Penumbra
PENUMBRA (Lat. paene, almost, umbra, a shadow), in astronomy, the partial shadow of a heavenly body as cast by the Sun. It is defined by the region in which the light of the Sun is partially but not wholly cut off through the interception of a dark body. (See ECLIPSE.)
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)
