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.
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How to use planetary nebula in a sentence
While about half its mass will flood out, the rest will crush together at the very center of the planetary nebula.
A star has actually, under our eyes, become a planetary nebula, and the cycle of which he gave the first terms is complete.Sir William Herschel: His Life and Works | Edward Singleton Holden
Its visual appearance in the great telescope was now also that of a planetary nebula.Pleasures of the telescope | Garrett Serviss
For a glance at a planetary nebula we may turn with the five-inch to No. 4234.Pleasures of the telescope | Garrett Serviss
British Dictionary definitions for planetary nebula
an expanding shell of gas surrounding a dying star, formed from matter ejected from the star's outer layers; the gas is ionized by the remaining hot stellar core, emitting light in the process
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
Scientific definitions for planetary nebula
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.
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