Lunar eclipse geometry, artwork. Lunar eclipses occur when the Moon passes into the shadow of the Earth. The lunar day is interrupted as the Sun, as seen from the Moon, is blocked by the Earth. From the Earth, the light of the Full Moon darkens but does not disappear entirely since some sunlight is refracted onto it by the Earth's atmosphere. The shadow of the Earth consists of a dark central umbra (causing total eclipses) surrounded by a lighter penumbra (partial eclipses). Total lunar eclipses can last nearly 2 hours. Lunar eclipses only occur at Full Moon and only if the Earth and Moon are correctly aligned, which only happens 2-3 times a year.