autumnal equinox

[aw-tuhm-nl ee-kwuh-noks, ek-wuh-noks]

noun

1. equinox1

2. Also called autumnal point. the position of the sun at the time of the autumnal equinox.

autumnal equinox

noun

1. the time at which the sun crosses the plane of the equator away from the relevant hemisphere, making day and night of equal length. It occurs about Sept 23 in the N hemisphere (March 21 in the S hemisphere)

2. astronomy

   1. the point, lying in the constellation Virgo, at which the sun's ecliptic intersects the celestial equator

   2. the time at which this occurs as the sun travels north to south (23 September)

autumnal equinox

1. See under equinox

Word History and Origins

Origin of autumnal equinox¹

First recorded in 1670–80

Example Sentences

Or, as we say north of the equator, happy autumnal equinox!

Read more on Scientific American

On September 23, 2023, the autumnal equinox will signal the coming of fall for the Northern Hemisphere.

Read more on National Geographic

Traditionally, summer and winter solstices helped mark the changing of the seasons—along with their counterparts, the spring and autumnal equinoxes.

Read more on National Geographic

In an email, Dr. Nixon said his team was particularly excited to see what would happen in 2025, when Titan would reach its northern autumnal equinox.

Read more on New York Times

This year, the warm days have not only surpassed the September 22 autumnal equinox but are expected to continue through Oct.

Read more on Seattle Times