Autumnal Equinox Definition

noun
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.
American Heritage
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.
American Heritage

The moment when the sun appears to cross the celestial equator, heading southward.

Wiktionary

The point where the ecliptic intersects the celestial equator at that time.

Wiktionary
Synonyms:
Antonyms:

Other Word Forms of Autumnal Equinox

Noun

Singular:
autumnal equinox
Plural:
autumnal-equinoxes

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