autumnal equinox

Other forms: autumnal equinoxes

Definitions of autumnal equinox

1. noun

   the moment when the sun's rays shine directly on the equator, marking the beginning of autumn (fall) in either the northern or southern hemisphere
   synonyms: fall equinox

   type of:

   equinox

   either of two times of the year when the sun crosses the plane of the earth's equator and day and night are of equal length
2. noun

   (astronomy) the point in the sky, currently in the constellation of Virgo, where the sun's apparent path crosses the earth's equator from north to south
   type of:

   equinoctial point, equinox

   (astronomy) either of the two celestial points at which the celestial equator intersects the ecliptic