The seventh planet from the Sun and the third largest, discovered by William
Herschel in 1781. It has a diameter
about 51,100 km, four times that of the Earth, and a mass 14.5 times Earth’s mass.
Uranus orbits the Sun at a distance over 19 times the
Earth-Sun distance. Although it takes about 84 years for Uranus
to make a revolution, it completes a fast rotation in only
17 and a half hours. Unlike the other planets, its axis of rotation
lies mostly in the plane of the Solar System.
Uranus is internally less active than the other giant planets, which
added to its larger distance from the Sun, makes it colder. It has
a dense atmosphere made of mostly molecular
hydrogen (83 percent) and helium (15 percent), with two percent
methane and traces of acetylene and other hydrocarbons.
The planet’s greenish-blue color is due to light
scattering as in Earth’s sky and the absorption of red light by its
small amount of atmospheric methane. Uranus has a ring system and 27 known satellites.
See also: L. Uranus, from Gk. Ouranos “heaven.”
In Gk. mythology he was the the primeval sky god, and
responsible for both the sunshine and the
rain. He was the son and husband of Gaia, the goddess of the
Earth and the father of Titans.
