The Heavens Above: A Popular Handbook of Astronomy

by J. A. Gillet; W. J. Rolfe

Uranus.

275. Orbit and Dimensions of Uranus.—Uranus, the smallest of the outer group of planets, has a diameter of nearly thirty-two thousand miles. It is a little less dense than Jupiter, and its mean distance from the sun is about seventeen hundred and seventy millions of miles. Its orbit has about the same eccentricity as that of Jupiter, and is inclined less than a degree to the ecliptic. Uranus makes a revolution around the sun in eighty-four years, moving at the rate of a little over four miles a second. It is visible to the naked eye as a star of the sixth magnitude.

As seen in a large telescope, the planet has a decidedly sea-green color; but no markings have with certainty been detected on its disk, so that nothing is really known with regard to its rotation. Fig. 301 shows the comparative size of Uranus and the earth.

Fig. 301.

276. Discovery of Uranus.—This planet was discovered by Sir William Herschel in March, 1781. He was engaged at the time in examining the small stars of the constellation Gemini, or the Twins. He noticed that this object which had attracted his attention had an appreciable disk, and therefore could not be a star. He also perceived by its motion that it could not be a nebula; he therefore concluded that it was a comet, and announced his discovery as such. On attempting to compute its orbit, it was soon found that its motions could be accounted for only on the supposition that it was moving in a circular orbit at about twice the distance of Saturn from the sun. It was therefore recognized as a new planet, whose discovery nearly doubled the dimensions of the solar system as it was then known.

277. The Name of the Planet.—Herschel, out of compliment to his patron, George III., proposed to call the new planet Georgium Sidus (the Georgian Star); but this name found little favor. The name of Herschel was proposed, and continued in use in England for a time, but did not meet with general approval. Various other names were suggested, and finally that of Uranus was adopted.

Fig. 302.

278. The Satellites of Uranus.—Uranus is accompanied by four satellites, whose orbits are shown in Fig. 302. These satellites are remarkable for the great inclination of their orbits to the plane of the planet's orbit, amounting to about eighty degrees, and for their retrograde motion; that is, they move from east to west, instead of from west to east, as in the case of all the planets and of all the satellites previously discovered.