ob- server who regularly studies the moon with a telescope. Just on the southern border of the Mare, the beautiful ring Menelaus lies in the center of the chain of the Hsemus Mountains. The ring is about twenty miles across, and its central peak is composed of some highly reflecting material, so that it shines very bright. The streak or ray from Tycho which crosses the Mare Serenitatis passes through the walls of Menelaus, and perhaps the central peak is composed of the same substance that forms the ray. Something more than a hundred miles east-southeast from Menelaus, in the midst of the dark Mare Vaporum, is another brilliant ring mountain which catches the eye, Manilius. It exceeds Menelaus in brightness as well as in size, its diameter being about twenty-five miles. There is something singular underlying the dark lunar surface here, for not only is Manilius extraordinarily brilliant in contrast with the surrounding plain, but out of that plain, about forty miles toward the east, projects a small moun- tain which is also remarkable for its reflecting properties, as if the gray ground were underlain by a stratum of some material that flashes back the sunlight wherever it is ex- posed. The crater mountain, Sulpicius Gallus, on the bor- der of the Mare, north of Manilius and east of Menelaus, is another example of the strange shining quality of certain formations on the moon. Follow next the Ha3mus range westward until the at- tention falls upon the great ring mountain Plinius, more than thirty miles across, and bearing an unusual resem- blance to a fortification. Mr. T. G. Elger, the celebrated THE MOUNTAINS AND PLAINS OF THE MOON 167 English selenographer, says of Plinius that, at sunrise, " it reminds one of a great fortress or redoubt erected to command the passage between the Mare Tranquilitatis and the Mare Serenitatis." But, of course, the resemblance is purely fanciful. Men, even though they dwelt in the moon, would not build a rampart 6,000 feet high! Mount Argseus, at the southwest corner of the Mare Serenitatis, is a very wonderful object when the sun has just risen upon it. This occurs five days after the new moon. Keturning to the eastern extremity of the Mare, we glance, in passing, at the precipitous Mount Hadley, which rises more than 15,000 feet above the level of the Mare and forms the northern point of the Apennine range. Passing into the region of the Mare Imbrium, whose western end is divided into the Palus Putredinis on the south and the Palus Nebularum on the north, we notice three conspicu- ous ring mountains, Cassini near the Alps, and Aristillus and Autolycus, a beautiful pair, nearly opposite the strait connecting the two Maria. Cassini is thirty-six miles in diameter, Aristillus thirty-four, and Autolycus twenty-three. The first named is shallow, only 4,000 feet in depth from the highest point of its wall, while Aristil- lus carries some peaks on its girdle 11,000 feet high. Au- tolycus, like Cassini, is of no very great depth. Westward from the middle of an imaginary line joining Aristillus and Cassini is the much smaller crater Thesete- tus. Outside the walls of this are a number of craterlets, and a French astronomer, Charbonneaux, of the Meudon Observatory, reported in December, 1900, that he had re- peatedly observed white clouds appearing and disappear- ing over one of these small craters. South of the Mare Vaporum are found some of the most notable of those strange lunar features that are called 168 PLEASURES OF THE TELESCOPE "clefts " or " rills." Two crater mountains, in particular, are connected with them, Ariadseus at the eastern edge of the Mare Tranquilitatis and Hyginus on the southern bor- der of the Mare Vaporum. These clefts appear to be broad and deep chasms, like the caiions cut by terrestrial rivers, but it can not be believed that the lunar canons are the work of rivers. They are rather cracks in the lunar crust, although their bottoms are frequently visible. The prin- cipal cleft from Ariadseus runs eastward and passes be- tween two neighboring craters, the southern of which is named Silberschlag, and is noteworthy for its brightness. The Hyginus cleft is broader and runs directly through the crater ring of that name. The observer will find much to interest him in the great, irregular, and much-broken mountain ring called Julius Caesar, as well as in the ring mountains, Godin, Agrippa, and Triesnecker. The last named, besides pre- senting magnificent shadows when the sunlight falls aslant upon it, is the center of a complicated system of rills, some of which can be traced with our five-inch glass. We next take up Lunar Chart No. 2, and pay a tele- scopic visit to the southwestern quarter of the lunar world. The Mare Tranquilitatis merges through straits into two southern extensions, the More Fecunditatis and the Mare Ncctaris. The great ring mountains or ringed plains, Langrenus, Vendelinus, Petavius, and Furnerius, all lying significantly along the same lunar meridian, have already been noticed. Their linear arrangement and iso- lated position recall the row of huge volcanic peaks that runs parallel with the shore of the Pacific Ocean in Oregon and Washington Mount Jefferson, Mount Hood, Mount St. Helen's, Mount Tacoma but these terrestrial volca- noes, except in elevation, are mere pins' heads in the com- parison. THE MOUNTAINS AND PLAINS OF THE MOON 169 In the eastern part of the Mare Fecunditatis lies a pair of relatively small craters named Messier, which possess particular interest because it has been suspected, though not proved, that a change of form has occurred in one or other of the pair. Madler, in the first half of the nine- teenth century, represented the two craters as exactly alike in all respects. In 1855 Webb discovered that they are not alike in shape, and that the easternmost one is the larger, and every observer easily sees that Webb's descrip- tion is correct. Messier is also remarkable for the light streak, often said to resemble a comet's