umbra
1. a region of complete shadow resulting from the total obstruction of light by an opaque object, esp the shadow cast by the moon onto the earth during a solar eclipse
2. the darker inner region of a sunspot
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005
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Umbral and penumbral regions of a shadow
umbra
(um -bră) 1. The dark inner region of a shadow cast by an object illuminated by a light of finite size rather than a pinpoint of light. The less dark outer region of the shadow is the penumbra (see illustration). The source of light is totally obscured to someone in the umbral region but only partly obscured in the penumbral region. See eclipse.
2. See sunspots.
Collins Dictionary of Astronomy © Market House Books Ltd, 2006
umbra
[′əm·brə] (astronomy)
The dark, central region of a sunspot.
(optics)
That portion of a shadow which is screened from light rays emanating from any part of an extended source.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.