Equinox

 Sept. 22: Happy Equinox! At 9:15 a.m. EDT (1315 GMT), autumn arrives in the Northern Hemisphere while the Southern Hemisphere will have its first day of spring. It happens two times a year, Vernal & Autumnal, spring and fall.

"Equinox" literally means "equal night", giving the impression that the night and day on the equinox are exactly the same length; 12 hours each - about equal almost everywhere on Earth.

Incidentally, the biggest difference between the equinox and the solstice is that a solstice is the point during the Earth's orbit around the sun at which the sun is at its greatest distance from the equator, while during an equinox, it is at the closest distance from the equator.