Voyager 2 colour composite image of Uranus, taken on January 25, 1986, as the spacecraft left the planet behind & set off towards Neptune. The thin crescent of Uranus, seen here, shows a pale blue- green colour. This results from the presence of methane in the planet's atmosphere, which absorbs red wavelengths of light, leaving a predominantly blueish hue. The crescent tends to become white at its extreme edge due to the presence of a high- altitude haze.