Illustration of Uranus, its rings and 18 of its 27 known moons. 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. Its rings are fainter than those of Saturn, and are thought to be composed of particles coated in dark, sooty material. Uranus is unique among the planets of the solar system in having a tilted rotation axis that is close to the main solar system plane in which most planets move.