tail, which ex- tends from the larger crater eastward to the shore of the Mare Fecunditatis. Goclenius and Guttemberg, on the highland between the Mare Fecunditatis and the Mare Nectaris, are intersected and surrounded by clefts, besides being remarkable for their broken and irregular though lofty walls. Guttem- berg is forty-five miles and Goclenius twenty-eight miles in diameter. The short mountain range just east of Gut- temberg, and bordering a part of the Mare Nectaris on the west, is called the Pyrenees. The Mare Nectaris, though offering in its appearance no explanation of its toothsome name perhaps it was re- garded as the drinking cup of the Olympian gods is one of the most singular of the dark lunar plains in its out- lines. At the south it ends in a vast semicircular bay, sixty miles across, which is evidently a half-submerged mountain ring. But submerged by what? Not water, but perhaps a sea of lava which has now solidified and forms the floor of the M are Nectaris. The name of this sin- gular formation is Fracastorius. Elger has an interest- ing remark about it. " On the higher portion of the interior, near the cen- ter," he says, " is a curious object consisting apparently of 13 170 PLEASURES OF THE TELESCOPE four light spots, arranged in a square, with a craterlet in the middle, all of which undergo notable changes of aspect under different phases." Other writers also call attention to the fine markings, minute craterlets, and apparently changeable spots on the floor of Fracastorius. We go now to the eastern side of the Mare Nectaris, where we find one of the most stupendous formations in the lunar world, the great mountain ring of Theophilus, noticeably regular in outline and perfect in the complete- ness of its lofty wall. The circular interior, which con- tains in the center a group of mountains, one of whose peaks is 6,000 feet high, sinks 10,000 feet below the gen- eral level of the moon outside the wall! One of the peaks on the western edge towers more than 18,000 feet above the floor within, while several other peaks attain eleva- tions of 15,000 to 16,000 feet. The diameter of the immense ring, from crest to crest of the wall, is sixty-four miles. Theophilus is especially wonderful on the fifth and sixth days of the moon, when the sun climbs its shining pinna- cles and slowly discloses the tremendous chasm that lies within its circles of terrible precipices. On the southeast Theophilus is connected by exten- sions of its walls with a shattered ring of vast extent called Cyrillus; and south from Cyrillus, and connected with the same system of broken walls, lies the still larger ring named Catharina, whose half-ruined walls and numer- ous crater pits present a fascinating spectacle as the shadows retreat before 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 most riotous imagination. South of the Mare Nectaris the huge ring mountain of THE MOUNTAINS AND PLAINS OF THE MOON 171 Piccolomini attracts attention, its massive walls sur- rounding a floor nearly sixty miles across, and rising in some places to an altitude of nearly 15,000 feet. It should be understood that wherever the height of the mountain wall of such a ring is mentioned, the refer- ence level is that of the interior plain or floor. The elevation, reckoned from the outer side, is always very much less. The entire region south and east of Theophilus and its great neighbors is marvelously rough and broken. Ap- proaching the center of the moon, we find a system of ringed plains even greater in area than any of those we have yet seen. Hipparchus is nearly a hundred miles long from north to south, and nearly ninety miles broad from east to west. But its walls have been destroyed to such an extent that, after all, it yields in grandeur to a formation like Theophilus. Albategnius is sixty-five miles across, with peaks from 10,000 to 15,000 feet in height. Sacrobosco is a confused mass of broken and distorted walls. Aliacensis is re- markable for having a peak on the eastern side of its wall which is more than 16,000 feet high. Werner, forty-five miles in diameter, is interesting because under its north- eastern wall Miidler, some seventy years ago, saw a light spot of astonishing brightness, unmatched in that respect by anything on the moon except the peak of Aristarchus, which we shall see later. This spot seems afterward to have lost brilliance, and the startling suggestion has been made that its original brightness might have been due to its then recent deposit from a little crater that lies in the midst of it. Walter is of gigantic dimensions, about one hundred miles in diameter. Unlike the majority of the ringed plains, it departs widely from a circle. Stofler is yet larger than Walter; but most interesting of all these 172 PLEASURES OF THE TELESCOPE gigantic formations is Maurolycus, whose diameter ex- ceeds one hundred and fifty miles, and which has walls 13,000 or 14,000 feet high. Yet, astonishing though it may seem, this vast and complicated mass of mountain walls, craters, and peaks, is virtually unseen at full moon, owing to the perpendicularity of the sunlight, which pre- vents the casting of shadows. We shall next suppose that another period of about seven days has elapsed, the moon in the meantime reach- ing its full phase. We refer for guidance to Lunar Chart No. 3. The peculiarity of the northeastern quadrant which immediately strikes the eye is the prevalence of the broad plains called if aria, or " seas." The northern and central parts are occupied by the Mare Imbrium, the " Sea of Showers " or of " Rains," with its darljp bay the Sinus Mstuum, while the eastern half is covered by the vast Oceanus Procellarum, the " Ocean of Storms " or of " Tem- pests." Toward the north a conspicuous oval, remarkably dark in hue, immediately attracts our attention. It is the cele- brated 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 a favor- ite subject for study by selenographers because of the changes of color which its broad, flat floor undergoes as the sun rises upon it, and also because of the existence of enigmatical spots and streaks whose visibility changes. South of Plato, in the Mare Imbrium, rises a precipitous, isolated peak called Pico, 8,000 feet in height. Its resem- blance in situation to the conical mountain Pico in the Azores strikes the observer. 