Definition of planetary nebula in English:

planetary nebula

Syllabification: plan·e·tar·y neb·u·la

noun

Astronomy
A ring-shaped nebula formed by an expanding shell of gas around an aging star.
More example sentences
  • Astronomers call such an object a planetary nebula, because its round shape resembles that of a planet when viewed with a small telescope.
  • The Boomerang Nebula is a young planetary nebula and the coldest object found in the Universe so far.
  • Until recently, it was thought that shells around planetary nebulae were a rare phenomenon.

Definition of planetary nebula in:

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Word of the day internecine
Pronunciation: ˌɪntəˈniːsʌɪn
adjective
destructive to both sides in a conflict