Astronomy for Amateurs

end of seventeen months, to the terror of the peoples, who saw in it the harbinger of the world's end: that of 1604, in the Constellation of the Serpent, which shone for a year; of 1866, of second magnitude, in the Northern Crown,[Pg 78] which appeared for a few weeks only; of 1876, in the Swan; of 1885, in the Nebula of Andromeda; of 1891, in the Charioteer; and quite recently, of 1901, in Perseus. These temporary stars, which appear spontaneously to the observers on the Earth, and quickly vanish again, are doubtless due to collisions, conflagrations, or celestial cataclysms. But we only see them long after the epoch at which the phenomena occurred, years upon years, and centuries ago. For instance, the conflagration photographed by the author in 1901, in Perseus, must have occurred in the time of Queen Elizabeth. It has taken all this time for the rays of light to reach us. The Heavens are full of surprises, on which we can bestow but a fleeting glance within these limits. They present a field of infinite variety. Who has not noticed the Milky Way, the pale belt that traverses the entire firmament and is so luminous on clear evenings in the Constellations of the Swan and the Lyre? It is indeed a swarm of stars. Each is individually too small to excite our retina, but as a whole, curiously enough, they are perfectly visible. With opera-glasses we divine the starry constitution: a small telescope shows us marvels. Eighteen millions of stars were counted there with the gauges of William Herschel. Now this Milky Way is a symbol, not of the Universe,[Pg 79] but of the Universes that succeed each other through the vast spaces to Infinity. Our Sun is a star of the Milky Way. It surrounds us like a great circle, and if the Earth were transparent, we should see it pass beneath our feet as well as over our heads. It consists of a very considerable mass of star-clusters, varying greatly in extent and number, some projected in front of others, while the whole forms an agglomeration. Fig. 21.—The Star-Cluster in Hercules. Among this mass of star-groups, several thousands of which are already known to us, we will select one of the most curious, the Cluster in Hercules, which can be[Pg 80] distinguished with the unaided eye, between the stars η and ζ of that constellation. Many photographs of it have been taken in the author's observatory at Juvisy, showing some thousands of stars; and one of these is reproduced in the accompanying figure (Fig. 21). Is it not a veritable universe? Fig. 22.—The Star-Cluster in the Centaur. Another of the most beautiful, on account of its regularity, is that of the Centaur (Fig. 22). These groups often assume the most extraordinary shapes in the telescope, such as crowns, fishes, crabs, open mouths, birds with outspread wings, etc. We must also note the gaseous nebulæ, universes in[Pg 81] the making, e.g., the famous Nebula in Orion, of which we obtained some notion a while ago in connection with its sextuple star: and also that in Andromeda (Fig. 23). Fig. 23.—The Nebula in Andromeda. [Pg 82] Fig. 24.—Nebula in the Greyhounds. Perhaps the most marvelous of all is that of the Greyhounds, which evolves in gigantic spirals round a dazzling focus, and then loses itself far off in the recesses of space. Fig. 24 gives a picture of it. [Pg 83] Fig. 25.—The Pleiades. Without going thus far, and penetrating into telescopic depths, my readers can get some notion of these star-clusters with the help of a small telescope or opera-glasses, or even with the unaided eye, by looking at the beautiful group of the Pleiades, already familiar to us on another page, and using it as a test of vision. The little map subjoined (Fig. 25) will be an assistance in recognizing them, and in estimating their magnitudes, which are in the following order: [Pg 84] Alcyone3.0. Electra4.5. Atlas4.6. Maia5.0. Merope5.5. Taygeta5.8. Pleione6.3. Celæno6.5. Asterope6.8. Good eyes distinguish the first six, sharp sight detects the three others. In the times of the ancient Greeks, seven were accounted of equal brilliancy, and the poets related that the seventh star had fled at the time of the Trojan War. Ovid adds that she was mortified at not being embraced by a god, as were her six sisters. It is probable that only the best sight could then distinguish Pleione, as in our own day. The angular distance from Atlas to Pleione is 5′. The length of this republic, from Atlas and Pleione to Celæno, is 4′/23″ of time, or 1°6′ of arc; the breadth, from Merope to Asterope, is 36′.[8] In the quadrilateral, the length from Alcyone to Electra is 36′, and the breadth from Merope to Maia 25′. To us it appears as though, if the Full Moon were placed in front of this group of nine stars, she would cover it entirely, for to the naked eye she appears much larger than all the Pleiades together. But this is not so. She only measures 31′, less than half the distance from Atlas to Celæno; she is hardly broader than the distance[Pg 85] from Alcyone to Atlas, and could pass between Merope and Taygeta without touching either of these stars. This is a perennial and very curious optical illusion. When the Moon passes in front of the Pleiades, and occults them successively, it is hard to believe one's eyes. The fact occurred, e.g., on July 23, 1897, during a fine occultation observed at the author's laboratory of Juvisy (Fig. 26). Fig. 26.—Occultation of the Pleiades by the Moon. Photography here discovers to us, not 6, 9, 12, 15, or 20 stars, but hundreds and millions. [Pg 86] These are the most brilliant flowers of the celestial garden. Fig. 27.—Stellar dial of the double star γ of the Virgin. We, alas, can but glance at them rapidly. In contemplating them we are transported into immensities both of space and time, for the stellar periods measured by these distant universes often overpower in their magnitude the rapid years in which our terrestrial days are estimated. For instance, one of the double stars we spoke of above, γ of the Virgin, sees its two components, translucent diamonds, revolve around their common center of gravity, in one hundred and eighty years. How many events took place in France, let us say, in a single year of this star!—The Regency, Louis XV, Louis XVI, the Revolution, Napoleon, Louis XVIII, Louis[Pg 87] Philippe, the Second Republic, Napoleon III, the Franco-German War, the Third Republic.... What revolutions here, during a single year of this radiant pair! (Fig. 27.) But the pageant of the Heavens is too vast, too overwhelming. We must end our survey. Our Milky Way, with its millions of stars, represents for us only a portion of the Creation. The illimitable abysses of Infinitude are peopled by other universes as vast, as imposing, as our own, which are renewed in all directions through the depths of Space to endless distance. Where is our little Earth? Where our Solar System? We are fain to fold our wings, and return from the Immense and Infinite to our floating island. [Pg 88]