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 Rain- THE MOUNTAINS AND PLAINS OF THE MOON 173 bows." The northwestern extremity of this remarkable bay is guarded by a steep and lofty promontory called Cape Laplace, while the southeastern extremity also has its towering guardian, Cape Heraclides. The latter is MBDII <$Gambart Encke 9 W (, \ / . \\Kepter \ f V Bevel ( , .SINUS S-TUUM Galileo Uhi * ? ' f/ i'/ / LUNAR CHART No. 3, NORTHEAST QUARTER. interesting for showing, between nine and ten days after full moon, a singularly perfect profile of a woman's face looking out across the Mare Tmbrium. The winding lines, like submerged ridges, delicately marking the floor of the Sinus Iridum and that of the Mare beyond, are beautiful 174 PLEASURES OF THE TELESCOPE telescopic objects. The " bay " is about one hundred and thirty-five miles long by eighty-four broad. The Mare Imlrium, covering 340,000 square miles, is sparingly dotted over with craters. All of the more con- spicuous of them are indicated in the chart. The smaller ones, like Caroline Herschel, Helicon, Leverrier, Delisle, etc, vary from eight to twelve miles in diameter. Lam- bert is seventeen miles in diameter, and Euler nineteen, while Timocharis is twenty-three miles broad and 7,000 feet deep below its walls, which rise only 3,000 feet above the surface of the Mare. Toward the eastern border of the sea, south of the Har- binger Mountains, we find a most remarkable object, the mountain ring, or crater plain, called Aristarchus. This ring is not quite thirty miles in diameter, but there is nothing on the moon that can compare with it in dazzling brilliance. The central peak, 1,200 or 1,300 feet high, gleams like a mountain of crusted snow, or as if it were composed of a mass of fresh-broken white metal, or of com- pacted crystals. Part of the inner slope of the east wall is equally brilliant. In fact, so much light is poured out of the circumvallation that the eye is partially blinded, and unable distinctly to see the details of the interior. No satisfactory explanation of the extraordinary reflecting power of Aristarchus has ever been offered. Its neighbor toward the east, Herodotus, is somewhat smaller and not remarkably bright, but it derives great interest from the 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 floor of the Mare, making an abrupt turn when it reaches the foot of the Harbinger Mountains. The comparatively small crater, Lichtenberg, near the northeastern limb of the moon, is interesting because Mad- THE MOUNTAINS AND PLAINS OF THE MOON 175 ler used to see in its neighborhood a pale-red tint which has not been noticed since his day. Returning to the western side of the quadrant repre- sented in Lunar Chart No. 3, we see the broad and beauti- fully regular ringed plain of Archimedes, fifty miles in diameter and 4,000 feet deep. A number of clefts extend between the mountainous neighborhood of Archimedes and the feet of the gigantic Apennine Mountains on the southwest. The little double crater, Beer, between Archimedes and Timocharis, is very bright. The Apennines extend about four hundred and eighty miles in a northwesterly and southeasterly direction. One of their peaks near the southern end of the range, Mount Huygens, is at least 18,000 feet high, and the black silhouettes of their sharp-pointed shadows thrown upon the smooth floor of the Mare Imbrium about the time of first quarter present a spectacle as beautiful as it is unique. The Apennines end at the southeast in the ring mountain, Eratosthenes, thirty-eight miles across and very deep, one of its encircling chain of peaks rising 16,000 feet above the floor, and about half that height above the level of the Mare Imbrium. The shadows cast by Eratosthenes at sunrise ar magnificent. And now we come to one of the supreme spectacles of the moon, the immense ring or crater mountain Coperni- cus. This is generally regarded as the grandest object that the telescope reveals on the earth's satellite. It is about fifty-six miles across, and its interior falls to a depth of 8,000 feet below the Mare Imbrium. Its broad wall, composed of circle within circle of ridges, terraces, and precipices, rises on the east about 12,000 feet above the floor. On the inner side the slopes are very steep, cliff falling below cliff, until the bottom of the fearful abyss is 176 PLEASURES OF THE TELESCOPE attained. To descend th'ose precipices and reach the de- pressed floor of Copernicus would be a memorable feat for a mountaineer. In the center of the floor rises a compli- cated mountain mass about 2,400 'feet high. All around Copernicus the surface of the moon is dotted with count- less little crater pits, and splashed with whitish streaks. Northward lie the Carpathian Mountains, terminating on the 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 of whitish streaks and splashes, is twenty-two miles in diameter, and notably brilliant. Finally, we turn to the southeastern quadrant of the moon, represented in Lunar Chart No. 4. The broad, dark expanse extending from the north is the Mare Nubium on the west and the Oceanus Procellarum on the east. To- ward the southeast appears the notably dark, rounded area of the Mare Humorum inclosed by highlands and rings. We begin with the range of vast inclosures run- ning southward near the central meridian, and starting with Ptolemseus, a walled plain one hundred and fifteen miles in its greatest diameter and covering an area con- siderably exceeding that of the State of Massachusetts. Its neighbor toward the south, Alphonsus, is eighty-three miles across. Next comes Arzachel, more than sixty-five miles 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, forming the buttresses of a low mountain. Purbach is sixty miles broad, and south of that comes a wonderful region where the ring mountains Hell, Ball, Lexell, and others, more or less connected with walls, inclose an area even larger than THE MOUNTAINS AND PLAINS OF THE MOON 177 Ptolemseus, but which, not being so distinctly bordered as some of the other inclosed plains, bears no distinctive name. The next conspicuous object toward the south ranks with Copernicus among the grandest of all lunar phe- $0g&#wfofl_.