The time or date (twice each year) at which the sun crosses the celestial equator, when day and night are of equal length (about September 22 and March 20)
date at which day and night are of equal length
Another term for vernal equinox.
The equinox in spring, on about March 20 in the northern hemisphere and September 22 in the southern hemisphere
The equinox in autumn, on about September 22 in the northern hemisphere and March 20 in the southern hemisphere