Astronomy for Amateurs

the speed of which may be as great as 72 kilometers (45 miles) in the first second if we meet the star shower directly; the average rate, however, does not exceed 30 to 40 kilometers (19 to 25 miles), for these meteors nearly always cross our path obliquely. The height at which they arrive is usually 110 kilometers (68 miles), and 80 kilometers (50 miles) at the moment of disappearance of the meteor; but[Pg 194] shooting stars have been observed at 300 kilometers (186 miles). The friction caused by this collision high up in the atmosphere transforms the motion into heat. The molecules incandesce, and burn like true stars with a brilliancy that is often magnificent. But their glory is of short duration. The excessive heat resulting from the shock consumes the poor firefly; its remains evaporate, and drop slowly to the Earth, where they are deposited on the surface of the soil in a sort of ferruginous dust mixed with carbon and nickel. Some one hundred and forty-six milliards of them reach us annually, as seen by the unaided eye, and many more in the telescope; the effect of these showers of meteoric matter is an insensible increase in the mass of our globe, a slight lessening of its rotary motion, and the acceleration of the lunar movements of revolution. Although the appearance of shooting stars is a common enough phenomenon, visible every night of the year, there are certain times when they arrive in swarms, from different quarters of the sky. The most remarkable dates in this connection are the night of August 10th and the morning of November 14th. Every one knows the shooting stars of August 10th, because they arrive in the fine warm summer evenings so favorable to general contemplation of the Heavens. The [Pg 195]phenomenon lasts till the 12th, and even beyond, but the maximum is on the 10th. When the sky is very clear, and there is no moon, hundreds of shooting stars can be counted on those three nights, sometimes thousands. They all seem to come from the same quarter of the Heavens, which is called the radiant, and is situated for the August swarm in the constellation of Perseus, whence they have received the name of Perseids. Our forefathers also called them the tears of St. Lawrence, because the feast of that saint is on the same date. These shooting stars describe a very elongated ellipse, and their orbit has been identified with that of the Great Comet of 1862. The shower of incandescent asteroids on November 14th is often much more abundant than the preceding. In 1799, 1833, and 1866, the meteors were so numerous that they were described as showers of rain, especially on the first two dates. For several hours the sky was furrowed with falling stars. An English mariner, Andrew Ellicot, who made the drawing we reproduce (Fig. 55), described the phenomenon as stupendous and alarming (November 12, 1799, 3 A.M.). The same occurred on November 13, 1833. The meteors that scarred the Heavens on that night were reckoned at 240,000. These shooting stars received the name of Leonids, because their radiant is situated in the constellation of the Lion. [Pg 196] Fig. 55.—Shooting Stars of November 12, 1799. From a contemporary drawing. This swarm follows the same orbit as the comet of 1866, which travels as far as Uranus, and comes back to[Pg 197] the vicinity of the Sun every thirty-three years. Hence we were entitled to expect another splendid apparition in 1899, but the expectations of the astronomers were disappointed. All the preparations for the appropriate reception of these celestial visitors failed to bring about the desired result. The notes made in observatories, or in balloons, admitted of the registration of only a very small number of meteors. The maximum was thirteen. During that night, some 200 shooting stars were counted. There were more in 1900, 1901, and, above all, in 1902. This swarm has become displaced. The night of November 27th again is visited by a number of shooting stars that are the disaggregated remains of the Comet of Biela. This comet, discovered by Biela in 1827, accomplished its revolution in six and a half years, and down to 1846 it responded punctually to the astronomers who expected its return as fixed by calculation. But on January 13, 1846, the celestial wanderer broke in half: each fragment went its own way, side by side, to return within sight from the Earth in 1852. It was their last appearance. That year the twin comets could still be seen, though pale and insignificant. Soon they vanished into the depths of night, and never appeared again. They were looked for in vain, and were despaired of, when on November 27, 1872, instead of the shattered comet,[Pg 198] came a magnificent rain of shooting stars. They fell through the Heavens, numerous as the flakes of a shower of snow. The same phenomenon recurred on November 27, 1885, and confirmed the hypothesis of the demolition and disaggregation of Biela's Comet into shooting stars. There is an immense variety in the brilliancy of the shooting stars, from the weak telescopic sparks that vanish like a flash of lightning, to the incandescent bolides or fire-balls that explode in the atmosphere. Fig. 56 shows an example of these, and it represents a fire-ball observed at the Observatory of Juvisy on the night of August 10, 1899. It arrived from Cassiopeia, and burst in Cepheus. This phenomenon may occur by day as well as by night. It is often accompanied by one or several explosions, the report of which is sometimes perceptible to a considerable distance, and by a shower of meteorites. The globe of fire bursts, and splits up into luminous fragments, scattered in all directions. The different parts of the fire-ball fall to the surface of the Earth, under the name of aerolites, or rather of uranoliths, since they arrive from the depths of space, and not from our atmosphere. [Pg 199] From the most ancient times we hear of showers of uranoliths to which popular superstitions were attached; and the Greeks even gave the name of Sideros to iron, the first iron used having been sidereal. Fig. 56.—Fire-Ball seen from the Observatory at Juvisy, August 10, 1899. [Pg 200] Fig. 57.—Explosion of a Fire-Ball above Madrid, February 10, 1896. No year passes without the announcement of several showers of uranoliths, and the phenomenon sometimes causes great alarm to those who witness it. One of the most remarkable explosions is that which occurred above Madrid, February 10, 1896, a fragment from which,[Pg 201] sent me by M. Arcimis, Director of the Meteorological Institute, fell immediately in front of the National Museum (Fig. 57). The phenomenon occurred at 9.30 A.M., in brilliant sunshine. The flash of the explosion was so dazzling that it even illuminated the interior of the houses; an alarming clap of thunder was heard seventy seconds after, and it was believed that an explosion of dynamite had occurred. The fire-ball burst at a height of fourteen miles, and was seen as far as 435 miles from Madrid! In one of Raphael's finest pictures (The Madonna of Foligno) a fire-ball may be seen beneath a rainbow (Fig. 58), the painter wishing to preserve the remembrance of it, as it fell near Milan, on September 4, 1511. This picture dates from 1512. The dimensions of these meteorites vary considerably; they are of all sizes, from the impalpable dust that floats in the air, to the enormous blocks exposed in the Museum of Natural History in Paris. Many of them weigh several million pounds. That represented below fell in Mexico during the shower of meteors of November 27, 1885. It weighed about four pounds. [Pg 202] Fig. 58.—Raphael's Fire-Ball (The Madonna of Foligno). [Pg 203] These bolides and uranoliths come to us from the depths of space; but they do not appear to have the same origin as the shooting stars. They may arise from worlds destroyed by explosion or shock, or even from planetary volcanoes. The lightest of them may have been expelled from the volcanoes of the Moon. Some of the most massive, in which iron predominates, may even have issued from the bowels of the Earth, projected into space by some volcanic explosion, at an epoch when our globe was perpetually convulsed by cataclysms of extraordinary violence. They return to us to-day after being removed from the Earth to distances proportional to the initial speed imparted to them. This origin seems the more admissible as the stones that fall from the skies exhibit a mineral composition identical with that of the terrestrial materials. Fig. 59.—A Uranolith. [Pg 204] In any case, these uranoliths bring us back at least by their fall to our Earth, and from henceforward we will remain upon it, to study its position in space, and to take account of the place it fills in the Universe, and of the astronomical laws that govern our destiny. [Pg 205]