planetary nebula

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.
[1850-55; so named for its resemblance to the planets Uranus and Neptune]

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Any of a class of bright nebulae that may somewhat resemble planets when viewed through a small telescope but are, in fact, expanding shells of luminous gas around dying stars.

A planetary nebula is the outer envelope shed by a red giant star not massive enough to become a supernova. Instead, the star's intensely hot core becomes exposed (see white dwarf star) and ionizes the surrounding shell of gas, which is expanding at tens of miles per second.

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 any of a class of bright nebulae (nebula) that are expanding shells of luminous gas expelled by dying stars (star). Observed telescopically, they have a relatively round, compact appearance rather than the chaotic, patchy shapes of other nebulae—hence their name, which was given because of their resemblance to planetary disks when viewed with the instruments of the late 1700s, when the first planetary nebulae were discovered.

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Universalium. 2010.

Look at other dictionaries:

  • Planetary nebula — Planetary Plan et*a*ry, a. [Cf. L. planetarius an astrologer, F. plan[ e]taire planetary. See {Planet}.] 1. Of or pertaining to the planets; as, planetary inhabitants; planetary motions; planetary year. [1913 Webster] 2. Consisting of planets; as …   The Collaborative International Dictionary of English

  • planetary nebula — n. [from its resemblance, when viewed through a telescope, to a PLANET] a glowing, expanding nebula that forms around a collapsing star …   English World dictionary

  • Planetary nebula — A planetary nebula is an emission nebula consisting of a glowing shell of gas and plasma formed by certain types of stars when they die. The name originated in the 18th century because of their similarity in appearance to giant planets when… …   Wikipedia

  • Planetary Nebula M2-9 — For other uses of Butterfly Nebula , see Butterfly Nebula (disambiguation). Minkowski 2 9 (M2 9) Observation data (Epoch J2000) …   Wikipedia

  • planetary nebula — 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 • Hypernyms:… …   Useful english dictionary

  • planetary nebula — noun Date: 1785 a usually compact luminous ring shaped nebula that is composed of matter which has been ejected from a hot star at its center …   New Collegiate Dictionary

  • planetary nebula — noun Astronomy a ring shaped nebula formed by an expanding shell of gas round an ageing star …   English new terms dictionary

  • planetary nebula — noun A nebulosity surrounding a dying star, consisting of material expelled by the star. Syn: PN …   Wiktionary

  • planetary nebula — plan′etary neb′ula n. astron. an expanding shell of thin ionized gas that is ejected from and surrounds a hot, dying star • Etymology: 1775–85 …   From formal English to slang

  • planetary nebula — /plænətri ˈnɛbjələ/ (say planuhtree nebyuhluh) noun shells of gas ejected from certain very hot stars …   Australian English dictionary

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