Penumbra
From Freepedia
Image:Umbra01.gif 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 part of the penumbra where an annular eclipse is visible is called the antumbra.
Also, the penumbra is the lighter, fuzzier outer edge of a shadow. The shadow is darkest at the umbra, near the object, and weakest at the penumbra, at the edge.
Other meanings
- The penumbra is also the ring-shaped semi-bright region of a sunspot that surrounds the darker umbra.
- The Penumbra is also a region in the Umbra, the spirit world of the World of Darkness line of role-playing games.
- An area in which something exists to a lesser or uncertain degree: "The 4th Amendment has a penumbra where privacy is protected from governmental intrusion.”
—Joseph A. Califano, Jr.
