Astronomy with an Opera-glass Part 3

The name Hercules sufficiently indicates the mythological origin of the constellation, and yet the Greeks did not know it by that name, for Aratus calls it "the Phantom whose name none can tell." The Northern Crown, according to fable, was the celebrated crown of Ariadne, and Lyra was the harp of Orpheus himself, with whose sweet music he charmed the hosts of Hades, and persuaded Pluto to yield up to him his lost Eurydice.

With the aid of the map you will be able to recognize the princ.i.p.al stars and star-groups in Hercules, and will find many interesting combinations of stars for yourself. An object of special interest is the celebrated star-cl.u.s.ter 13 M. You will find it on the map between the stars Eta ([eta]) and Zeta ([zeta]). While an opera-gla.s.s will only show it as a faint and minute speck, lying nearly between two little stars, it is nevertheless well worth looking for, on account of the great renown of this wonderful congregation of stars. Sir William Herschel computed the number of stars contained in it as about fourteen thousand.

It is roughly spherical in shape, though there are many straggling stars around it evidently connected with the cl.u.s.ter. In short, it is _a ball of suns_. The reader should not mistake what that implies, however.

These suns, though truly solar bodies, are probably very much smaller than our sun. Mr. Gore has computed their average diameter to be forty-five thousand miles, and the distance separating each from the next to be 9,000,000,000 miles. It may not be uninteresting to inquire what would be the appearance of the sky to dwellers within such a system of suns. Adopting Mr. Gore's estimates, and supposing 9,000,000,000 miles to be very nearly the uniform distance apart of the stars in the cl.u.s.ter, and forty-five thousand miles their uniform diameter, then, starting with a single star in the center, their arrangement might be approximately in concentric spherical sh.e.l.ls, situated about 9,000,000,000 miles apart. The first sh.e.l.l, counting outward from the center, would contain a dozen stars, each of which, as seen by an observer stationed upon a planet at the center of the cl.u.s.ter, would s.h.i.+ne eleven hundred times as bright as Sirius appears to us. The number of the stars in each sh.e.l.l would increase as they receded from the center in proportion to the squares of the radii of the successive sh.e.l.ls, while their luminosity, as seen from the center, would vary inversely as those squares. Still, the outermost stars--the total number being limited to fourteen or fifteen thousand--would appear to our observer at the center of the system about five times as brilliant as Sirius.

It is clear, then, that he would be dwelling in a sort of perpetual daylight. His planet might receive from the particular sun around which it revolved as brilliant a daylight as our sun gives to us, but let us see what would be the illumination of its night side. Adopting Zollner's estimate of the light of the sun as 618,000 times as great as that of the full moon, and choosing among the various estimates of the light of Sirius as compared with the sun 1/4000000000 as probably the nearest the truth, we find that the moon sends us about sixty-five hundred times as much light as Sirius does. Now, since the dozen stars nearest the center of the cl.u.s.ter would each appear to our observer eleven hundred times as bright as Sirius, all of them together would give a little more than twice as much light as the full moon sheds upon the earth. But as only half the stars in the cl.u.s.ter would be above the horizon at once we must diminish this estimate by one half, in order to obtain the amount of light that our supposit.i.tious planet would receive on its night side from the nearest stars in the cl.u.s.ter. And since the number of these stars increases with their distance from the center in the same ratio as their light diminishes, it follows that the total light received from the cl.u.s.ter would exceed that received from the dozen nearest stars as many times as there were spherical sh.e.l.ls in the cl.u.s.ter. This would be about fifteen times, and accordingly all the stars together would shed, at the center, some thirty times as much light as that of the moon.

Dividing this again by two, because only half of the stars could be seen at once, we find that the night side of our observer's planet would be illuminated with fifteen times as much light as the full moon sheds upon the earth.

It is evident, too, that our observer would enjoy the spectacle of a starry firmament incomparably more splendid than that which we behold.

