The Jupiter Trojans are a large group of objects that share the orbit of the planet Jupiter around the Sun. Relative to Jupiter, each Trojan librates around one of the planet's two Lagrangian points of stability, L4 and L5, that respectively lie 60° ahead of and behind the planet in its orbit. Trojan asteroids are distributed in two elongated, curved regions around these Lagrangian points with an average semi-major axis of about 5.2 AU. The first Trojan, 588 Achilles, was discovered in 1906 by the German astronomer Max Wolf. A total of 2,909 Jupiter Trojans have been found as of January 2009. The name "Trojans" derives from the fact that, by convention, they each are named after a mythological figure from the Trojan War. The total number of Jupiter Trojans larger than 1 km is believed to be about 1 million, approximately equal to the number of asteroids larger than 1 km in the main asteroid belt Like main belt asteroids, Trojans form families. Jupiter Trojans are dark bodies with reddish, featureless spectra. No firm evidence of the presence of water, organic matter or other chemical compounds has been obtained. The Trojans' densities (as measured by studying binaries or rotational lightcurves) vary from 0.8 to 2.5 g·cm−3. Trojans are thought to have been captured into their orbits during the early stages of the Solar System's formation or slightly later, during the migration of giant planets.

Read the rest of this article: http://en.wikipedia.org/wiki/Jupiter_Trojan

_______________________________ Today's selected anniversaries:

1153:

Malcolm IV became King of Scotland at the age of twelve. http://en.wikipedia.org/wiki/Malcolm_IV_of_Scotland

1703:

Russian Tsar Peter I founded Saint Petersburg after reconquering the Ingrian land from Sweden during the Great Northern War. http://en.wikipedia.org/wiki/History_of_Saint_Petersburg

1937:

The Golden Gate Bridge , at the time the world's longest suspension bridge span, connecting the San Francisco to Marin County, California, opened. http://en.wikipedia.org/wiki/Golden_Gate_Bridge

1942:

Czech resistance fighters in Nazi-occupied Prague ambushed and mortally wounded Reinhard Heydrich, the chief of Reich Security Main Office and the Protector of Bohemia and Moravia. http://en.wikipedia.org/wiki/Operation_Anthropoid

1995:

Actor Christopher Reeve suffered a cervical spinal injury after being thrown from his horse during the cross country portion of an eventing competition held in Culpeper, Virginia, paralyzing him from the neck down. http://en.wikipedia.org/wiki/Christopher_Reeve

_____________________________ Wiktionary's word of the day:

incubus (n): 1. An evil spirit supposed to oppress people while asleep, especially to have sex with women as they sleep. 2. A feeling of oppression during sleep; night terrors, a nightmare. 3. Any oppressive thing or person; a burden http://en.wiktionary.org/wiki/incubus

___________________________ Wikiquote quote of the day:

The more clearly we can focus our attention on the wonders and realities of the universe about us the less taste we shall have for the destruction of our race. Wonder and humility are wholesome emotions, and they do not exist side by side with a lust for destruction. --Rachel Carson http://en.wikiquote.org/wiki/Rachel_Carson