An H II region is a cloud of glowing gas, sometimes several hundred light years across, in which star formation is taking place. Young, hot, blue stars which have formed from the gas emit copious amounts of ultraviolet light, ionising the nebula surrounding them. H II regions may give birth to thousands of stars over a period of several million years. In the end, supernova explosions and strong stellar winds from the most massive stars in the resulting star cluster will evaporate the gases of the H II region, leaving behind a cluster such as the Pleiades. H II (pronounced "H two") regions are named for the large amount of ionised atomic hydrogen they contain, referred to as H II by astronomers (H I being neutral atomic hydrogen, and H2 being molecular hydrogen). H II regions can be seen out to considerable distances in the universe, and study of extragalactic H II regions is important in determining the distance and chemical composition of other galaxies.
Read the rest of this article: http://en.wikipedia.org/wiki/H_II_region
_______________________________ Today's selected anniversaries:
Today: Candlemas (Western Christianity); Groundhog Day in Canada and the United States.
962: Pope John XII crowned Otto the Great as Holy Roman Emperor, the first in nearly 40 years.
1848: The Mexican-American War ended with the signing of the Treaty of Guadalupe Hidalgo, granting the United States the Mexican Cession.
1925: Medical supplies to combat an outbreak of diphtheria reached Nome, Alaska on dog sleds, inspiring the annual Iditarod race across Alaska.
1943: The Battle of Stalingrad concluded, with 91,000 tired and starving German soldiers taken captive by the Red Army.
1990: President F.W. de Klerk declared the end of Apartheid in South Africa.
_____________________ Wikiquote of the day:
"There ain't no such thing as a free lunch" -- American proverb (http://en.wikiquote.org/wiki/American_proverbs)