Glossary term: Equinox

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Description: The equinox is the moment of the year in which the Sun, in its journey through the ecliptic, crosses the celestial equator. Th e word is derived from the Latin aequinoctium with aequus (equal) and nox (genitive noctis) (night). On the day of an equinox, daytime and nighttime are of approximately equal duration all over the planet, rather than just near to the equator. To an observer on Earth, the Sun rises exactly from the cardinal point east and moves, apparently, along the line of the celestial equator during that day, setting exactly in the west. There are two equinoxes per year, one around 20 March and one around 23 September. When the equinox is in March, it indicates the apparent passage of the Sun towards the northern hemisphere; in the September equinox the apparent passage of the Sun is to the south.

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