The First Day of Spring

Usually, the spring equinox happens on March 20 or 21. The 2016 spring equinox happened during the very early hour of Sunday at 12:30 a.m. EDT, making it the earliest spring equinox since 1896.
Addendum:
It happens because of leap year and imperfection of Gregorian calendar system that can't quite account for Earth's annual revolution around the sun. By the time we reach the 2300s, however, we'll be back on track and most spring equinoxes will fall on March 21st. Our calendar system is based on a cycle of 400 years, more information why we have leap days and 400 year cycle at http://blogs.discovermagazine.com/badastronomy/2012/02/29/why-we-have-leap-days-2/#.Vu9FK-TmpPY