An eclipse is an astronomical event that occurs when one celestial object moves into the shadow of another. The term is derived from the ancient Greek noun ἔκλειψις (ékleipsis), which is derived from the verb ἐκλείπω (ekleípō), "to cease to exist," a combination of prefix εκ- (ek-), from preposition εκ, εξ (ek, ex), "out," and of verb λείπω (leípō), "to be absent".  When an eclipse occurs within a stellar system, such as the solar system, it forms a type of syzygy—the alignment of three or more celestial bodies in the same gravitational system along a straight line.
The term eclipse is most often used to describe either a solar eclipse, when the Moon's shadow crosses the 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 host planet, or a moon passing into the shadow of another moon. A binary star system can also produce eclipses if the plane of their orbit intersects the position of the observer.
- A Catalogue of Eclipse Cycles
- Search 5,000 years of eclipses
- NASA eclipse home page
- International Astronomical Union's Working Group on Solar Eclipses
- Mark's eclipse chasing website
- Interactive eclipse maps site