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Penumbras

 [pi-nuhm-bruh]  

pe·num·bra

   [pi-nuhm-bruh]
noun, plural pe·num·brae  [-bree] , pe·num·bras.
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

Related forms
pe·num·bral, pe·num·brous, adjective
Dictionary.com Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2012.
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Penumbras is always a great word to know.
So is bezoar. Does it mean:
a calculus or concretion found in the stomach or intestines of certain animals, esp. ruminants, formerly reputed to be an effective remedy for poison.
an extraordinary or unusual thing, person, or event; an exceptional example or instance.
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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.


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