emission nebula

emission nebula

noun Astronomy.
a bright diffuse nebula that emits light as a result of ionization of its gas atoms by ultraviolet radiation, as the Orion Nebula, planetary nebulae, and supernova remnants, as the crab Nebula.
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Collins
World English Dictionary
emission nebula
 
n
See nebula a type of nebula that emits visible radiation

Collins English Dictionary - Complete & Unabridged 10th Edition
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American Heritage
Science Dictionary
emission nebula   (ĭ-mĭsh'ən)  Pronunciation Key 
A nebula that absorbs ionizing ultraviolet radiation from nearby hot stars or star remnants and reemits it as visible light. HII regions, planetary nebulae, and nebulae created by the explosion of supernovae are different kinds of emission nebulae. See more at nebula.
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Encyclopedia Britannica
Encyclopedia

emission nebula

in astronomy, a bright, diffuse light sometimes associated with supernova remnants or with stars whose temperatures exceed 20,000 K. The excitation process necessary to provide observed optical and radio energies in such gaseous regions was long an astronomical puzzle. Spectral and polarization studies of the 1950s suggested that their luminosity largely results from synchrotron radiation-energy from electrons accelerated in a magnetic field, as seen in certain particle accelerators.

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
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