Equinox - In astronomy, an equinox is defined as the moment when the sun reaches one of two intersections between the ecliptic and the celestial equator.

The last two days of the year, in spring and autumn, when the hours of daylight and of night are equal.

This is the time when the Sun crosses the celestial equator. There are two equinoxes; Vernal (Spring), around March 21st and Autumnal (Autumn) around September 23rd. On these dates, day and night are equal. Actual dates and times vary due to the Earth's precession.

The culminating point of spring or autumn. At the spring equinox, the earth's north pole is midway between the winter and summer solstices and entering into the warming trend of summer. At the autumnal equinox, the earth's noth pole is midway between the winter and summer solstices and entering into the cooling period of winter.