Autumnal Equinox

Point at which on the celestial sphere that the equator and the Ecliptic intersect. Generally the autumnal equinox occurs on or about September 23 in the northern hemisphere; this also signifies spring in the southern hemisphere. [Encyclopedia of Astronomy; Satterthwaite, Gilbert; 29; 1971; St. Martins Press; NY.] [Glossary of Astronomy and Astrophysics; Hopkins, Jeanne; 51; 1976; University of Chicago; Chicago.] [Journal of Atmospheric and Solar-Terrestrial Physics; v66; 463-479; 2004.]