^ \\Sr-," ^3vW/JVy// J 4S ^" -7V ' ^fetfte^ ijiqrii/iije _ Viet a r^s*-^^' N ^^* ytomontaniis MARE ^S HUMORUM ^ . BulUaMus ^ M EMv>ta(^ \^' N&llet ''Q ; AyatharchMes to '^'/^ ^J^rz^-A^/ ra^lT^IM^ NUBJUM ^m Lassell Parry?: -' Damoiseau Flamsteed iQ ^Landsbetyj LUNAR CHART No. 4, SOUTHEAST QUARTER. nomena the ring, or crater, Tycho. It is about fifty-four miles in diameter and some points on its wall rise 17,000 feet above the interior. In the center is a bright moun- 178 PLEASURES OF THE TELESCOPE tain peak 5,000 feet high. But wonderful as are the de- tails of its mountain ring, the chief attraction of Tycho is its manifest relation to the, mysterious bright rays hereto- fore referred to, which extend far across the surface of the moon in all directions, and of which it is the center. The streaks about Copernicus are short and confused, con- stituting rather a splash than a regular system of rays; but those emanating from Tycho are very long, regular, comparatively narrow, and form arcs of great circles which stretch away for hundreds of miles, allowing no obstacle to interrupt their course. Southwest of Tycho lies the vast ringed plain of Ma- ginus, a hundred miles broad and very wonderful to look upon, with its labyrinth of formations, when the sun slopes across it, and yet, like Maurolycus, invisible under a vertical illumination. " The full moon," to use Mad- ler's picturesque expression, " knows no Maginus." Still larger and yet more splendid is Clavius, which exceeds .one hundred and forty miles in diameter and covers 16,000 square miles of ground within its fringing walls, which carry some of the loftiest peaks on the moon, several at- taining 17,000 feet. The floor is deeply depressed, so that an inhabitant of this singular inclosure, larger than Massa- chusetts, Connecticut, and Rhode Island combined, would dwell in land sunk two miles below the general level of the world about him. In the neighborhood of the south pole lies the large walled plain of Newton, whose interior is the deepest known depression on the moon. It is so deep that the sun- shine never touches the larger part of the floor of the inner abyss, and a peak on its eastern wall rises 24,000 feet sheer above the tremendous pit. Other enormous walled plains are Longomontanus, Wilhelm I, Schiller, Bailly, and Schickard. The latter is one hundred and THE MOUNTAINS AND PLAINS OF THE MOON 179 thirty-four miles long and bordered by a ring varying from 4,000 to 9,000 feet in height. Wargentin, the oval close to the moon's southeast limb, beyond Schickard, is a unique formation in that, instead of its interior being sunk be- low the general level, it is elevated above it. It has been suggested that this peculiarity is due to the 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 dome arched 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 huge yawning crater on its eastern wall; Capu- anus for a brilliant shining crater also on its eastern wall; and Mercator for possessing bright craters on both its east and its west walls. Vitello has a bright central mountain and gains conspicuousness from its position at the edge of the dark Mare Humorum. Agatharchides is the broken remnant of a great ring mountain. Gassendi, an extremely beautiful object, is about fifty-five miles across. It is encircled with broken walls, craters and and bright points, and altogether presents a 'very splen- did appearance about the eleventh day of the moon's age. Letronne is a half-submerged ring, at the southern end of the Oceanus Procellarum, which recalls Fracastorius in the western lunar hemisphere. It lies, however, ten de- grees nearer the equator than Fracastorius. Billy is a mountain ring whose interior seems to have been sub- merged by the dark substance of the Oceanus Procellarum, although its walls have remained intact. Mersenius is a very conspicuous ring, forty miles in diameter, east of the Mare Humorum. Vieta, fifty miles across, is also a fine object. Grimaldi, a huge dusky oval, is nearly one hun- dred and fifty miles in its greatest length. The ring moun- 180 PLEASURES OF THE TELESCOPE tain Landsberg, on the equator, and near the center of the visible eastern hemisphere, is worth watching because Elger noticed changes of color in its interior in 1888. Bullialdus, in the midst of the Mare Nubium, is a very conspicuous and beautiful ring mountain about thirty- eight miles in diameter, with walls 8,000 feet high above the interior. Those who wish to see the lunar mountains in all their varying aspects will not content themselves with views obtained during the advance of the sunlight from west to east, between " new moon " and " full moon," but will con- tinue their observations during the retreat of the sunlight from east to west, after the full phase is passed. It is evident that the hemisphere of the moon which is forever turned away from the earth is quite as marvelous in its features as the part that we see. It will be noticed that the entire circle of the moon's limb, with insignificant interruptions, is mountainous. Possibly the invisible side of our satellite contains yet grander peaks and crater mountains than any that our telescopes can reach. This probability is increased by the fact that the loftiest known mountain on the moon is neyer seen except in sil- houette. It is a member of a great chain that breaks the lunar limb west of the south pole, and that is called the Leibnitz Mountains. The