Syzygy (astronomy)

In astronomy, a syzygy (/ˈsɪzᵻdʒi/; from the Ancient Greek σύζυγος suzugos meaning, "yoked together") is a straight-line configuration of three celestial bodies in a gravitational system.

The word is often used in reference to the Sun, Earth, and either 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 occultations. The term is often applied when the Sun and Moon are in conjunction (new moon) or opposition (full moon).

The word syzygy is often loosely used to describe interesting configurations of planets in general. For example, one such case occurred on March 21, 1894 around 23:00 GMT, when Mercury transited the Sun (as could have been seen from Venus), and Mercury and Venus both simultaneously transited the Sun as seen from Saturn. It is also used to describe situations when all the planets are on the same side of the Sun although they are not necessarily in a straight line, such as on March 10, 1982.

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