By far the largest of the planets is second in brilliancy to Venus, unlike which, however, it is a “superior” planet, having its orbit outside that of the earth. It is about five times as brilliant as Sirius, the brightest of the fixed stars.

The planet is a beautiful object when viewed with a telescope; it is probable that the markings are entirely due to its atmosphere, and that the actual surface of the planet is rarely visible. Jupiter has hardly yet cooled from the condition of incandescence, and it is only slightly solidified. It possesses eight satellites, four of which were discovered by Galileo when he applied the telescope first to the investigation of the heavens. By means of these satellites the first observations of the velocity of light were made. A fifth was discovered in 1892 at the Lick Observatory.

Jupiter  (´pit-er ); called Zeus (zūs ) by the Greeks.—King of heaven, and greatest of the Olympian gods; was a son of Saturn and Rhea. He dwelt on Mount Olympus, in Thessaly. He was the father and supreme ruler of gods and men. His first wife was Metis (q.v.). By Juno, his second wife, he had two sons, Mars and Vulcan, and one daughter, Hebe. The eagle, the oak, and doves were sacred to Jupiter. He was armed with thunderbolts, and surrounded with thick clouds, the former being provided for him by the Cyclops who worked under the direction of Vulcan. Jupiter was regarded as the special protector of Rome, and had a temple on the Capitol. He was looked upon as the guardian of law and the protector of justice and virtue. He was also the ruler of the lower air, hence rain and storms were supposed to come from him. In this connection the Romans applied the surname Pluvius  (i. e. the rain-bringer) to him, and special sacrifices were offered to him during long-protracted droughts.

Grand Results of the Discovery of Jupiter's Satellites

This discovery, one of the first fruits of the invention of the telescope, and of Galileo's early and happy idea of directing its newly-found powers to the examination of the heavens, forms one of the most memorable epochs in the history of astronomy. The first astronomical solution of the great problem of the longitude, practically the most important for the interests of mankind which has ever been brought under the dominion of strict scientific principles, dates immediately from this discovery. The final and conclusive establishment of the Copernican system of astronomy may also be considered as referable to the discovery and study of this exquisite miniature system, in which the laws of the planetary motions, as ascertained by Kepler, and specially that which connects their periods and distances, were specially traced, and found to be satisfactorily maintained. And (as if to accumulate historical interest on this point) it is to the observation of the eclipses of Jupiter's satellites that we owe the grand discovery of the aberration of light, and the consequent determination of the enormous velocity of that wonderful element—192,000 miles per second. Mr. Dawes, in 1849, first noticed the existence of round, well-defined, bright spots on the belts of Jupiter. They vary in situation and number, as many as ten having been seen on one occasion. As the belts of Jupiter have been ascribed to the existence of currents analogous to our trade-winds, causing the body of Jupiter to be visible through his cloudy atmosphere, Sir John Herschel conjectures that those bright spots may possibly be insulated masses of clouds of local origin, similar to the cumuli which sometimes cap ascending columns of vapour in our atmosphere.

It would require nearly 1300 globes of the size of our earth to make one of the bulk of Jupiter. A railway-engine travelling at the rate of thirty-three miles an hour would travel round the earth in a month, but would require more than eleven months to perform a journey round Jupiter.

FIG. 16.
FIG. 17.

Jupiter is by far the largest of the planets, it is 87,030  miles in diameter, and placed at the enormous distance of 494,000,000 miles from the sun. This great planet takes 12 years and 52 days to perform its circuit; it turns upon its axis in 9 hours 55 minutes, a surprisingly short time considering the immensity of its bulk. As a result of this rapid motion Jupiter is very far removed from the form of a true sphere, for the oblate form of heavenly bodies is caused by their rotatory motion, and the centrifugal force set up by it. In fig. 16 is an outline of the earth and Jupiter, showing their relative size. It has no phases, like those planets which are nearer to the sun than the earth, its great distance preventing this, as may be seen in fig. 17, in which the earth (e e ) is placed at the two widest lateral positions of its orbit, but the earth is too near the sun, in proportion to the great distance of Jupiter, to allow any part of the latter to come within the range of vision, except that which is illuminated by the sun. This planet is high up in the heavens the greater number of nights in the year, and is therefore a very conspicuous object. It also presents a  most beautiful appearance through a good telescope, its vast size causing it to look larger than those which are much nearer; it has several shadowy belts across it, which are supposed to be openings in the strata of clouds which surround it, drawn into ring-like forms by the rotation of the planet, these are shown in fig. 18. It being probable that this great planet is surrounded by strata of the densest clouds which only open in the tropical region, its inhabitants therefore, (if there be any) get but a glimpse of the firmanent and its stars through them, in those situations at or near to the planet's equator. These dense clouds serve a very useful purpose in regions so very far removed from the source of heat, for if radiation were permitted to go on freely from the surface of the planet the sun's rays would be too feeble to compensate for it, and the cold would be intense; but the clouds reflect back the heat radiated from the surface and keep in what little heat is received at that great distance. Jupiter has four satellites or moons, which revolve round it as our moon does round this earth.

FIG. 18.