The Penumbra reference article from the English Wikipedia on 24-Apr-2004 (provided by Fixed Reference: snapshots of Wikipedia from wikipedia.org)

Penumbra

The penumbra (Latin for mid-shadow) is the portion of a shadow that results from the source of illumination being only partially blocked. Penumbras only occur when the source of light is not a point-source. As the sun is a visible disc, solar shadows have penumbras. The penumbra part of a shadow is contrasted with the umbra part of the shadow in which the light source is completely blocked.

The penumbra is also the ring-shaped semi-bright region of a sunspot that surrounds the darker umbra.

See also: eclipse.

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