"Easter Day is always the
Sunday after the full moon that occurs on or after the spring equinox
on March 21, a date which is fixed in accordance with an ancient
ecclesiastical computation, and which does not always correspond to
the astronomical equinox. This full moon may happen on any date
between March 21 and April 18 inclusive. If the full moon falls on a
Sunday, Easter Day is the Sunday following. But Easter Day cannot be
earlier than March 22 or later than April 25."