Umbriel (moon)

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Umbriel ("UM bree uhl") is a moon of Uranus discovered in 1851 by William Lassell. It was discovered at the same time as Ariel.

The name "Umbriel" and the names of all four satellites of Uranus then known were suggested by John Herschel in 1852 at the request of Lassell[1] (http://adsabs.harvard.edu//full/seri/AN.../0034//0000169.000.html). Lassell had earlier endorsed Herschel's 1847 naming scheme for the seven then-known satellites of Saturn and had named his newly-discovered eighth satellite Hyperion in accordance with Herschel's naming scheme in 1848.

Physical characteristics

Umbriel's surface is the darkest of the Uranian moons, and it is also the least geologically active. It is mostly composed of water ice, with the balance made up of silicate rock and methane ice. Most of its methane ice is on its surface. Coincidentally, Umbriel's dark colour suits its name: Umbriel is the 'dusky melancholy sprite' in Alexander Pope's The Rape of the Lock, and the name suggests the Latin umbra, shadow.

Umbriel's most prominent feature is Wunda, a large ring of bright material (see picture). Wunda is presumably some kind of crater, but its exact nature is mysterious.

See also: List of craters on Umbriel

Data for Umbriel:

• Mean Diameter: 1169.4 km
• Surface Area: 4,300,000 km²
• Orbital radius: 266,000 km
• Rotation period: 4.14 days
• Orbital period: 4.14 days

External links

• William Lassell, Astronomical Journal 2 (1851) 70 (http://adsabs.harvard.edu//full/seri/AJ.../0002//0000070.000.html)
• AN, 33 (1852) 257/258 (http://adsabs.harvard.edu//full/seri/AN.../0033//0000136.000.html)
• AN, 34 (1852) 325/326 (http://adsabs.harvard.edu//full/seri/AN.../0034//0000169.000.html)

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