BELTS

, Fasciæ, in Astronomy, two zones or girdles surrounding the planet Jupiter, brighter than the rest of his body, and terminated by parallel lines. They are observed however to be sometimes broader and sometimes narrower, and not always occupying exactly the same part of the dise. Jupiter's belts were first observed and described by Huygens, in his Syst. Saturn. Dark spots have often been observed on the belts of Jupiter; and M. Cassini observed a permanent one on the northern side of the most southern belt, by which he determined the length of Jupiter's days, or the time in which the planet revolves upon its axis, which is 9h. 56m. Some astronomers suppose that these belts are seas, which alternately cover and leave bare large tracts of the planet's surface: and that the spots are gulphs in those seas, which are sometimes dry, and sometimes full. But Azout conceived that the spots are protuberances of the belts; and others | again are of opinion that the transparent and moveable spots are the shadows of Jupiter's satellites.

Cassini also speaks of the belts of Saturn; being three dark, straight, parallel bands, or fasciæ, on the disc of that planet. But it does not appear that Saturn's belts adhere to his body, as those of Jupiter do; but rather that they are large dark rings surrounding the planet at a distance. Some imagine that they are clouds in the atmosphere of Saturn, though it would seem that the middlemost is the shadow of his ring.