equi·​nox | \ ˈē-kwə-ˌnäks How to pronounce equinox (audio) , ˈe- How to pronounce equinox (audio) \

Definition of equinox

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," 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 This year, the autumn equinox is Wednesday, September 22, 2021. Sarah Zlotnick, Country Living, 16 June 2021 The equinox is the precise moment the sun's rays shine directly on the Earth's equator. Doyle Rice, USA TODAY, 19 Mar. 2021 Much like the phenomenon of balancing an egg upright during the equinox, which can be done equally well during any day of the year, metal objects can often stick to human skin. Ethan Siegel, Forbes, 23 June 2021 It’s defined as the full Moon that rises closest to the September equinox each year, and it’s the fourth full Moon—and the final notable astronomical sight—of summer 2021. Jamie Carter, Forbes, 19 June 2021 Astronomical spring begins this Saturday at 5:37 a.m. From that point forward, the sun will be highest in the sky at midday in the Northern Hemisphere, continuing that way until the autumnal equinox in September. Dave Epstein, BostonGlobe.com, 18 Mar. 2021 The equinox is widely expected to occur on schedule, providing at least psychic warmth. Washington Post, 21 Feb. 2021 This year, however, the Harvest Moon occurs in October, since the September full moon – known this year as the Corn Moon – occurred on Sept. 2, 20 days before the equinox. Leada Gore | Lgore@al.com, al, 1 Oct. 2020 Folks all over the planet actually did get nearly equal doses of day and night back during the spring equinox. CNN, 20 June 2021

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'equinox.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

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First Known Use of equinox

14th century, in the meaning defined at sense 1

History and Etymology for equinox

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

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Time Traveler for equinox

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The first known use of equinox was in the 14th century

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Dictionary Entries Near equinox

equinoctial year



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Last Updated

29 Jul 2021

Cite this Entry

“Equinox.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/equinox. Accessed 3 Aug. 2021.

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More Definitions for equinox



English Language Learners Definition of equinox

: a day when day and night are the same length


equi·​nox | \ ˈē-kwə-ˌnäks How to pronounce equinox (audio) , ˈe-kwə- \

Kids Definition of equinox

: either of the two times each year (as in spring around March 21 and in fall around September 23) when the sun's center crosses the equator and day and night are everywhere of equal length

More from Merriam-Webster on equinox

Nglish: Translation of equinox for Spanish Speakers

Britannica English: Translation of equinox for Arabic Speakers

Britannica.com: Encyclopedia article about equinox


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