An area of darkness formed on a surface when an object intercepts the light falling on the surface from a source. In the case of a point source the shadow has a sharply defined outline. If the source has an appreciable size the shadow has two distinct regions; one of full-shadow, called the umbra, the other of half-shadow, called the penumbra.
Shadows.
- pediplain
- pedocal
- pedofacies
- pedogenesis
- pedogeomorphology
- pedology
- pedon
- pedoturbation
- Pedro I (1798–1835)
- Pedro II (1812–91)
- peduncle
- Peebles, James
- peek
- Peekskill meteorite
- Peel, Sir Robert (1788–1850)
- peel technique
- peephole optimization
- peer
- peer to peer
- peer-to-peer network
- peer-to-peer protocol
- Pegasus
- Pegasus rocket
- pegmatite
- pegmatitic