- noun a region or cloud of interstellar dust and gas
- Latin for Cloud. The term was originally applied to any non-point source of light from outside the solar system, but is now no longer used to describe galaxies. A wide range of types of nebulae are recognised, including dark and bright types, some dominated by gas and others in which dust is a major component. Dark nebulae are seen as dark outlines against bright objects – the Coalsack being a prime example. Among bright nebulae are reflection nebulae which shine by light reflected from other objects, emission nebulae which glow, usually from emissions from hot, young stars, and planetary nebulae, which are expanding gas bubbles resulting from nova explosions. The solar nebula is the term for the mass from which the Sun and the rest of the solar system have condensed. The types of nebula merge into each other and a given nebula can have parts which absorb radiation, and others which reflect or retransmit it.
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