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See more synonyms for penumbra on Thesaurus.com
noun, plural pe·num·brae [pi-nuhm-bree] /pɪˈnʌm bri/, pe·num·bras.
  1. Astronomy.
    1. the partial or imperfect shadow outside the complete shadow of an opaque body, as a planet, where the light from the source of illumination is only partly cut off.Compare umbra(def 3a).
    2. the grayish marginal portion of a sunspot.Compare umbra(def 3b).
  2. a shadowy, indefinite, or marginal area.
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Origin of penumbra

1660–70; < New Latin, equivalent to Latin paen- pen- + umbra shade
Related formspe·num·bral, pe·num·brous, adjective
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

Related Words


Examples from the Web for penumbra

Contemporary Examples

Historical Examples

  • This is the entrance into the “penumbra” (or “Partial shade”).

    The Story of Eclipses

    George Chambers

  • The idea of change is there, I am willing to grant, but it is hidden in the penumbra.

    Creative Evolution

    Henri Bergson

  • The penumbra will last quite a long time yet, but it will gradually get fainter and fainter.

    Pharaoh's Broker

    Ellsworth Douglass

  • Two tears, phosphorescent in the penumbra, rolled from the eyes of the painter.

    A Chambermaid's Diary

    Octave Mirbeau

  • Each spot is quite sharply divided into an umbra and a penumbra.

    Astronomy for Young Folks

    Isabel Martin Lewis

British Dictionary definitions for penumbra


noun plural -brae (-briː) or -bras
  1. a fringe region of half shadow resulting from the partial obstruction of light by an opaque object
  2. astronomy the lighter and outer region of a sunspot
  3. painting the point or area in which light and shade blend
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Compare umbra
Derived Formspenumbral or penumbrous, adjective

Word Origin

C17: via New Latin from Latin paene almost + umbra shadow
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for penumbra


1660s, from Modern Latin penumbra "partial shadow outside the complete shadow of an eclipse," coined 1604 by Kepler from Latin pæne "almost" + umbra "shadow" (see umbrage). Related: Penumbral.

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Online Etymology Dictionary, © 2010 Douglas Harper

penumbra in Science


Plural penumbras penumbrae (pĭ-nŭmbrē)
  1. A partial shadow between regions of full shadow (the umbra) and full illumination, especially as cast by Earth, the Moon, or another body during an eclipse. During a partial lunar eclipse, a portion of the Moon's disk remains within the penumbra of Earth's shadow while the rest is darkened by the umbra. See Note at eclipse.
  2. The grayish outer part of a sunspot. Compare umbra.
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The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.