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noun, Astronomy.
a bright diffuse nebula that emits light as a result of ionization of its gas atoms by ultraviolet radiation, as the Orion Nebula, planetary nebulae, and supernova remnants, as the Crab Nebula.
a type of nebula that emits visible radiation See nebula
emission nebula
A nebula that absorbs ionizing ultraviolet radiation from nearby hot stars or star remnants and reemits it as visible light. HII regions, planetary nebulae, and nebulae created by the explosion of supernovae are different kinds of emission nebulae. See more at nebula.


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  • Emissions trading

    noun an approach used to control pollution by providing economic incentives for achieving reductions in the emissions of pollutants; also called cap-and-trade Examples The fact that the permits in emissions trading have value as an item to be sold or traded gives the owner an incentive to reduce their emissions.

  • Emissive

    [ih-mis-iv] /ɪˈmɪs ɪv/ adjective 1. serving to emit. 2. pertaining to .

  • Emissivity

    [em-uh-siv-i-tee, ee-muh-] /ˌɛm əˈsɪv ɪ ti, ˈi mə-/ noun, Thermodynamics. 1. the ability of a surface to emit radiant energy compared to that of a black body at the same temperature and with the same area. /ɪmɪˈsɪvɪtɪ; ˌɛm-/ noun 1. a measure of the ability of a surface to radiate energy; the ratio of the […]

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