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A cloud of interstellar gas and dust that absorbs most or all of the light from luminous objects like stars behind it, appearing as an irregular dark patch. Some absorption nebulae, such as the Coalsack, are visible to the naked eye. Also called Bok globule, dark cloud, dark nebula.
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.