The third largest and the darkest moon of Uranus.
Umbriel is 16th moon in order from the planet. It is named after the "dusky
melancholy sprite" in Alexander Pope's poem "The Rape of the Lock" and is
also known as Uranus II. It was discovered by William Lassell
on October 24, 1851, at the same time as Ariel.
Umbriel's size and density are about the same as those of Ariel,
while its surface is old with little variation in the type of terrain from
one region to another. A puzzling bright ring in Umbriel's surface, initially
nicknamed the "fluorescent cheerio" and later formally named Wunda, may
be the floor of a crater but its exact nature is unknown.
| The southern hemisphere of Umbriel displays heavy
cratering in this Voyager 2 image, taken Jan. 24, 1986, from a distance
of 557,000 km (346,000 miles).
||1851, by William Lassell
|orbit semi-major axis
||266,300 km (165,510 miles)
||1,169 km (727 miles)
||0.540 km/s (1944 km/h, 1208 mph)
||4.144 days (4 days 3 hr 27 min.)