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Meaning of planetary nebula

plan'etary neb'ula

Pronunciation: [key]
— Astron. Astron.
  1. 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.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.
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