. During a lunar eclipse the initially full Moon passes through the Earth's shadow. A total lunar eclipse occurs when the entire Moon moves into the umbra. Because no portion of the Sun's surface can be seen from the umbra, it is the darkest part of the Earth's shadow. Only part of the Sun's surface is blocked out in the larger penumbra. A partial lunar eclipse occurs when the Moon's orbit takes it only partially through the umbra or only through the penumbra.
Copyright 2010, Professor Kenneth R. Lang, Tufts University