pen umbra

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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Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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