umbra(redirected from umbras)
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Related to umbras: umbral
[Gr.,=failing], in astronomy, partial or total obscuring of one celestial body by the shadow of another. Best known are the lunar eclipses, which occur when the earth blocks the sun's light from the moon, and solar eclipses, occurring when the moon blocks the sun's light
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dark, usually irregularly shaped spots on the sun's surface that are actually solar magnetic storms. The spots are darker because the temperature of the spots is lower than that of the surrounding photosphere (the visible surface of the sun).
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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
The dark, central region of a sunspot.
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.
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