penumbral

noun, plural pe·num·brae

[-bree] , pe·num·bras.

Astronomy.

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 ).

the grayish marginal portion of a sunspot. Compare umbra ( def 3b ).

a shadowy, indefinite, or marginal area.

Origin:
1660–70; < Neo-Latin, equivalent to Latin paen- pen- + umbra shade

Related forms

pe·num·bral, pe·num·brous, adjective

Dictionary.com Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2013.
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World English Dictionary

penumbra (pɪˈnʌmbrə)

—n , pl -brae, -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

[C17: via New Latin from Latin paene almost + umbra shadow]

pe'numbral

—*adj*

pe'numbrous

—*adj*

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penumbra (pɪˈnʌmbrə)

—n , pl -brae, -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

[C17: via New Latin from Latin paene almost + umbra shadow]

pe'numbral

—*adj*

pe'numbrous

—*adj*

Collins English Dictionary - Complete & Unabridged 10th Edition
2009 © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009
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Etymonline

Word Origin & History

penumbra

1666, from Mod.L. penumbra "partial shadow outside the complete shadow of an eclipse," coined 1604 by Kepler from L. pæne "almost" + umbra "shadow" (see umbrage).

American Heritage

Science Dictionary

penumbra

(pĭ-nŭm'brə) Pronunciation Key
Plural penumbras or penumbrae (pĭ-nŭm'brē)

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.
The grayish outer part of a sunspot. Compare umbra.

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