Lunar eclipse. Diagram showing the positions of the Earth, Moon and Sun during a lunar eclipse. Total lunar eclipses occur when the Earth moves between the Sun and the Moon, and casts its shadow (darker blue, umbra) across the surface of the Moon. As seen here, the cone of Earth's shadow is larger than the Moon's width at the same point, and because of this, totality can last up to 107 minutes. Lunar eclipses occur only at full Moon, and then only when the Earth and full Moon are correctly aligned (about 2-3 times a year). They do not occur every full Moon as the Moon's orbit is slightly inclined to the Earth's orbit around the Sun. Penumbral lunar eclipses occur when the Moon, Earth and Sun are imperfectly aligned and the Moon is in the Earth's penumbra (lighter blue shadow). During a penumbral lunar eclipse the Moon is illuminated by sunlight directly from the Sun and from sunlight refracted through the Earth's atmosphere.