Eclipses

An eclipse (from the Greek ekleipô, “to vanish”) is an astronomical event that occurs when one celestial object moves into the shadow of another. The term is most often used to describe either a solar eclipse, when the Moon’s shadow crosses Earth’s surface, or a lunar eclipse, when the Moon moves into the shadow of Earth. However, it can also refer to such events beyond the Earth-Moon system: for example, a planet moving into the shadow cast by one of its moons, a moon passing into the shadow cast by its parent planet, or a moon passing into the shadow of another moon. An eclipse is a type of syzygy (a line up of astronomical bodies), as are transits and occultations. Eclipses are impossible on Mercury and Venus, which have no moons.