Astronomically derived Easter is the Sunday after the full moon after the vernal equinox, and that's quite easy to calculate. I thought of implementing Computus, but gave up as it's so arbitrary that nothing worthwhile would be learned by implementing it. I implemented astronomical Easter instead, knowing that it's occasionally wrong: http://web.onetel.com/~hibou/fmj/tutorials/GregorianCalendar... - scroll down to Bell, Book, and Candle.