Astronomy for Amateurs

at a speed proportional to their distance. They number eight principal orbs, and may be divided into two quite distinct groups by which we may recognize them: the first comprises four planets, of relatively small dimensions in comparison with those of the second group, which are so voluminous that the least important of them is larger than the other four put together. In order of distance from the Sun, we first encounter: MERCURY, VENUS, THE EARTH, AND MARS These are the worlds that are nearest to the orb of day. The four following, and much more remote, are, still in order of distance: JUPITER, SATURN, URANUS, AND NEPTUNE This second group is separated from the first by a vast space occupied by quite a little army of minute planets, tiny cosmic bodies, the largest of which measures[Pg 110] little more than 100 kilometers (62 miles) in diameter, and the smallest some few miles only. The planets which form these three groups represent the principal members of the solar family. But the Sun is a patriarch, and each of his daughters has her own children who, while obeying the paternal influence of the fiery orb, are also obedient to the world that governs them. These secondary asters, or satellites, follow the planets in their course, and revolve round them in an ellipse, just as the others rotate round the Sun. Every one knows the satellite of the Earth, the Moon. All the other planets of our system have their own moons, some being even more favored than ourselves in this respect, and having several. Mars has two; Jupiter, five; Saturn, eight; Uranus, four; and Neptune, one (at least as yet discovered). In order to realize the relations between these worlds, we must appreciate their distances by arranging them in a little table: Distance inMillions ofKilometers.Distance inMillions ofMiles. Mercury5735 Venus10867 The Earth14993 Mars226140 Jupiter775481 Saturn1,421882 Uranus2,8311,755 Neptune4,4702,771 [Pg 111] The Sun is at the center (or, more properly speaking, at the focus, for the planets describe an ellipse) of this system, and controls them. Neptune is thirty times farther from the Sun than the Earth. These disparities of distance produce a vast difference in the periods of the planetary revolutions; for while the Earth revolves round the Sun in a year, Venus in 224 days, and Mercury in 88, Mars takes nearly 2 years to accomplish his journey, Jupiter 12 years, Saturn 29, Uranus 84, and Neptune 165. Even the planets and their moons do not represent the Sun's complete paternity. There are further, in the solar republic, certain vagabond and irregular orbs that travel at a speed that is often most immoderate, occasionally approaching the Sun, not to be consumed therein, but, as it appears, to draw from its radiant source the provision of forces necessary for their perigrinations through space. These are the Comets, which pursue an extremely elongated orbit round the Sun, to which at times they approximate very closely, at other times being excessively distant. And now to recapitulate our knowledge of the Solar Empire. In the first place, we see a colossal globe of fire dominating and governing the worlds that belong to him. Around him are grouped planets, in number eight principal, formed of solid and obscure matter, gravitating[Pg 112] round the central orb. Other secondary orbs, the satellites, revolve round the planets, which keep them within the sphere of their attraction. And lastly, the comets, irregular celestial bodies, track the whole extent of the great solar province. To these might be added the whirlwinds of meteors, as it were disaggregated comets, which also circle round the Sun, and give origin to shooting stars, when they come into collision with the Earth. Having now a general idea of our celestial family, and an appreciation of the potent focus that controls it, let us make direct acquaintance with the several members of which it is composed. [Pg 113]