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penumbra science definition
Plural penumbras penumbras or penumbrae
- 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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