PLANETS & MOONS A  B  C  D  E  F  G  H  I  J  K  L  M  N  O  P  Q  R  S  T  U  V  W  X  Y  Z                    HOME ABOUT CATEGORIES SITE MAP COPYRIGHT ADVERTISE CONTACT entire Web this site Umbriel 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). 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. Discovery 1851, by William Lassell Orbit semi-major axis 266,300 km (165,510 miles) Diameter 1,169 km (727 miles) Mean density 1.40 g/cm3 Escape velocity 0.540 km/s (1944 km/h, 1208 mph) Orbital period 4.144 days (4 days 3 hr 27 min.) Axial period 4.144 days Orbital eccentricity 0.0039 Orbital inclination 0.36° Visual albedo 0.21 Related entry    • Uranus, moons Related category    • PLANETS AND MOONS Also on this site: Encyclopedia of Alternative Energy & Sustainable Living Encyclopedia of History Transport Concepts & Designs (partner site) BACK TO TOP