Fig. 47.—Saturn.
The dipping of Saturn's axis of rotation is much the same as our own. Hence we conclude that the seasons of this planet are analogous to ours in relative intensity. Only upon this far-off world each season lasts for seven years. At the distance at which it gravitates in space, the heat and light which it receives from the Sun are 90 times less active than such as reach our selves; but it apparently possesses an atmosphere of great density, which may be constituted so that the heat is preserved, and the planet maintained in a calorific condition but little inferior to our own.
In the telescope, the disk of Saturn exhibits large belts that recall those of Jupiter, though they are broader and less accentuated (Fig. 47). There are doubtless zones of clouds or rapid currents circulating in the atmosphere. Spots are also visible whose displacement assists in calculating the diurnal motions of this globe.
The most extraordinary characteristic of this strange world is, however, the existence of a vast ring, which is almost flat and very large, and entirely envelops the body of the planet. It is suspended in the Saturnian sky, like a gigantic triumphal arch, at a height of some 20,000 kilometers (12,400 miles) above the equator. This splendid arch is circular, like an immense crown illuminated by the Sun. From here we only see it obliquely, and it appears to us elliptical; a part of the ring seems to pass in front of Saturn, and its shadow is visible on the planet, while the opposite part passes behind.
This ring, which measures 284,000 kilometers (176,080 miles) in diameter, and less than 100 kilometers (62 miles) in breadth, is divided into three distinct zones: the exterior is less luminous than the center, which is always brighter than the planet itself; the interior is very dark, and spreads out like a dusky and faintly transparent veil, through which Saturn can be distinguished.
What is the nature of these vast concentric circles that surround the planet with a luminous halo? They are composed of an innumerable number of particles, of a quantity of cosmic fragments, which are swept off in a rapid revolution, and gravitate round the planet at variable speed and distance. The nearer particles must accomplish their revolution in 5 hours, 50 minutes, and the most distant in about 12 hours, 5 minutes, to prevent them from being merged in the surface of Saturn: their own centrifugal force sustains them in space.
Fig. 48.—Varying perspective of Saturn's Rings, as seen from the Earth.
With a good glass the effect of these rings is most striking, and one can not refrain from emotion on contemplating this marvel, whereby one of the brothers of our terrestrial country is crowned with a golden diadem. Its aspects vary with its perspective relative to the Earth, as may be seen from the subjoined figure (Fig. 48).