Voyager 2 composite colour image of Umbriel, a Uranian satellite, taken on Jan 23, 1986 with separate violet and clear filters. The spacecraft was 1.04 million kilometres (650,000 miles) from Umbriel & heading for the closest encounter with Uranus on the 24th January. Umbriel, the darkest of Uranus's five major satellites, has a diameter of 1200km, & orbits Uranus at a radius of 267,000km. Umbriel is characterised by a dark surface with small brightness variations. This picture shows that the surface is covered by impact craters. The brightest spot on it is seen here as a bright ring (photo top right) but its geological significance is not yet known. NASA 5x4 number 86 HC 79