particular peak referred to is said by some authorities to exceed 30,000 feet in height. Other great ranges seen only in profile are the Dorfel Mountains on the limb behind the ring plain Bailly, the Cordilleras, east of Eichstadt, and the D'Alembert Moun- tains beyond Grimaldi. The profile of these great moun- tains is particularly 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 startling distinctness. TEE SPECTACLES OF THE SUN 181 THE SUN When the sun is covered with spots it becomes a most interesting object for telescopic study. Every amateur's telescope should be provided with apparatus for viewing the sun. A dark shade glass is not sufficient and not safe. What is known as a solar prism, consisting of two solid prisms of glass, cemented together in a brass box which carries a short tube for the eyepiece, and reflecting an im- age of the sun from their plane of junction while the major remnant of light and heat passes directly through them and escapes from an opening provided for the pur- pose serves very well. Better and more costly is an ap- paratus called a helioscope, constructed on the principle of polarization and provided with prisms and reflectors which enable the observer, by proper adjustment, to gov- ern very exactly and delicately the amount of light that passes into the eyepiece. Furnished with an apparatus of this description we can employ either a three-, four-, or five-inch glass upon the sun with much satisfaction. For the amateur's purposes the sun is only specially interesting when it is spotted. The first years of the twentieth century will behold a gradual growth in the number and size of the solar spots as those years happen to coincide with the increasing phase of the sun-spot period. Large sun spots and groups of spots often present an immense amount of detail which tasks the skill of the draughtsman to represent it. But a little practice will enable one to produce very good repre- sentations of sun spots, as well as of the whitish patches called faculse by which they are frequently surrounded. For the simple purpose of exhibiting the spotted face of the sun without much magnifying power, a telescope may be used to project the solar image on a white sheet or 182 PLEASURES OF THE TELESCOPE screen. If the experiment is tried in a room, a little in- genuity will enable the observer to arrange a curtain cov- ering the window used, in such a way as to exclude all the light except that which comes" through the telescope. Then, by placing a sheet of paper or a drawing board be- fore the eyepiece and focusing the image of the sun upon it, very good results may be obtained. If one has a permanent mounting and a driving clock, a small spectroscope may be attached, for solar observa- tions, even to a telescope of only four or five inches aper- ture, and with its aid most interesting views may be ob- tained of the wonderful red hydrogen flames that fre- quently appear at the edge of the solar disk. CHAPTER X ARE THERE PLANETS AMONG THE STARS? "... And if there should be Worlds greater than thine own, inhabited By greater things, and they themselves far more In number than the dust of thy dull earth, What wouldst thou think ? " BYRON'S CAIN. THIS always interesting question has lately been re- vived in a startling manner by discoveries that have seemed to reach almost deep enough to touch its solution. The following sentences, from the pen of Dr. T. J. J. See, of the Lowell Observatory, are very significant from this point of view: " Our observations during 1896- ? 97 have certainly dis- closed stars more difficult than any which astronomers had seen before. Among these obscure objects about half a dozen are truly wonderful, in that they seem to be dark, almost black in color, and apparently are shining by a dull reflected light. It is unlikely that they will prove to be self-luminous. If they should turn out dark bodies in fact, shining only by the reflected light of the stars around which they revolve, we should have the first case of planets dark bodies noticed among the fixed stars." Of course, Dr. See has no reference in this state- ment to the immense dark bodies which, in recent years, have been discovered by spectroscopic methods revolving around some of the visible stars, although invisible them- selves. The obscure objects that he describes belong to a different class, and might be likened, except perhaps 183 184 PLEASURES OF THE TELESCOPE in magnitude, to the companion of Sirius, which, though a light-giving body, exhibits nevertheless a singular defect of luminosity in relation to its mass. Sirius has only twice the mass, but ten thousand-times the luminosity, of its strange companion! Yet the latter is evidently rather a faint, or partially extinguished, sun than an opaque body shining only with light borrowed from its dazzling neighbor. The objects seen by Dr. See, on the contrary, are " apparently shining by a dull reflected light." If, however (as he evidently thinks is probable), these objects should prove to be really non-luminous, it would not follow that they are to be regarded as more like the planets of the solar system than like the dark companions of certain other stars. A planet, in the sense which we attach to the word, can not be comparable in mass and size with the sun around which it revolves. The sun is a thousand times larger than the greatest of its attendant planets, Jupiter, and more than a million times larger than the earth. It is extremely doubtful whether the re- lation of sun and planet could exist between two bodies of anything like equal size, or even if one exceeded the other many times in magnitude. It is only when the dif- ference is so great that the smaller of the two bodies is insignificant in comparison with the larger, that the for- mer could become a cool, life-bearing globe, nourished by the beneficent rays of its organic comrade and master. Judged by our terrestrial experience, which is all we have to go by, the magnitude of a planet, if it is to bear life resembling that of the earth, is limited by other con- siderations. Even Jupiter, which, as far as our knowl- edge extends, represents the extreme limit of great plan- etary size, may be too large ever to become the abode of living beings of a high organization. The force of gravi- tation on the surface of Jupiter exceeds that on the ARE THERE PLANETS AMONG THE STARS? 