syzygia

Syzygia is an astronomical term referring to a straight-line configuration of three or more celestial bodies in a gravitational system. Most commonly, it is used to describe the alignment of the Sun, Earth, and either the Moon or another planet.

The most well-known syzygies are full moons and new moons, which occur when the Moon aligns with the Sun and Earth. During a new moon, the Moon is between the Sun and Earth, and during a full moon, the Earth is between the Sun and the Moon. Eclipses, both solar and lunar, are specific types of syzygy. A solar eclipse happens when the Moon passes between the Sun and Earth, casting a shadow on Earth, and a lunar eclipse occurs when the Earth passes between the Sun and Moon, casting a shadow on the Moon.

The term syzygy also applies to the alignment of planets with the Sun and Earth. Such alignments can lead to phenomena like transits, where a smaller celestial body appears to move across the face of a larger one, such as a planet transiting the Sun. The gravitational forces exerted by celestial bodies during syzygy can have observable effects, such as influencing tides. The word syzygy originates from the Greek word syzygos, meaning "yoked together."