Autumnal Equinox Definition
One of two points at which the ecliptic intersects the celestial equator. At the autumnal equinox, the sun is moving along the ecliptic in a southeasterly direction.
The moment at which the sun passes through this point on or about September 23, marking the beginning of autumn in the Northern Hemisphere and spring in the Southern Hemisphere.
The moment when the sun appears to cross the celestial equator, heading southward.
The point where the ecliptic intersects the celestial equator at that time.
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