Only about three thousand stars are visible to our una.s.sisted eyes at once on any clear night, and of those only a few are conspicuous, and two thirds are so faint that they require some attention in order to be distinguished. But the spectator at the center of the Hercules cl.u.s.ter would behold some seven thousand stars at once, the faintest of which would be five times as brilliant as the brightest star in our sky, while the brighter ones would blaze like nearing suns. One effect of this flood of starlight would be to shut out from our observer's eyes all the stars of the outside universe. They would be effaced in the blaze of his sky, and he would be, in a manner, shut up within his own little star-system, knowing nothing of the greater universe beyond, in which we behold his mult.i.tude of luminaries, diminished and blended by distance into a faintly s.h.i.+ning speck, floating like a silvery mote in a sunbeam.

If our observer's planet, instead of being situated in the center of the cl.u.s.ter, circled around one of the stars at the outer edge of it, the appearance of his sky would be, in some respects, still more wonderful, the precise phenomena depending upon the position of the planet's...o...b..t and the station of the observer. Less than half of his sky would be filled, at any time, by the stars of the cl.u.s.ter, the other half opening upon outer s.p.a.ce and appearing by comparison almost starless--a vast, cavernous expanse, with a few faint glimmerings out of its gloomy depths. The plane of the orbit of his planet being supposed to pa.s.s through the center of the spherical system, our observer would, during his year, behold the night at one season blazing with the splendors of the cl.u.s.tered suns, and at another emptied of brilliant orbs and faintly lighted with the soft glow of the Milky-Way and the feeble flickering of distant stars, scattered over the dark vault. The position of the orbit, and the inclination of the planet's axis might be such that the glories of the cl.u.s.ter would not be visible from one of its hemispheres, necessitating a journey to the other side of the globe to behold them.[B]

[B] A similar calculation of the internal appearances of the Hercules cl.u.s.ter, which I made, was published in 1887 in the "New York Sun."

Of course, it is not to be a.s.sumed that the arrangement of the stars in the cl.u.s.ter actually is exactly that which we have imagined. Still, whatever the arrangement, so long as the cl.u.s.ter is practically spherical, and the stars composing it are of nearly uniform size and situated at nearly uniform distances, the phenomena we have described would fairly represent the appearances presented to inhabitants of worlds situated in such a system. As to the possibility of the existence of such worlds and inhabitants, everybody must draw his own conclusions.

Astronomy, as a science, is silent upon that question. But there s.h.i.+ne the congregated stars, mingling their rays in a message of light, that comes to us across the gulf, proclaiming their brotherhood with our own glorious sun. Mathematicians can not unravel the interlocking intricacies of their orbits, and some would, perhaps _a priori_, have said that such a system was impossible, but the telescope has revealed them, and there they are! What purposes they subserve in the economy of the universe, who shall declare?

If you have a field-gla.s.s, by all means try it upon 13 M. It will give you a more satisfactory view than an opera-gla.s.s is capable of doing, and will magnify the cl.u.s.ter so that there can be no possibility of mistaking it for a star. Compare this compact cl.u.s.ter, which only a powerful telescope can partially resolve into its component stars, with 7 M. and 24 M., described before, in order to comprehend the wide variety in the structure of these aggregations of stars.

The Northern Crown, although a strikingly beautiful constellation to the naked eye, offers few attractions to the opera-gla.s.s. Let us turn, then, to Lyra. I have never been able to make up my mind which of three great stars is ent.i.tled to precedence--Vega, the leading brilliant of Lyra, Arcturus in Bootes, or Capella in Auriga. They are the three leaders of the northern firmament, but which of them should be called the chief, is very hard to say. At any rate, Vega would probably be generally regarded as the most beautiful, on account of the delicate bluish tinge in its light, especially when viewed with a gla.s.s. There is no possibility of mistaking this star because of its surpa.s.sing brilliancy. Two faint stars close to Vega on the east make a beautiful little triangle with it, and thus form a further means of recognition, if any were needed.

Your opera-gla.s.s will show that the floor of heaven is powdered with stars, fine as the dust of a diamond, all around the neighborhood of Vega, and the longer you gaze the more of these diminutive twinklers you will discover.

[Ill.u.s.tration: MAP 11.]

