first day of spring 2011

Sunday, March 20, 2011 marks the vernal equinox, and what many people in the Northern Hemisphere -- particularly the U.S. -- refer to as the first day of spring.
At 7:21 p.m. EST astronomical spring begins in the Northern Hemisphere as defined by International Astronomical Union, though it marks the beginning of fall for those in the Southern Hemisphere. On the vernal equinox, day and night are nearly identical in length -- 12 hours each -- at the equatorial plane