Lunar eclipse. Artwork showing the mechanics of a lunar eclipse. During a lunar eclipse, the Moon passes into the shadow of the Earth, causing its visible face to darken. It does not disappear completely as some light is refracted onto it by the Earth's atmosphere. The Earth's shadow comprises a dark central umbra surrounded by the lighter penumbra. A total lunar eclipse can only occur at Full Moon, when the Earth lies directly between the Moon and the Sun. It does not occur every Full Moon as the orbital planes of the Earth and Moon are slightly inclined with respect to each other. A lunar eclipse is visible from everywhere on the night side of the Earth.