Related Directory Categories
- Bastia Umbra (72)
- Affari e Economia (52)
- Servizi (18)
- Produttori (16)
- Turismo (8)
- Nocera Umbra (8)
- Negozi (7)
- Grossisti e Distributori (6)
- Arte e Intrattenimento (6)
- Società e Cultura (2)
Sources
Help build the largest human-edited directory on the web.
Submit a site - Become an editor
Wikipedia. Licensed under the GNU Free Documentation License.
Are you an expert in this subject? Join the discussion and share your knowledge at Wikipedia.org.
Umbra
From Wikipedia, the free encyclopedia
- For other uses of the word "umbra", see Umbra (disambiguation).
- For other uses of the word "penumbra", see Penumbra (disambiguation).
 |
This article does not cite any references or sources. (December 2007) Please help improve this article by adding citations to reliable sources. Unverifiable material may be challenged and removed. |
The umbra (Latin: "shadow") is the darkest part of a shadow. From within the umbra, the source of light is completely blocked by the object causing the shadow. This contrasts with the penumbra, where the light source is only partially blocked and there is only a partial shadow.
Penumbras occur only when the source of light is not a point source. As the sun is a visible disc, solar shadows have penumbras.
The part of the penumbra in which an annular eclipse is visible is called the antumbra. In an annular eclipse, the moon's shadow is not long enough to reach the Earth and result in a total solar eclipse. In such an eclipse, the moon's apparent diameter (as seen from the Earth's surface) is not large enough to completely obscure the sun, and at maximum eclipse, the moon appears to be surrounded by a ring, or annulus, of light. The location on Earth where the ring can be seen is also the location of the antumbra. Although the antumbra may be referred to as a "negative shadow", it is nevertheless darker than the penumbra, just like the umbra is in a total eclipse. However, whereas the umbra is completely devoid of sunlight, the antumbra is not because of the remaining ring.