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diameter of Uranus, surface of Uranus, largest planet, space probe, Roman mythology

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Uranus (planet), seventh planet in distance from the Sun, third largest planet in diameter, and fourth largest in mass in the solar system. Unlike other major planets, Uranus is tipped sideways on its axis of rotation. It experiences extreme seasons, and its 13 rings and 27 known moons revolve around its equator nearly vertically to the plane of its orbit around the Sun.

Because of its great size and mass, scientists classify Uranus as one of the giant or Jovian (Jupiter-like) planets—along with Jupiter, Saturn, and Neptune. Like more distant Neptune, Uranus is also classified as an ice giant planet, mainly made of the ice-forming molecules water, ammonia, and methane as a liquid mixture above what is thought to be a rocky core. Its atmosphere is mainly hydrogen and helium, along with methane gas that gives the planet a blue-green color.

Uranus looks like a star to the naked eye, but appears as a blue-green disk through a large telescope—Uranus was the first planet discovered by using a telescope. A flyby by the Voyager 2 space probe in 1986 provided most of the information we have about the planet, its rings, and its moons. Uranus is named after the god of the heavens in Greek and Roman mythology.

Uranus orbits the Sun at an average distance of 2,860 million km (1,780 million mi) in a period of 84 Earth years. The planet only receives about 1/400th of the sunlight that Earth does. The diameter of Uranus at its equator is 51,118 km (31,763 mi). The planet’s mass is 14.54 times greater than the mass of Earth, and its volume is 67 times greater than that of Earth. The force of gravity at the surface of Uranus is 1.17 times the force of gravity on Earth.


Hubbard, William B., B.A., Ph.D.

Professor of Planetary Sciences, University of Arizona Lunar and Planetary Laboratory. Author of "Planetary Interiors".

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