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noun equi·nox \ˈē-kwə-ˌnäks, ˈe-\

: a day when day and night are the same length

Full Definition of EQUINOX

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

Origin 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

Other Astronomy Terms

gibbous, nadir, nebulous, penumbra, retrograde, sidereal, syzygy, wane, wax, zenith
EQUINOX Defined for Kids


noun equi·nox \ˈē-kwə-ˌnäks, ˈe-kwə-\

Definition of EQUINOX for Kids

:  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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