Equinox is the phenomena in astronomy when the Earth's axis is perpendicular to the plane in which the Earth moves around the sun, and in the broader sense, dates and events that mark the beginning of spring (around 21 March) and autumn (around 23 September). Points on the celestial sphere where the ecliptic intersects the celestial equator is called the equinox point. The sun in its apparent motion along the ecliptic passes through the vernal point at the moment of the vernal equinox and the autumnal point in time of autumn equinox.
To date of equinox directions of sunrise and sunset are closest to the exact directions of east and west, and in the time of equinox sun's rays illuminate the earth's equator at a right angle. Duration of day and night is approximately 12 hours, but due to the effects of the atmosphere is not exactly the same. Since 2008th to 2101th, the vernal equinox falls on 19th or 20th March.
Equinox is one of two moments during the year when the sun is directly over Earth's equator. In the spring in the Northern Hemisphere, the vernal equinox occurs around March 21st, in the fall equinox occurs around September 21st (though the exact date varies slightly from year to year). During equinox, the length of day and night are equal all over the world. In Europe, spring and autumn officially begin at the vernal and autumnal equinoxes.
Name equinox comes from Latin and contains two words: aequus (equal) and nox (night) - because then, night and day are equally long.