Astronomy for Amateurs

rare and terrible objects that no one dared to contemplate. To-day they may be counted by hundreds. They have lost in prestige and in originality; but science is the gainer, since she has thus endowed the solar system with new members. No year passes without the announcement of three or four new arrivals. But the fine apparitions that attract general attention by their splendor are rare enough. These eccentric visitors do not resemble the planets, for they have no opaque body like the Earth, Venus, Mars, or any of the rest. They are transparent nebulosities, of extreme lightness, without mass nor density. We have just photographed the comet of the moment, July, 1903: the smallest stars are visible through its tail, and even through the nucleus. [Pg 184] They arrive in every direction from the depths of space, as though to reanimate themselves in the burning, luminous, electric solar center. Attracted by some potent charm toward this dazzling focus, they come inquisitive and ardent, to warm themselves at its furnace. At first pale and feeble, they are born again when the Sun caresses them with his fervid heat. Their motions accelerate, they haste to plunge wholly into the radiant light. At length they burst out luminous and superb, when the day-star penetrates them with his burning splendor, illuminates them with a marvelous radiance, and crowns them with glory. But the Sun is generous. Having showered benefits upon these gorgeous celestial butterflies that flutter round him as round some altar of the gods, he grants them liberty to visit other heavens, to seek fresh universes.... The original parabola is converted into an ellipse, if the imprudent adventurer in returning to the Sun passes near some great planet, such as Jupiter, Saturn, Uranus, or Neptune, and suffers its attraction. It is then imprisoned by our system, and can no longer escape from it. After reenforcement at the solar focus, it must return to the identical point at which it felt the first pangs of a new destiny. Henceforward, it belongs to our celestial family, and circles in a closed curve.[Pg 185] Otherwise, it is free to continue its rapid course toward other suns and other systems. As a rule, the telescope shows three distinct parts in a comet. There is first the more brilliant central point, or nucleus, surrounded by a nebulosity called the hair, or brush, and prolonged in a luminous appendix stretching out into the tail. The head of the comet is the brush and the nucleus combined. Fig. 53.—The tails of Comets are opposed to the Sun. It is usually supposed that the tail of a comet follows it throughout the course of its peregrinations. Nothing of the kind. The appendix may even precede the nucleus; it is always opposite the Sun,—that is to say, it is situated on the prolongation of a straight line, starting from the Sun, and passing through the nucleus (Fig. 53). The tail does not exist, so long as the comet is at a distance from the orb of day; but in approaching the Sun, the nebulosity is heated and dilates, giving birth[Pg 186] to those mysterious tails and fantastic streamers whose dimensions vary considerably for each comet. The dilations and transformations undergone by the tail suggest that they may be due to a repulsive force emanating from the Sun, an electric charge transmitted doubtless through the ether. It is as though Phœbus blew upon them with unprecedented force. Telescopic comets are usually devoid of tail, even when they reach the vicinity of the Sun. They appear as pale nebulosities, rounded or oval, more condensed toward the center, without, however, showing any distinct nucleus. These stars are only visible for a minute fraction of their course, when they reach a point not far from the Sun and the terrestrial orbit. The finest comets of the last century were those of 1811, 1843, 1858, 1861, 1874, 1880, 1881, and 1882. The Great Comet of 1811, after spreading terror over certain peoples, notably in Russia, became the providence of the vine-growers. As the wine was particularly good and abundant that year, the peasants attributed this happy result to the influence of the celestial visitant. In 1843 one of these strange messengers from the Infinite appeared in our Heavens. It was so brilliant that it was visible in full daylight on February 28th, alongside of the Sun. This splendid comet was [Pg 187]accompanied by a marvelous rectilinear tail measuring 300,000,000 kilometers (186,000,000 miles) in length, and its flight was so rapid that it turned the solar hemisphere at perihelion in two hours, representing a speed of 550 kilometers (342 miles) a second. But the most curious fact is that this radiant apparition passed so near the Sun that it must have traversed its flames, and yet emerged from them safe and sound. Noteworthy also was the comet of 1858 (Fig. 49), discovered at Florence by Donati. Its tail extended to a length of 90,000,000 kilometers (55,900,000 miles), and its nucleus had a diameter of at least 900 kilometers (559 miles). It is a curious coincidence that the wine was remarkably excellent and abundant in that year also. The comet of 1861 almost rivaled the preceding. Coggia's Comet, in 1874, was also remarkable for its brilliancy, but was very inferior to the last two. Finally, the latest worthy of mention appeared in 1882. This magnificent comet also touched the Sun, traveling at a speed of 480 kilometers (299 miles) per second. It crossed the gaseous atmosphere of the orb of day, and then continued its course through infinity. On the day of, and that following, its perihelion, it could be detected with the unaided eye in full daylight, enthroned in the[Pg 188] Heavens beside the dazzling solar luminary. For the rest, it was neither that of 1858 nor of 1861. Since 1882 we have not been favored with a visit from any fine comet; but we are prepared to give any such a reception worthy of their magnificence: first, because now that we have fathomed them we are no longer awestruck; second, because we