Uranus

The seventh planet from the Sun

Uranus lies on its side. Its axis is tipped 98° from its orbit, so over its 84-year year each pole has about 42 years of daylight and then 42 of night. The Sun crossed its equator at the end of 2007; it now stands high over the north pole, and will be highest at the solstice of 2030.

An ice giant four times Earth's width, it is made mostly of water, methane and ammonia around a small rocky core, under an atmosphere of hydrogen and helium whose methane gives it its pale blue-green colour. It was the first planet found with a telescope, by William Herschel in 1781, and only one probe has been there: Voyager 2, which flew past on 24 January 1986 and saw an almost featureless disc.