equinox

noun

equi·​nox ˈē-kwə-ˌnäks  ˈe- 

1

: either of the two points on the celestial sphere where the celestial equator intersects the ecliptic

2

: either of the two times each year (as about March 21 and September 23) when the sun crosses the equator and day and night are everywhere on earth of approximately equal length

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Equinox and the Seasons

Equinox descends from aequus, the Latin word for "equal" or "even," and nox, the Latin word for "night"—a fitting history for a word that describes days of the year when the daytime and nighttime are equal in length. In the northern hemisphere, the vernal equinox marks the first day of spring and occurs when the sun moves north across the equator. (Vernal comes from the Latin word ver, meaning "spring.") The autumnal equinox marks the first day of autumn in the northern hemisphere and occurs when the sun crosses the equator going south. In contrast, a solstice is either of the two moments in the year when the sun's apparent path is farthest north or south from the equator.

Examples of equinox in a Sentence

Recent Examples on the Web

The meteorological end to the season is Friday, February 28, 2025 while the astronomical end is on Thursday, March 20, 2025, at the start of the spring equinox, according to the Old Farmer’s Almanac. —Cailey Gleeson, Journal Sentinel, 21 Nov. 2024

Winter extends from the winter solstice – the shortest day of the year – to the vernal equinox, the start of spring. —Clare Mulroy, USA TODAY, 10 Nov. 2024

The Harvest Moon, the traditional name given to the full moon closest to the autumnal equinox, which provides extra light for fall harvests. —Tiffany Acosta, The Arizona Republic, 17 Sep. 2024

This year the first day of fall, also called the autumnal equinox, is Sunday, Sept. 22. —Alexis Simmerman, Austin American-Statesman, 16 Sep. 2024

Word History

Etymology

Middle English, from Anglo-French or Medieval Latin; Anglo-French equinocce, from Medieval Latin equinoxium, alteration of Latin aequinoctium, from aequi- equi- + noct-, nox night — more at night

First Known Use

14th century, in the meaning defined at sense 1

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Kids Definition

equinox

noun

equi·​nox ˈē-kwə-ˌnäks  ˈek-wə- 

: either of the two times each year about March 21 and September 23 when the sun appears overhead at the equator and day and night are everywhere of equal length

Etymology

Latin equinoxium (same meaning), derived from earlier Latin aequi- "equal" and noct-, nox "night" — related to nocturnal