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 intersections between the rings and the water channel mark the building shadow at specific hours during the equinoxes, and one outer ring features a series of fountains that celebrate the 24 solar terms of the traditional Chinese calendar. —Adam Williams, New Atlas, 4 Nov. 2024

The Hunter's Moon is the full moon immediately following the autumnal equinox and the use of this specific term dates back to about 1710, per NASA. —Mia Taylor, Parents, 16 Oct. 2024

September’s equinox, the moment when day and night briefly achieve perfect balance, serves as a metaphor for equilibrium. —Olivier Blum, Forbes, 15 Oct. 2024

The harvest moon is the full moon that occurs near the autumn equinox (which is on 22nd September) and so this eclipse will be known as a time of cultivating, growing and releasing. —Lisa Stardust, refinery29.com, 17 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