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Old 10-04-2012, 02:29 PM   #97
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Lightbulb Star

Artist's conception of the birth of a star within a dense molecular cloud. NASA image...Stella is the Latin and Italian for "star".

A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth. Other stars are visible from Earth during the night, when they are not obscured by atmospheric phenomena, appearing as a multitude of fixed luminous points because of their immense distance.Historically, the most prominent stars on the celestial sphere were grouped together into constellations and asterisms, and the brightest stars gained proper names.

A molecular cloud, sometimes called a stellar nursery if star formation is occurring within, is a type of interstellar cloud whose density and size permits the formation of molecules, most commonly molecular hydrogen (H2).Isolated gravitationally bound small molecular clouds with masses less than a few hundred times the mass of the Sun are called Bok globules.Bok globules are dark clouds of dense cosmic dust and gas in which star formation sometimes takes place...Bok globules that are blasted by nearby stars exhibit fragmentation of materials to produce a tail.

In 1984 IRAS identified a new type of diffuse molecular cloud. These were diffuse filamentary clouds that are visible at high galactic latitudes (looking out of the plane of the galactic disc). The galactic coordinate system (GCS) is a celestial coordinate system which is centered on the Sun and is aligned with the apparent center of the Milky Way galaxy...

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