CHAPTER VI
THE PLANETS
B.—Jupiter, Saturn, Uranus, Neptune.
Before we attack the giant world of our system, we must halt for a few moments upon the minor planets which circulate between the orbit of Mars and that of Jupiter. These minute asters, little worlds, the largest of which measures scarcely more than 100 kilometers (62 miles) in diameter, are fragments of cosmic matter that once belonged to a vast ring, formed at the time when the solar system was only an immense nebula; and which, instead of condensing into a single globe coursing between Mars and Jupiter, split up into a considerable quantity of particles constituting at the present time the curious and highly interesting Republic of the Asteroids.
These lilliputian worlds at first received the names of the more celebrated of the minor mythological divinities—Ceres, Pallas, Juno, Vesta, etc., but as they rapidly increased in number, it was found necessary to call them by modern, terrestrial names, and more than one daughter of Eve, the Egeria of some astronomer, now has her name inscribed in the Heavens. The first minor planet was discovered on the first day of the nineteenth century, January 1, 1801, by Piazzi, astronomer at Palermo. While he was observing the small stars in the constellation of the Bull beneath the clear Sicilian skies, this famous astronomer noticed one that he had never seen before.
The next night, directing his telescope to the same part of the Heavens, he perceived that the fair unknown had moved her station, and the observations of the following days left him no doubt as to the nature of the visitor: she was a planet, a wandering star among the constellations, revolving round the Sun. This newcomer was registered under the name of Ceres.
Since that epoch several hundreds of them have been discovered, occupying a zone that extends over a space of more than 400 million kilometers (249,000,000 miles). These celestial globules are invisible to the naked eye, but no year passes without new and numerous recruits being added to the already important catalogue of these minute asters by the patient observers of the Heavens. To-day, they are most frequently discovered by the photographic method of following the displacement of the tiny moving points upon an exposed sensitive plate.