would gladly study them more closely. In short, these hirsute stars, whose fantastic appearance impressed the imagination of our ancestors so vividly, are no longer formidable. Their mass is inconsiderable; they seem to consist mainly of the lightest of gases. Analysis of their incandescence reveals a spectrum closely resembling that of many nebulæ; the presence of carbon is more particularly obvious. Even the nucleus is not solid, and is often transparent. It is fair to say that the action of a comet might be deleterious if one of these orbs were to arrive directly upon us. The transformation of motion into heat, and the combination of the cometary gases with the oxygen of our atmosphere might produce a conflagration, or a general poisoning of the atmosphere. But the collision of a comet with a planet is almost an impossibility. This phenomenon could only occur if the comet crossed the planetary orbit at the exact[Pg 189] moment at which the planet was passing. When we think of the immensity of space, of the extraordinary length of way traversed by a world in its annual journey round the Sun, and the speed of its rotation, we see why this coincidence is hardly likely to occur. Thus, among the hundreds of comets catalogued, a few only cut the terrestrial orbit. One of them, that of 1832, traversed the path of our globe in the nights of October 29 and 30 in that year; but the Earth only passed the same point thirty days later, and at the critical period was more than 80,000,000 kilometers (50,000,000 miles) away from the comet. On June 30, 1861, however, the Earth passed through the extremity of the tail of the Great Comet of that year. No one even noticed it. The effects were doubtless quite immaterial. In 1872 we were to collide with Biela's Comet, lost since 1852; now, as we shall presently see, we came with flying colors out of that disagreeable situation, because the comet had disintegrated, and was reduced to powder. So we may sleep in peace as regards future danger likely to come to us from comets. There is little fear of the destruction of humanity by these windy bags. These ethereal beauties whose blond locks float carelessly upon the azure night are not concerned with us; they seem to have no other preoccupation than to[Pg 190] race from sun to sun, visiting new Heavens, indifferent to the astonishment they produce in us. They speed restlessly and tirelessly through infinity; they are the Amazons of space. What suns, what worlds must they have visited since the moment of their birth! If these splendid fugitives could relate the story of their wanderings, how gladly should we listen to the enchanting descriptions of the various abodes they have journeyed to! But alas! these mysterious explorers are dumb; they tell none of their secrets, and we must needs respect their enigmatic silence. Yet, some of them have left us a modest token of remembrance, an almost impalpable nothing, sufficient, however, to enable us to address our thanks to the considerate messenger. Can there be any one upon the Earth who has not been struck by the phosphorescent lights that glide through the somber night, leaving a brilliant silver or golden track—the luminous, ephemeral trail of a meteor? Sometimes, when Night has silently spread the immensity of her wings above the weary Earth, a shining speck is seen to detach itself in the shades of evening from the starry vault, shooting lightly through the constellations to lose itself in the infinitude of space. [Pg 191] Fig. 54.—A Meteor. These bewitching sparks attract our eyes and chain our senses. Fascinating celestial fireflies, their[Pg 192] dainty flames dart in every direction through space, sowing the fine dust of their gilded wings upon the fields of Heaven. They are born to die; their life is only a breath; yet the impression which they make upon the imagination of mortals is of the profoundest. The young girl dreaming in the delicious tranquillity of the transparent night smiles at this charming sister in the Heavens (Fig. 54). What can not this adorable star announce to the tender and loving heart? Is it the shy messenger of the happiness so long desired? Its unpremeditated appearance fills the soul with a ray of hope and makes it tremble. It is a golden beam that glides into the heart, expanding it in the thrills of a sudden and ephemeral pleasure.... The radiant meteor seems to quit the velvet of the deep blue sky to respond to the appeal of the imploring voice that seeks its succor. What secrets has it not surprised! And who bears malice against it? It is the friend of the betrothed who invoke its passage to confide their wishes, and associate it with their dreams. Tradition holds that if a wish be formulated during the visible passage of a meteor it will certainly be fulfilled before the year is out. Between ourselves, however, this is but a surviving figment of the ancestral imagination, for this celestial jewel takes no such active part in the doings of Humanity.... Besides, try to express a wish distinctly in a second! [Pg 193] It is a curious fact that while comets have so often spread terror on the Earth, shooting stars should on the contrary have been regarded with benevolent feelings at all times. And what is a shooting star? These dainty excursionists from the celestial shores are not, as is supposed, true stars. They are atoms, nothings, minute fragments deriving in general from the disintegration of comets. They come to us from a vast distance, from millions on millions of miles, and circle in swarms around the Sun, following a very elongated ellipse which closely resembles that of the cometary orbit. Their flight is extremely rapid, reaching sometimes more than 40 kilometers (25 miles) per second, a cometary speed that is, as we have seen, greatly above that of our terrestrial vehicle, which amounts to 29 to 30 kilometers (about 19 miles). These little corpuscles are not intrinsically luminous; but when the orbit of a swarm of meteors crosses our planet, a violent shock arises,