UMBRA

that part of a shadow area over which all light from a given source is excluded. The shadow from a point source of illumination is essentially all umbra, but that from a source of some size (as from the Sun) consists of a small umbra and a much larger partial shadow called the penumbra (q.v.). Thus, in an eclipse of the Sun, the regions of umbra are those experiencing total eclipse and those of penumbra, partial eclipse. The term is also used for the darkest inner portion of a sunspot.