An equinox refers to the two times a year when the equator is closest to the sun rather than the northern or southern hemisphere. This happens because the Earth spins at an angle. If the Earth wasn't tilted at a 23.5° angle everyday would technically be an equinox. The equinoxes mark the beginning of spring and fall.
In Latin, the word equinox means "equal night." This is appropriate since the equinoxes are considered the two days a year when day and night length are equal, both 12 hours. The spring equinox always occurs in March and the autumnal or fall equinox always takes place in September.
The vernal or spring equinox is coming up next week. This year's spring equinox will take place Monday March 20th at 6:28A.M. Days will get continuously longer as we move through spring into summer.