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Definition of Planetary nebula
1. Noun. A nebula that was once thought to be a star with its planets but is now thought to be a very hot star surrounded by an expanding envelope of ionized gases that emit a fluorescent glow because of intense radiation from the star.
Generic synonyms: Nebula
Definition of Planetary nebula
1. Noun. (astronomy) A nebulosity surrounding a dying star, consisting of material expelled by the star. ¹
¹ Source: wiktionary.com