Uranus, the seventh planet from the sun. Uranus was the first planet to be discovered with a telescope, Mercury, Venus, Mars, Jupiter, and Saturn being readily visible to the unaided eye. Uranus was the first planet to be discovered since ancient times. When Sir William Herschel sighted Uranus in 1781, he at first mistook it for a comet. Under good viewing conditions, it is just visible to a person of keen eyesight. German astronomer Johann E. Bode named Uranus after a sky god in Greek mythology. Uranus and Neptune are similar in size and appearance. In the late 1970s, astronomers discovered that Uranus was encircled by a series of nine narrow rings. Unlike the rings of Saturn, these rings are dark and are probably composed of particles of rock.

Uranus at a glance
Distance from the sun: Shortest--1,703,360,000 mi (2,741,300,000 km); Greatest--1,866,360,000 mi (3,003,620,000 km); Average--1,784,860,000 mi (2,872,460,000 km).
Distance from Earth: Shortest--1,604,300,000 mi (2,581,900,000 km); Greatest--1,961,900,000 mi (3,157,300,000 km).
Diameter at equator: 31,763 mi (51,118 km).
Length of year: 84 Earth years.
Rotation period: 17 hours 14 minutes.
Temperature: 355 °F (215 °C).
Atmosphere: Hydrogen, helium, methane.
Number of satellites: At least 27.