The DateTime::Event::Easter module returns Easter events for DateTime objects.
From a given datetime, it can tell you the previous, the following and the
closest Easter event. The 'is' method will tell you if the given DateTime is an
Easter Event.

Easter Events can be Palm Sunday, Maundy Thursday, Good Friday, Black Saturday
and Easter Sunday. If that's not enough, the module will also accept an offset
so you can get the date for Pentecost (49 days after Easter Sunday) by passing
49. 

WWW: http://datetime.perl.org/