equinox—The two points in the celestial sphere where the celestial equator intersects the ecliptic; also the times when the sun crosses the equator at these points. See also equinox, autumnal; equinox, vernal.

equinox, autumnal—That point of intersection of the ecliptic and the cele^,11,11 equator occupied by the sun as it changes from north to south declination, about September 23; first point of Libra, September equinox. See also equinox.

equinox, vernal-¹That point of intersection of the ecliptic and the celestial equator, occupied by the sun as it changes from south to north declination, on or about March 21; first point of Aries, March equinox. ² That instant the sun reaches the point of zero declination when crossing the celestial equator, from south to north. See also equinox.

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Source: NSPS “Definitions of Surveying and Related Terms“, used with permission.

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