World

Umbriel

Umbriel is the darkest of Uranus’s big moons, reflecting about a fifth of the light that reaches it, about 1 169 km across.

Key facts

Diameter

1 169 km

Goes round

Uranus

See it from here

Not by eye or binoculars: Umbriel is magnitude 15.1, the faintest of Uranus’s big four, so it takes a good telescope and a dark sky.

How the map draws it

Its surface is a black-and-white mosaic, tinted in a colour chosen from published descriptions · only the southern half was photographed, by Voyager 2 in 1986; the rest is left plain, not guessed · lit as a camera exposed for its own sunlight would show it · seen from far off it is a light at its computed brightness: the glow is how a camera records a point too bright to resolve.