Now, is the vernal equinox March 21 in Australia, or is that called the autumnal equinox? Easter is the first Sunday after the first FULL moon after the vernal (Spring) equinox. Passover, of course, is on the 14th of Nisan [of course :)]. Since the Jewish calendar is a lunar calendar and Easter is based on a lunar event, there is a relationship. Somewhere along the history of the evolution of the Christian calendar, the date of Easter came to be based directly on lunar events and not on the date of Passover.
-Joe Offer-