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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. 2015.
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British Dictionary definitions for penumbral


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
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Word Origin and History for penumbral



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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penumbral 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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