Uranus

Uranus is the seventh planet from the sun. It is sixth in size and just visible to the human eye. It was discovered by accident by the British astronomer William Herschel in the 18th century.

Uranus has a diameter of over 50,000 km - about 4 times that of the Earth and it is 3 billion km away from the sun. It takes Uranus 84 years for one single orbit around the sun and 17 hours for one rotation around its axis. The unusual thing about Uranus is that its poles are pointed directly at the sun. This means that it orbits the sun on its side. Each pole gets 42 years of sunlight and then 42 years of darkness.

Uranus belongs to the "gas giants". Its atmosphere consists mostly of hydrogen and helium and a bit of methane, which gives the planet a bluish-green color. The surface of Uranus is probably made up of frozen gas. Underneath this crust, there is a layer of poisonous water. The core is ice and rock.

In 1977 an American astronomer discovered that Uranus also has a system of rings. 10 of the 17 moons were discovered when Voyager 2 flew by the planet in 1986.

Size of Uranus compared to the Earth
Image: NASA (image modified by Jcpag2012),
Public domain, via Wikimedia Commons