1910–1911
Britannica 11th
Encyclopaedia Britannica · 11th edition
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.)
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- Vol. 27, pp. 576-576