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
Did You Know?
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.
Origin and Etymology of 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
First Known Use: 14th century
EQUINOX Defined for English Language Learners
Definition of equinox for English Language Learners
: a day when day and night are the same length
EQUINOX Defined for Kids
Definition of equinox for Students
: 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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