185 earth's surface as 2.64 to 1. Considering the effects of this on the weight and motion of bodies, the density of the atmosphere, etc., it is evident that Jupiter would, to say the very least, be an exceedingly uncomfortable place of abode for beings resembling ourselves. But Jupiter, if it is ever to become a solid, rocky globe like ours, must shrink enormously in volume, since its density is only 0.24 as compared with the earth. Now, the surface gravity of a planet depends on its mass and its radius, being directly as the former and inversely as the square of the latter. But in shrinking Jupiter will lose none of its mass, al- though its radius will become much smaller. The force of gravity will consequently increase on its surface as the planet gets smaller and more dense. The present mean diameter of Jupiter is 86,500 miles, while its mass exceeds that of the earth in the ratio of 316 to 1. Suppose Jupiter shrunk to three quarters of its present diameter, or 64,800 miles, then its surface gravity would exceed the earth's nearly five times. With one half its present diameter the surface gravity would become more than ten times that of the earth. On such a planet a man's bones would snap beneath his weight, even grant- ing that he could remain upright at all! It would seem, then, that, unless we are to abandon terrestrial analogies altogether and " go it blind," we must set an upper limit to the magnitude of a habitable planet, and that Jupiter represents such upper limit, if, indeed, he does not tran- scend it. The question then becomes, Can the faint objects seen by Dr. See and his fellow-observers, in the near neighbor- hood of certain stars, be planets in the sense just de- scribed, or are they necessarily far greater in magnitude than the largest planet, in the accepted sense of that word, which can be admitted into the category viz., the planet 13 186 PLEASURES OF THE TELESCOPE Jupiter? This resolves itself into another question: At what distance would Jupiter be visible with a powerful telescope, supposing it to receive from a neighboring star an amount of illumination not les than that which it gets from the sun? To be sure, we do not know how far away the faint objects described by Dr. See are; but, at any rate, we can safely assume that they are at the distance of the nearest stars, say somewhere about three hundred thousand times the earth's distance from the sun. The sun itself removed to that distance would appear to our only as a star of the first magnitude. But Zollner shown that the sun exceeds Jupiter 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 the ratio of their light if both sun and Jupiter could be removed to about the distance of the nearest stars. Since the sun would then be only as bright as one of the stars of the first magnitude, and since Jupiter would be 218,000,000 times less brilliant, it is evident that the latter would not be visible at all. The faintest stars that the most powerful telescopes are able to show probably do not fall below the sixteenth or, at the most, the seven- teenth magnitude. But a seventeenth-magnitude star i& only between two and three million times fainter than the sun would appear at the distance above supposed, while, as we have seen, Jupiter would 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 faintest star which the largest telescope is just able, under the most exquisite conditions, to glimpse. To see a star so faint as that would require an object-glass of a diameter half as great as the length of the tube of the Lick telescope, or say thirty feet! ARE THERE PLANETS AMONG THE STARS f 187 Of course, Jupiter might be more brilliantly illumi- nated by a brighter star than the sun; but, granting that, it still would not be visible at such a distance, even if we neglect the well-known concealing or blinding effect of the rays of a bright star when the observer is trying to view a faint one close to it. Clearly, then, the obscure objects seen by Dr. See near some of the stars, if they really are bodies visible only by light reflected from their surfaces, must be enormously larger than the planet Jupiter, and can not, accordingly, be admitted into the category of planets proper, whatever else they may be. Perhaps they are extreme cases of what we see in the system of Sirius i. e., a brilliant star with a companion which has ceased to shine as a star while retaining its bulk. Such bodies may be called planets in that they only shine by reflected light, and that they are attached to a brilliant sun; but the part that they play in their systems is not strictly planetary. Owing to their great mass they bear such sway over their shining companions as none of our planets, nor all of 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, must always be the capital feature of a planet, rendering it in the highest degree interesting wherever it may be found- sentient life. It does not follow, however, that there are no real planetary bodies revolving around the stars. As Dr. See himself remarks, such insignificant bodies as our planets could not be seen at the distance of the fixed stars, " even if the power of our telescopes were increased a hundred- fold, and consequently no such systems are known." This brings me to another branch of the subject. In the same article from which I have already quoted (Recent Discoveries respecting the Origin of the Universe, Atlantic 188 PLEASURES OF THE TELESCOPE Monthly, vol. Ixxx, pages 484-492), Dr. See sets forth the main results of his well-known studies on the origin of the double and multiple star systems. He finds that the