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), from verb ἐκλείπω (ekleípō), "to leave behind," a combination of prefix ἐκ- (ek-), from preposition ἐκ, ἐξ (ek, ex), "out," and of verb λείπω (leípō), "to leave". 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 syzygy is the alignment of three or more celestial bodies in the same gravitational system along a straight line. The word is usually used in context with the Sun, Earth, and the Moon or a planet, where the latter is in conjunction or opposition. Solar and lunar eclipses occur at times of syzygy, as do transits and occultation there is a syzygy between a star and two celestial bodies, such as a planet and a moon.

The shadow cast by the object closest to the star intersects the more distant body, lowering the amount of luminosity reaching the latter's surface. The region of shadow cast by the occulting body is divided into an umbra, where the radiation from the star's radiation-emitting photosphere is completely blocked, and a penumbra, where only a portion of the radiation is blocked.

Similar to 0 things you like: