noun \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


noun    (Concise Encyclopedia)

Either of two moments in the year when the Sun is exactly above the Equator and day and night are of equal length all over Earth; also, either of two points in the sky where the ecliptic and the celestial equator (see celestial sphere) intersect. The vernal equinox, when spring begins in the Northern Hemisphere, occurs about March 21, when the Sun moves north across the celestial equator. The autumnal equinox falls about September 23, as the Sun crosses the celestial equator going south. See also solstice.


Next Word in the Dictionary: equip (verb)
Previous Word in the Dictionary: equinoctial year
All Words Near: equinox

Seen & Heard

What made you want to look up equinox? Please tell us where you read or heard it (including the quote, if possible).