Uranus, optical image. Uranus is the seventh planet from the Sun. It is a gas giant, composed mostly of hydrogen and helium with some methane. It has a diameter four times that of the Earth. The planet's blue colour is thought to result from absorption of red light by the methane in its atmosphere. Imaged by the 1M telescope at Chilescope Observatory, Cerro Pachon, Atacama, Chile on 27th November 2018.