Did you know that the first day of Spring is on the 20th or 21st depending on the day the vernal equinox lands on. This chart shows the date and time of the equinox:
It comes from the site: http://scienceworld.wolfram.com/astronomy/VernalEquinox.html
Now, if I can only figure out how they decide when Easter will be......
Hehe...I found the "Easter" thing, too: http://www.straightdope.com/classics/a1_126a.html
Easter falls on the first Sunday subsequent to the first full moon after the vernal equinox (March 21). Thus, it can occur as early as March 22 and as late as April 25. (If the full moon after the equinox falls on Sunday, Easter follows a week later.)
the next one will be 2007 .... it's a 12 year increment. Last one was 1995.
Of course, 2007 is year 4704 on the Chinese calendar