stel- lar 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 fre- quently equal and always comparable in mass, whereas our satellites are insignificant compared to their plan- ets, and the planets are equally small compared to the sun." These peculiarities of the star systems Dr. See ascribes to the effect of " tidal friction," the double stars having had their birth through fission of original fluid masses (just as the moon, according to George Darwin's theory, was born from the earth), and the reaction of tidal fric- tion having not only driven them gradually farther apart but rendered their orbits more and more eccentric. This manner of evolution of a stellar system Dr. See contrasts with Laplace's hypothesis of the origin of the planetary system through the successive separation of rings from the periphery of the contracting solar nebula, and the gradual breaking up of those rings and their aggregation into spherical masses or planets. While not denying that the process imagined by Laplace may have taken place in our system, he discovers no evidence of its occurrence among the double stars, and this leads him to the follow- ing statement, in which believers in the old theological doctrine that the earth is the sole center of mortal life and of divine care would have found much comfort: " It is very singular that no visible system yet dis- cerned has any resemblance to the orderly and beautiful ARE THERE PLANETS AMONG THE STARS? 189 system in which we live; and one is thus led to think that probably our system is unique in its character. At least it is unique among all known systems." If we grant that the solar system is the only one in which small planets exist revolving around their sun in nearly circular orbits, then indeed we seem to have closed all the outer universe against such beings as the inhabit- ants of the earth. Beyond the sun's domain only whirling stars, coupled in eccentric orbits, dark stars, some of them, but no planets in short a wilderness, full of all energies except those of sentient life! This is not a pleasing pic- ture, and I do not think we are driven to contemplate it. Beyond doubt, Dr. See is right in concluding that double and multiple star systems, with their components all of magnitudes comparable among themselves, revolving in exceedingly eccentric orbits under the stress of mutual gravitation, bear no resemblance to the orderly system of our sun with its attendant worlds. And it is not easy to imagine that the respective members of such systems could themselves be the centers of minor systems of planets, on account of the perturbing influences to which the orbits of such minor systems would be subjected. But the double and multiple stars, numerous though they be, are outnumbered a hundred to one by the single stars which shine alone as our sun does. What reason can we have, then, for excluding these single stars, consti- tuting as they do the vast majority of the celestial host, from a similarity to the sun in respect to the manner of their evolution from the original nebulous condition? These stars exhibit no companions, such planetary at- tendants as they may have lying, on account of their minuteness, far beyond the reach of our most powerful in- struments. But since they vastly outnumber the binary and multiple systems, and since they resemble the sun in 190 PLEASURES OF TEE TELESCOPE having no large attendants, should we be justified, after all, in regarding our system as " unique "? It is true we do not know, by visual evidence, that the single stars have planets, but we find planets attending the only representa- tive of that class of stars that we are able .to approach closely the sun and we know that the existence of those planets is no mere accident, but the result of the operation of physical laws which must hold good in every instance of nebular condensation. Two different methods are presented in which a rotat- ing and contracting nebula may shape itself into a stellar or planetary system. The first is that described by La- place, and generally accepted as the probable manner of origin of the solar system viz., the separation of rings from the condensing mass, and the subsequent transfor- mation of the rings into planets. The planet Saturn is frequently referred to as an instance of the operation of this law, in which the evolution has been arrested after the separation of the rings, the latter having retained the ring form instead of breaking and collecting into globes, forming in this case rings of meteorites, and reminding us of the comparatively scattered rings of asteroids sur- rounding the sun between the orbits of Mars and Jupiter. This Laplacean process Dr. See regards as theoretically possible, but apparently he thinks that if it took place it was confined to our system. The other method is that of the separation of the original rotating mass into two nearly equal parts. The mechanical possibility of such a process has been proved, mathematically, by Poincare' and Darwin. This, Dr. See thinks, is the method which has prevailed among the stars, and prevailed to such a degree as to make the solar system, formed by the ring method, probably a unique phenomenon in the universe. ARE THERE PLANETS AMONG TEE STARS? 