1911 Encyclopædia Britannica/Umbra

UMBRA (Lat. for shade or shadow), in astronomy, the completely dark portion of the shadow of a heavenly body, filling the space within which the sun is entirely hidden. The body being supposed spherical, the umbra is a cone circumscribing both the sun and the body that casts the shadow. The term is also given to the interior and darkest part of a sunspot. (See Sun; Eclipse.)