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Umbriel(ŭm`brēĕl'), in astronomy, one of the moons, or natural satellites, of UranusUranus
, in astronomy, 7th planet from the sun, at a mean distance of 1.78 billion mi (2.87 billion km), with an orbit lying between those of Saturn and Neptune; its period of revolution is slightly more than 84 years.
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Umbriel(um -bree-ĕl) A satellite of Uranus, discovered in 1851 by William Lassell. Photographed by Voyager 2 in 1986, it is very dark with an albedo of only 0.18. It is heavily cratered, its most prominent feature being Skyund, a crater 100 km in diameter with a bright central peak. See also Uranus' satellites; Table 2, backmatter.
a satellite of the planet Uranus. Umbriel has a diameter of about 1,000 km and is at a mean distance of 267,000 km from the center of the planet. The satellite was discovered in 1851 by W. Lassell. The orbital plane of Umbriel is nearly perpendicular to the orbital plane of Uranus.