191 Is it not more probable that both methods have been in operation, and that, in fact, the ring method has oper- ated more frequently than the other? If not, why do the single stars so enormously outnumber the double ones? It is of the essence of the fission process that the resulting masses should be comparable in size. If, then, that pro- cess has prevailed in the stellar universe to the practical exclusion of the other, there should be very few single stars; whereas, as a matter of fact, the immense majority of the stars are single. And, remembering that the sun viewed from stellar distances would appear unattended by subsidiary bodies, are we not justified in concluding that its origin is a type of the origin of the other single stars? While it is, as I have remarked, of the essence of the fission process that the resulting parts of the divided mass should be comparable in magnitude, it is equally of the essence of the ring, or Laplacean process, that the bodies separated from the original mass should be comparatively insignificant in magnitude. As to the coexistence of the two processes, we have, perhaps, an example in the solar system itself. Darwin's demonstration of the possible birth of the moon from the earth, through fission and tidal friction, does not apply to the satellites attending the other planets. The moon is relatively a large body, comparable in that respect with the earth, while the satellites of Jupiter and Saturn, for instance, are relatively small. But in the case of Saturn there is visible evidence that the ring process of satellite formation has prevailed. The existing rings have not broken up, but their very existence is a testimony of the origin of the 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 instances illustrating both 192 PLEASURES OF THE TELESCOPE the methods of nebular evolution that we have been deal- ing with. The conclusion, then, seems to be that we are not justi- fied in assuming that the solar system is unique simply because it differs widely from the double and multiple star systems; and that we should rather regard it as probable that the vast multitude of stars which do not appear, when viewed with the telescope, or studied by spectroscopic methods, to have any attendants compara- ble with themselves in magnitude, have originated in a manner resembling that of the sun's origin, and may be the centers of true planetary systems like ours. The argument, I think, goes further than to show the mere possibility of the existence of such planetary systems sur- rounding the single stars. If those stars did not origi- nate in a manner quite unlike the origin of the sun, then the existence of planets in their neighborhood is almost a foregone conclusion, for the sun could hardly have passed through the process of formation out of a rotating nebula without evolving planets during its contraction. And so, notwithstanding the eccentricities of the double stars, we may still cherish the belief that there are eyes to see and minds to think out in celestial space. INDEX NOTE. Double, triple, multiple, and colored stars, star clusters, nebulae, and temporary stars will be found arranged under the heads of their respective constellations. ANDROMEDA, Map No. 24, 125. Stars : o, 126. 7, 128. /t, 126. 36, 128. Temporary star : 1885, 127. Cluster : 457, 128. Variable : R, 128. Nebula : 116, 126. AQUARIUS, Map No. 18, 107. Stars : 106. T, 108. *, 108. 41, 106. 2 2729, 106. 2 2745 (12), 106. 2 2998, 108. Variables: R, 108. S, 108. T, 106. Nebute : 4628 (Rosse's " Saturn "), 108. 4678, 108. AQUILA, Map No. 16, 95. Stars : , 94. 11, 94. 23, 94. 57, 94. 2 2644, 94. 2 2544, 94. Cluster : 4440, 94. Variables : 17, 94. R, 94. ARGO : Map No. 2, 31 ; Map No. 7, 55. Stars : 2 1097, 33. 2 1146 (5), 35. Clusters : 1551, 35. Clusters : 1564, 35. 1571, 35. 1630, 56. Nebula : 1564, 35. ARIES, Map No. 22, 119. Stars : 7, 118. , 120. X, 118. IT, 118. 14, 118. 30, 118. 41, 118. 52, 120. 2 289, 118. AURIGA, Map No. 5, 45. Stars : a (Capella), 44. (Menkalina), 46. e, 50. 0, 48. \, 50. 14, 50. 26, 50. 41, 51. 2 616, 48. Temporary star : 1892, 48. Clusters : 996, 51. 1067, 51. 1119, 51. 1166, 51. 1295, 48. BOOTES, Map No. 11, 67. Stars : a (Arcturus), 66. 8, 71. e (Mirac), 71. 70. 1, 71. 193 194: PLEASURES OF THE TELESCOPE Stars : , 71. A*, 71. e,m IT, 70. 2 1772, 70. 2 1890 (39), 71. 2 1909 (44), 71. 2 1910 (279), 70. 2 1926, 71. CAMELOPARDALUS, Map No. 25, 133. Stars : 1, 134. 2, 134. 7, 135. 2 385, 134. 2 390, 134. Cluster : 940, 135. CANES VENATICI, Map No. 26, 137 ; Map No. 11, 67. Stars: 2,136. 12 (Cor Caroli), 136. 2 1606, 136. 2 1768 (25), 72. Cluster : 3936, 72. Nebula : 3572, 136. CANIS MAJOR, Map No. 2, 31. Stars : a (Sirius), 30. 5,33. /t,33. Clusters : 1454, 33. 1479, 33. 1512, 33. Variable : 7, 33. Nebula : 1511, 33. CANIS MINOR, Map No. 3, 34. Stars : a (Procyon), 36. 14, 36. 2 1126 (31 Can. Min. Bode), 36. CANCER, Map No. 4, 39. Stars : 43. *, 44. 66,44. 2 1223, 44. 2 1291, 44. 2 1311, 44. Clusters : Praesepe, 43. 1712, 44. CAPRICORNUS, Map No. 13, 83 ; Map No. 18, 107. Stars : a, 84. 0, 85. o,85. *, 85. | P, 85. , 29. 8,35. 2 627, 28. 11, 35. 2 629, 28. 2 921, 35. 2 652, 28. 2 938, 35. 2 725, 24. 2 950, 35. 2 728 (A 32), 28. INDEX 197 Stars : 2 729, 29. 2 747, 27. 2 750, 27. 2 795 (52), 27. 2 816, 29. 2 98 (i), 28. Clusters : 905, 29. 1184, 27. 1361, 29. 1376, 29. Nebula : Great Orion Nebula, 25. 1227, 23. 1267, 29. PEGASUS, Map No. 19, 110. Stars : 0, 109. 7, 109. e, 109. TJ, 109. PERSEUS, Map No. 24, 125. Stars : e, 129. C, 130. rj, 129. Clusters : 512, 129. 521, 129. Variable : & (Algol), 130. PISCES, Map No. 18, 107; Map No. 20, 112 ; Map No. 22, 119. Stars : a, 117. 117. *, H7. 55, 117. 65, 117. 66, 117. 77, 117. Variable : R, 118. SAGITTA, Map No. 16, 95. Stars : e, 94. C,94. 0,94. Nebula : 4572, 94. SAGITTARIUS, Map No. 12, 77 ; Map No. 13, 83. Stars : /i, 80. 54, 84. Clusters : M 25, 81. 4355, 81. 4361 (M 8), 81. 4397 (M 24), 81. Clusters : 4424, 84. Variables : R, 84. T, 84. U, 82. V, 82. SCORPIO, Map No. 12, 77. Stars : a (Antares), 75. ft 76. v, 76. 1,76. tr, 76. Temporary star : 1860, 78. Clusters : 4173, 78. 4183, 78. SCUTUM SOBIESKH, Map No. 12, 77 ; Map No. 13, 83. Stars: 22306,82. 2 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 : a, 86. ft 86. 8,86. 0,88. v, 86. Variable : R, 86. TAURUS, Map No. 23, 121. Stars : a (Aldebaran), 123. TJ (Alcyone), 120. 0, 123." K, 123. , 123. X, 123. 30, 122. 2 412 (7), 120. 2 430, 122. 2 674, 124. 2 716, 124. Clusters: Hyades, 120. Pleiades, 120. 1030, 124. 198 PLEASURES OF THE TELESCOPE Variable : \, 122. Nebulae : in Pleiades, 120. 1157 (Crab Net), 124. TRIANGULUM, Map No. 24, 125. Star: 6, 129. Nebula : 352, 129. URSA MAJOR. Stars: (Mizar), 135. i, 135. v, 135. f, 135.