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reflection nebulaA bright cloud of interstellar gas and dust that lies near and somewhat to one side of a star or stellar group, usually of spectral type B2 or later. The starlight is scattered in all directions by the dust grains, the density of which is sufficient to produce a noticeable illumination of the cloud. The light scattered toward the observer is bluer than that of the illuminating star but the spectra of cloud and star are essentially the same – a continuous spectrum with absorption lines. (If there is sufficient dust in an emission nebula, it will cause the stars' absorption spectra to be added to the normal emission spectrum of the nebula.) Reflection nebulosity is characteristic of young clusters and associations; the dust is dispersed in about 100 million years. Typical reflection nebulae occur around the brighter stars of the Pleiades. See also nebula.
Collins Dictionary of Astronomy © Market House Books Ltd, 2006
reflection nebula[ri′flek·shən ‚neb·yə·lə]
A type of bright diffuse nebula composed mainly of cosmic dust; it is visible because of starlight from nearby stars or nebula stars that is scattered by the dust particles.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.