High Quality Content by WIKIPEDIA articles! An equinox occurs twice a year (around 20 March and 22 September), when the tilt of the Earth`s axis is inclined neither away from nor towards the Sun, the center of the Sun being in the same plane as the Earth`s equator. The term equinox can also be used in a broader sense, meaning the date when such a passage happens. The name "equinox" is derived from the Latin aequus (equal) and nox (night), because around the equinox, night and day are about equal length.