Now direct your gla.s.s to the northernmost of the two little stars near Vega, the one marked Epsilon ([epsilon]) in the map. You will perceive that it is composed of two stars of almost equal magnitude. If you had a telescope of considerable power, you would find that each of these stars is in turn double. In other words, this wonderful star which appears single to the una.s.sisted eye, is in reality quadruple, and there is reason to think that the four stars composing it are connected in pairs, the members of each pair revolving around their common center while the two pairs in turn circle around a center common to all. With a field-gla.s.s you will be able to see that the other star near Vega, Zeta ([zeta]), is also double, the distance between its components being three quarters of a minute, while the two stars in [epsilon] are a little less than 3' apart. The star Beta ([beta]) is remarkably variable in brightness. You may watch these variations, which run through a regular period of about 12 days, 21 hours, for yourself.

Between Beta and Gamma ([gamma]) lies the beautiful Ring nebula, but it is hopelessly beyond the reach of the optical means we are employing.

Let us turn next to the stars in the west. In consulting the accompanying map of Virgo and Bootes (Map No. 11), the observer is supposed to face the southwest, at the hours and dates mentioned above as those to which the circular map corresponds. He will then see the bright star Spica in Virgo not far above the horizon, while Arcturus will be half-way up the sky, and the Northern Crown will be near the zenith.

The constellation Virgo is an interesting one in mythological story.

Aratus tells us that the Virgin's home was once on earth, where she bore the name of Justice, and in the golden age all men obeyed her. In the silver age her visits to men became less frequent, "no longer finding the spirits of former days"; and, finally, when the brazen age came with the clangor of war:

"Justice, loathing that race of men, Winged her flight to heaven; and fixed Her station in that region Where still by night is seen The Virgin G.o.ddess near to bright Bootes."

The chief star of Virgo, Spica, is remarkable for its pure white light.

To my eye there is no conspicuous star in the sky equal to it in this respect, and it gains in beauty when viewed with a gla.s.s. With the aid of the map the reader will find the celebrated binary star Gamma ([gamma]) Virginis, although he will not be able to separate its components without a telescope. It is a curious fact that the star Epsilon ([epsilon]) in Virgo has for many ages been known as the Grape-Gatherer. It has borne this name in Greek, in Latin, in Persian, and in Arabic, the origin of the appellation undoubtedly being that it was observed to rise just before the sun in the season of the vintage.

It will be observed that the stars [epsilon], [delta], [gamma], [eta], and [beta], mark two sides of a quadrilateral figure of which the opposite corner is indicated by Denebola in the tail of Leo. Within this quadrilateral lies the marvelous Field of the Nebulae, a region where with adequate optical power one may find hundreds of these strange objects thronging together, a very storehouse of the germs of suns and worlds. Unfortunately, these nebulae are far beyond the reach of an opera-gla.s.s, but it is worth while to know where this curious region is, even if we can not behold the wonders it contains. The stars Omicron ([omicron]), Pi ([pi]), etc., forming a little group, mark the head of Virgo.

The autumnal equinox, or the place where the sun crosses the equator of the heavens on his southerly journey about the 21st of September, is situated nearly between the stars [eta] and [beta] Virginis, a little below the line joining them, and somewhat nearer to [eta]. Both [eta]

and [zeta] Virginis are almost exactly upon the equator of the heavens.

The constellation Libra, lying between Virgo and Scorpio, does not contain much to attract our attention. Its two chief stars, [alpha] and [beta], may be readily recognized west of and above the head of Scorpio.

The upper one of the two, [beta], has a singular greenish tint, and the lower one, [alpha], is a very pretty double for an opera-gla.s.s.

The constellation of Libra appears to have been of later date than the other eleven members of the zodiacal circle. Its two chief stars at one time marked the extended claws of Scorpio, which were afterward cut off (perhaps the monster proved too horrible even for its inventors) to form Libra. As its name signifies, Libra represents a balance, and this fact seems to refer the invention of the constellation back to at least three hundred years before Christ, when the autumnal equinox occurred at the moment when the sun was just crossing the western border of the constellation. The equality of the days and nights at that season readily suggests the idea of a balance. Milton, in "Paradise Lost,"

suggests another origin for the constellation of the Balance in the account of Gabriel's discovery of Satan in paradise:

"... Now dreadful deeds Might have ensued, nor only paradise In this commotion, but the starry cope Of heaven, perhaps, or all the elements At least had gone to wrack, disturbed and torn With violence of this conflict, had not soon The Eternal, to prevent such horrid fray, Hung forth in heaven his golden scales, yet seen Betwixt Astrea and the Scorpion sign."

