The planet is certainly not in any way dependent on the sun for the extraordinary heat that everything indicates it to have, and its surface is brighter than it is believed it could be if shining only by the reflected light of the sun. This does not mean that Saturn is self-luminous; but it is nearly certain that it is extremely hot and glowing, and its brightness may be in part due to its own internal fires and the extremely luminous and dense atmosphere that surrounds it. It receives one hundred times less heat and light from the sun than we do. If it depended entirely upon the sun for its heat, the temperature would be nearly three hundred degrees below zero, Fahrenheit. It is probably not only very hot itself, but its heavy atmospheric envelope perhaps allows comparatively little heat to escape. Its surface is belted and spotted somewhat after the manner of Jupiter’s, but, being so much farther from us than Jupiter, it does not disclose its surface features with the same distinctness. Apparently it is much less turbulent than Jupiter; but even this we are not quite certain of, and it may seem more placid because we do not so well see its agitations. Like all the outer planets, it differs in its constitution from the earth and the other inner planets. Its atmosphere contains compounds with which we are not familiar, and the body of the planet itself is rarer and lighter, and less condensed, and in a much earlier stage of evolution than the earth and the small planets so comparatively near us. DAY AND NIGHT The length of Saturn’s day, or its period of rotation on its axis, is about ten hours and a quarter. Like Jupiter, it has slightly different rates of rotation in different latitudes, thus showing its lack of solidity. The rate of rotation has been determined, as in the case of Jupiter, by observation of the spots on its surface, which, while they are not exactly permanent, yet remain apparently in the same positions for months and even years at a time, and are thus sufficiently stable to measure a rotation of so short a time as ten hours.