equinox
  • noun either of the two occasions in the year, spring and autumn, when the sun crosses the celestial equator and night and day are each 12 hours long
  • Day on which the Sun is at the celestial equator, so that night and day are of 12 hours each. Due to northern hemisphere chauvinism they are called the spring or vernal equinox (around March 21) and the autumn equinox (around September 23).

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