Just north of Virgo's head will be seen the glimmering of Berenice's Hair. This little constellation was included among those described in the chapter on "The Stars of Spring," but it is worth looking at again in the early summer, on moonless nights, when the singular arrangement of the brighter members of the cl.u.s.ter at once strikes the eye.

[Ill.u.s.tration: BERENICE'S HAIR.]

Bootes, whose leading brilliant, Arcturus, occupies the center of our map, also possesses a curious mythical history. It is called by the Greeks the Bear-Driver, because it seems continually to chase Ursa Major, the Great Bear, in his path around the pole. The story is that Bootes was the son of the nymph Calisto, whom Juno, in one of her customary fits of jealousy, turned into a bear. Bootes, who had become a famous hunter, one day roused a bear from her lair, and, not knowing that it was his mother, was about to kill her, when Jupiter came to the rescue and s.n.a.t.c.hed them both up into the sky, where they have shone ever since. Lucan refers to this story when, describing Brutus's visit to Cato at night, he fixes the time by the position of these constellations in the heavens:

"'Twas when the solemn dead of night came on, When bright Calisto, with her s.h.i.+ning son, Now half the circle round the pole had run."

Bootes is not specially interesting for our purposes, except for the splendor of Arcturus. This star has possessed a peculiar charm for me ever since boyhood, when, having read a description of it in an old treatise on Uranography, I felt an eager desire to see it. As my search for it chanced to begin at a season when Arcturus did not rise till after a boy's bed-time, I was for a long time disappointed, and I shall never forget the start of surprise and almost of awe with which I finally caught sight of it, one spring evening, shooting its flaming rays through the boughs of an apple-orchard, like a star on fire.

When near the horizon, Arcturus has a remarkably reddish color; but, after it has attained a high elevation in the sky, it appears rather a deep yellow than red. There is a scattered cl.u.s.ter of small stars surrounding Arcturus, forming an admirable spectacle with an opera-gla.s.s on a clear night. To see these stars well, the gla.s.s should be slowly moved about. Many of them are hidden by the glare of Arcturus. The little group of stars near the end of the handle of the Great Dipper, or, what is the same thing, the tail of the Great Bear, marks the upraised hand of Bootes. Between Berenice's Hair and the tail of the Bear you will see a small constellation called Canes Venatici, the Hunting-Dogs. On the old star-maps Bootes is represented as holding these dogs with a leash, while they are straining in chase of the Bear.

You will find some pretty groupings of stars in this constellation.

And now we will turn to the east. Our next map shows Cygnus, a constellation especially remarkable for the large and striking figure that it contains, called the Northern Cross, Aquila the Eagle, the Dolphin, and the little asterisms Sagitta and Vulpecula. In consulting the map, the observer is supposed to face toward the east. In Aquila the curious arrangement of two stars on either side of the chief star of the constellation, called Altair, at once attracts the eye. Within a circle including the two attendants of Altair you will probably be able to see with the naked eye only two or three stars in addition to the three large ones. Now turn your gla.s.s upon the same spot, and you will see eight or ten times as many stars, and with a field-gla.s.s still more can be seen. Watch the star marked Eta ([eta]), and you will find that its light is variable, being sometimes more than twice as bright as at other times. Its changes are periodical, and occupy a little over a week.

The Eagle is fabled to have been the bird that Jupiter kept beside his throne. A constellation called Antinous, invented by Tycho Brahe, is represented on some maps as occupying the lower portion of the s.p.a.ce given to Aquila.

The Dolphin is an interesting little constellation, and the ancients said it represented the very animal on whose back the famous musician Arion rode through the sea after his escape from the sailors who tried to murder him. But some modern has dubbed it with the less romantic name of Job's Coffin, by which it is sometimes called. It presents a very pretty sight to the opera-gla.s.s.

