The spring equinox occurs at 1:14 a.m. EDT on Tuesday, March 20.
The equinox marks the end of winter and the official start of spring. Its the day when there are equal parts of day and night.
The days now will grow longer, until we reach the summer solstice the longest day of the year. The summer solstice is Wednesday, June 20, 2012.
The winter solstice has a special significance this year because of the Mayan calendar. That calendar finishes one of its great cycles on Dec. 21, 2012, leading to speculation and at least one movie that the world will end on that date.