Umbriel is a moon of Uranus discovered together with Ariel on October 24, 1851, by William Lassell. It was named after a character in Alexander Pope's poem The Rape of the Lock. Umbriel consists mainly of ice with a substantial fraction of rock, and may be differentiated into a rocky core and an icy mantle. The surface is the darkest among Uranian moons, and appears to have been shaped primarily by impacts. However, the presence of canyons suggests early endogenic processes, and the moon may have undergone an early endogenically driven resurfacing event that obliterated its older surface. Covered by numerous impact craters reaching 210 km (130 mi) in diameter, Umbriel is the second most heavily cratered satellite of Uranus after Oberon. The most prominent surface feature on it is a ring of bright material on the floor of Wunda crater. This moon, like all moons of Uranus, probably formed from an accretion disk that surrounded the planet just after its formation. The Uranian system has been studied up close only once: by the spacecraft Voyager 2 in January 1986. It took several images of Umbriel, which allowed mapping of about 40% of the moon’s surface.

Read the rest of this article: http://en.wikipedia.org/wiki/Umbriel_%28moon%29

_______________________________ Today's selected anniversaries:

1860:

The Pony Express, a mail service that became the most direct means of long distance communication to the American West, began operation. http://en.wikipedia.org/wiki/Pony_Express

1888:

The first of eleven unsolved brutal murders of women committed in or near the impoverished Whitechapel district in the East End of London, occurred. http://en.wikipedia.org/wiki/Whitechapel_murders

1922:

Joseph Stalin became the first General Secretary of the Communist Party of the Soviet Union. http://en.wikipedia.org/wiki/Joseph_Stalin

1948:

An uprising began on Jeju Island, eventually leading to the deaths of between 14,000 and 30,000 individuals due to fighting between its various factions, and the violent suppression of the rebellion by the South Korean army. http://en.wikipedia.org/wiki/Jeju_Uprising

1973:

On a New York City street, Motorola researcher Martin Cooper made the first public call on a handheld mobile phone. http://en.wikipedia.org/wiki/Martin_Cooper_%28inventor%29

_____________________________ Wiktionary's word of the day:

potentate (n): A powerful leader; a monarch, ruler http://en.wiktionary.org/wiki/potentate

___________________________ Wikiquote quote of the day:

I am only one,

But still I am one. I cannot do everything, But still I can do something;

And because I cannot do everything I will not refuse to do the something that I can do. --Edward Everett Hale http://en.wikiquote.org/wiki/Edward_Everett_Hale