Uranus was discovered by amateur astronomer William Herschel in 1781 using a six-inch telescope. The planet is tilted on its side relative to its orbit around the Sun. The north pole of Uranus sometimes points almost directly towards the Sun, and sometimes almost directly away. This means that the "daytime" and "nighttime" on Uranus can be over 40 years long!

Uranus was visited by the Voyager 2 robotic spacecraft in January 1986. Voyager 2 increased our knowledge of Uranus tremendously by providing close-up pictures of the planet and its moons and ring system.

The basics

Order (outwards from the Sun) : 7
Average distance from the Sun : 2 875 000 000 km (19.22 astronomical units)
Period of revolution (length of year) : 83.75 years
Period of rotation (length of day) : 17 hours 14 minutes at the equator
Diameter : 51 120 km at the equator
Surface gravity : 0.91 times greater than Earth’s
Composition : Possibly has an inner rocky core, overlaid with ice (frozen methane, water and ammonia) covered with an ocean of liquid hydrogen
Atmosphere : Hydrogen, helium, methane
Satellites : 22 moons, and 9 dark rings
Surface temperature : -195 degrees Celsius at the cloud tops

Appearance of surface

Probably a liquid surface under the visible cloud tops.

Appearance in Earth’s sky

Uranus is technically visible to the unaided eye, but it is near the limit of detection. It appears as an extremely faint greenish star.

Telescopic appearance

A large telescope reveals that Uranus is not a star but a tiny blue-green disk. The planet is so far away that cloud features are not visible in small telescopes.

Canadian Heritage Information Network
Australian Museums & Galleries Online, Australia; Centre of the Universe; Gemini Observatory, Hawaii; Glenbow Museum; The Manitoba Museum; National Research Council Canada; Planétarium de Montréal

© Canadian Heritage Information Network, 2003

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