Cygnus, the swan, is a constellation whose mythological history is not specially interesting, although, as remarked above, it contains one of the most clearly marked figures to be found among the stars, the famous Northern Cross. The outlines of this cross are marked with great distinctness by the stars Alpha ([alpha]), Epsilon ([epsilon]), Gamma ([gamma]), Delta ([delta]), and Beta ([beta]), together with some fainter stars lying along the main beam of the cross between [beta] and [gamma]. The star [beta], also called Albireo, is one of the most beautiful double stars in the heavens. The components are sharply contrasted in color, the larger star being golden-yellow, while the smaller one is a deep, rich blue. With a field-gla.s.s of 1.6-inch aperture and magnifying seven times I have sometimes been able to divide this pair, and to recognize the blue color of the smaller star.

It will be found a severe test for such a gla.s.s.

[Ill.u.s.tration: MAP 12.]

About half-way from Albireo to the two stars [zeta] and [epsilon] in Aquila is a very curious little group, consisting of six or seven stars in a straight row, with a garland of other stars hanging from the center. To see it best, take a field-gla.s.s, although an opera-gla.s.s shows it.

I have indicated the place of the celebrated star 61 Cygni in the map, because of the interest attaching to it as the nearest to us, so far as we know, of all the stars in the northern hemisphere, and with one exception the nearest star in all the heavens. Yet it is very faint, and the fact that so inconspicuous a star should be nearer than such brilliants as Vega and Arcturus shows how wide is the range of magnitude among the suns that light the universe. The actual distance of 61 Cygni is something like 650,000 times as great as the distance from the earth to the sun.

The star Omicron ([omicron]) is very interesting with an opera-gla.s.s.

The naked eye sees a little star near it. The gla.s.s throws them wide apart, and divides [omicron] itself into two stars. Now, a field-gla.s.s, if of sufficient power, will divide the larger of these stars again into two--a fine test.

Sweep around [alpha] and [gamma] for the splendid star-fields that abound in this neighborhood; also around the upper part of the figure of the cross. We are here in one of the richest parts of the Milky-Way.

Between the stars [alpha], [gamma], [epsilon], is the strange dark gap in the galaxy called the Coal-Sack, a sort of hole in the starry heavens. Although it is not entirely empty of stars, its blackness is striking in contrast with the brilliancy of the Milky-Way in this neighborhood. The divergent streams of the great river of light in this region present a very remarkable appearance.

[Ill.u.s.tration: MAP 13.]

Finally, we come to the great dragon of the sky. In using the map of Draco and the neighboring constellations, the reader is supposed to face the north. The center of the upper edge of the map is directly over the observer's head. One of the stories told of this large constellation is that it represents a dragon that had the temerity to war against Minerva. The G.o.ddess "seized it in her hand, and hurled it, twisted as it was, into the heavens round the axis of the world, before it had time to unwind its contortions." Others say it is the dragon that guarded the golden apples in the Garden of the Hesperides, and that was slain by the redoubtable Hercules. At any rate, it is plainly a monster of the first magnitude. The stars [beta], [gamma], [xi], [nu], and [mu] represent its head, while its body runs trailing along, first sweeping in a long curve toward Cepheus, and then bending around and pa.s.sing between the two bears. Try [nu] with your opera-gla.s.s, and if you succeed in seeing it double you may congratulate yourself on your keen sight. The distance between the stars is about 1'. Notice the contrasted colors of [gamma]

and [beta], the former being a rich orange and the latter white. As you sweep along the winding way that Draco follows, you will run across many striking fields of stars, although the heavens are not as rich here as in the splendid regions that we have just left. You will also find that Cepheus, although not an attractive constellation to the naked eye, is worth some attention with an opera-gla.s.s. The head and upper part of the body of Cepheus are plunged in the stream of the Milky Way, while his feet are directed toward the pole of the heavens, upon which he is pictured as standing. Cepheus, however, sinks into insignificance in comparison with its neighbor Ca.s.siopeia, but that constellation belongs rather to the autumn sky, and we shall pa.s.s it by here.

CHAPTER III.

THE STARS OF AUTUMN.

IN the "Fifth Evening" of that delightful, old, out-of-date book of Fontenelle's, on the "Plurality of Worlds," the Astronomer and the Marchioness, who have been making a wonderful pilgrimage through the heavens during their evening strolls in the park, come at last to the starry systems beyond the "solar vortex," and the Marchioness experiences a lively impatience to know what the fixed stars will turn out to be, for the Astronomer has sharpened her appet.i.te for marvels.