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[pi-nuhm-bruh] /pɪˈnʌm brə/
noun, plural penumbrae
[pi-nuhm-bree] /pɪˈnʌm bri/ (Show IPA),
  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).
a shadowy, indefinite, or marginal area.
Origin of penumbra
1660-70; < New Latin, equivalent to Latin paen- pen- + umbra shade
Related forms
penumbral, penumbrous, adjective Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2018.
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Examples from the Web for penumbra
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
  • To-day, even, we can see the Dawn: the penumbra is vanishing.

  • Now I will try and explain to you what the penumbra is and how it is produced.

  • And Porter was still working away, looking ghostly in the penumbra.

    A Top-Floor Idyl

    George van Schaick
  • Thus they were in a little island of pink light surrounded by penumbra.

    A Bed of Roses W. L. George
  • The answer is not yet made, the oracle has not spoken, and we must not invade the penumbra of genius.

    Brave Men and Women O.E. Fuller
British Dictionary definitions for penumbra


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

Online Etymology Dictionary, © 2010 Douglas Harper
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penumbra in Science
Plural penumbras or penumbrae (pĭ-nŭm'brē)
  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.

The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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