pen umbrae

penumbra

[pi-nuhm-bruh]
noun, plural penumbrae [pi-nuhm-bree] , penumbras.
1.
Astronomy.
a.
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 ).
b.
the grayish marginal portion of a sunspot. Compare umbra ( def 3b ).
2.
a shadowy, indefinite, or marginal area.

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

penumbral, penumbrous, adjective
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Based on the Random House Dictionary, © Random House, Inc. 2014.
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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

Collins English Dictionary - Complete & Unabridged 10th Edition
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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).
Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage
Science Dictionary
penumbra   (pĭ-nŭm'brə)  Pronunciation Key 
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.


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