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planetary nebula

 - 3 dictionary results

planetary nebula

 
Use planetary nebula in a Sentence
–noun Astronomy.
an expanding shell of thin ionized gas that is ejected from and surrounds a hot, dying star of about the same mass as the sun; the gas absorbs ultraviolet radiation from the central star and reemits it as visible light by the process of fluorescence.
Origin:
1850–55; so named for its resemblance to the planets Uranus and Neptune
Dictionary.com Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2009.
Cite This Source Link To planetary nebula
planetary nebula  
n.  

  1. A nebula, such as the Ring Nebula, consisting of a hot, blue-white, central star surrounded by an envelope of expanding gas.

  2. A low-mass star in a later stage of its evolution during which the star ejects its outer layers, often in an expanding spherical shell, exposing the hot stellar core.

The American Heritage® Dictionary of the English Language, Fourth Edition
Copyright © 2009 by Houghton Mifflin Company.
Published by Houghton Mifflin Company. All rights reserved.
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Science Dictionary
planetary nebula   (plān'ĭ-těr'ē)  Pronunciation Key 
A nebula consisting of a rapidly expanding shell of glowing gas, mostly hydrogen, ejected from a red giant upon its collapse into a white dwarf. Ultraviolet radiation from the hot, luminous white dwarf ionizes the expanding gas and causes it to glow. The nebula disappears once the cooling dwarf can no longer ionize it, and its material eventually returns to the interstellar medium. See more at white dwarf.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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