From the Latin aequus, equal, and nox, night, the great circle on the celestial sphere in the plane of the earth's equator, sometimes called the celestial equator. The sun is on the equinoctial on two occasions each year, these occurring on 21 March and 23 September, days known as the equinoxes. On these days the sun rises at 6 a.m. and sets at 6 p.m. (local time) at every place on earth. The two points of intersection of the equinoctial with the ecliptic are called the spring and autumnal equinoctial points respectively, or more usually the first points of Aries and Libra for the spring and autumnal equinoxes.
The word is also used as an adjective to describe phenomena happening at or about the time of the equinox, e.g. equinoctial gales, equinoctial rains.
Subjects: Maritime History.