penumbra(redirected from geometric unsharpness)
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penumbra(pĭnŭm`brə): see eclipseeclipse
[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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the space between regions of total shadow and total light formed behind an opaque body illuminated by a light source whose dimensions are comparable both with the dimensions
of the body and with the distance from the light source to the body (see Figure 1). Only part of the light source is visible in the penumbra; the light source is not visible in the umbra and is completely visible in the region of total light. The point of observation of a partial solar eclipse is within the penumbra formed by the moon as illuminated by the sun.