equi·​nox | \ˈē-kwə-ˌnäks, ˈe- \

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

Thursday, September 22, is the date of the autumn equinox, the first official date of fall. Avery Thompson, Popular Mechanics, "This Is the Exact Minute That Fall Will Begin," 21 Sep. 2016 Cassini found its most stunning ring surprises during the time surrounding the August 2009 equinox. Carolyn Porco, Scientific American, "Cassini at Saturn: A Retrospective," 1 Oct. 2017 Pömmelte henge, however, has its four entrances aligned with dates half way between the equinoxes and solstices. Fox News, "German ‘Stonehenge’ site reveals 10 dismembered bodies of women, children," 1 July 2018 Nowadays, thousands of people flock to Stonehenge each year to celebrate the solstices and equinoxes, many of them decked out in traditional pagan garb. Author: Justin Grieser, Anchorage Daily News, "Five things to know about the longest day of the year," 21 June 2018 The sundial shows the most exact time at the spring and autumn equinoxes. Karel Janicek, Fox News, "New role for Czech Republic TV tower: A giant sundial," 20 Apr. 2018 Technically speaking, the equinox occurs when the sun is directly in line with the equator. Brian Resnick, Vox, "Summer is for meteor showers and stargazing. Here’s how to watch.," 22 June 2018 To celebrate the spring and fall equinox, Hotel Chaco in Albuquerque, N.M., and the tour operator Heritage Inspirations are offering two-day trips to the Pueblo ruins at Chaco Canyon National Historic Park. Elaine Glusac, New York Times, "Glamping Slips Into the Mainstream," 15 June 2018 Nevertheless, what the region is witnessing Wednesday is a bona fide rarity, a post-equinox significant snowstorm, especially a daytime one. Anthony R. Wood, Philly.com, "Spring snow a rarity in Philly, but it has been worse, much worse," 21 Mar. 2018

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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Statistics for equinox

Last Updated

12 Nov 2018

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Time Traveler for equinox

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

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English Language Learners Definition of equinox

: a day when day and night are the same length


equi·​nox | \ˈē-kwə-ˌnäks, 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

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