URANUS. The next to the outermost mem ber of the solar system. lts mean distance from the sun is 1,782,000.000 miles; sidereal period, 84 years; eccentricity not quite or about the same as that of Jupiter; inclination to the ecliptic. 46'. It is about 66 times greater than the earth in volume and 15 times in mass, and its density and surface-gravity respectively are 0.22 and 0.9. In the telescope the planet appears as a greenish disk of about 4" diameter. The green ish tinge is explained as due to some unidentified subg.tance in the planet's atmosphere. Because of its immense distance, astronomers have been un able to gain much information concerning it. Spots and belts have been seen, but they are too faint to warrant any positive assertion, and the time of rotation of the planet is unknown. Ura nus was accidentally discovered by Sir William If rschel on March 13, 1781, and was named 'the Georgium Sidus' and 'Herschel,' but these names soon fell into disuse and the name of Uranus, suggested by Bode, finally prevailed. Herschel
announced the discovery as that of a comet, and its planetary nature was not demonstrated until three or four months later by Lexell, of Saint Petersburg. Before its detection by Herschel, Uranus had been recorded no less than 20 times as a fixed star, 12 times by Lemonier alone. These observations when compared with more re cent ones showed that the planet was wandering from its track. The attempts made to account for these irregularities led to the discovery of Neptune (q.v.).
Uranus has four satellites: Oberon and Titania were discovered by the elder Herschel. January II, 1787, the other two were discovered by Lassell, October 24, 1S51. They are estimated to vary in size from 200 to 500 miles in diameter. The plane of their orbit is in clined S2.2° to the plane of the ecliptic and their motions, like that of the satellite of Nep tune, is retrograde, i.e. from east to west. See PLANETS.