A day in March that is the beginning of spring and a day in September that is the beginning of fall, are examples of the equinox.
- the time when the sun in its apparent annual movement along the ecliptic crosses the celestial equator, making night and day of equal length in all parts of the earth: in the Northern Hemisphere the vernal equinox occurs about March 21 and marks the beginning of spring, and the autumnal equinox occurs about September 22 and marks the beginning of autumn
- either of the two points on the celestial sphere where the sun's path crosses the celestial equatoralso called equinoctial point
Origin of equinoxMiddle English from Old French equinoxe from Medieval Latin aequinoxium from Classical Latin aequinoctium from aequus (see equal) + nox, night
- Either of two points on the celestial sphere at which the ecliptic intersects the celestial equator.
- Either of the two times during a year when the sun crosses the celestial equator and when the length of day and night are approximately equal; the vernal equinox or the autumnal equinox.
Origin of equinoxMiddle English from Old French equinoxe from Medieval Latin aequinoxium from Latin aequinoctium aequi- equi- nox noct- night ; see nekw-t- in Indo-European roots.
celestial sphere showing the positions of the autumnal and vernal equinoxes
(plural equinoxes or equinoctes)