Calendar & Easter History

Calendar & Easter History
I was wondering how easter dates are calculated, when my friend and collegue from Romania told me he is having it on May first and that He is a Chirstian Orthodox. I was confused. I have many orthodox friends in India, they never said they have easter on another day.
When I investigated and found that easter is calcuted in 3 ways and these three ways used in diffrent parts of the world.

METHOD 1 - The original calculation based on the Julian calendar

METHOD 2 - The original calculation, with the Julian date converted to the equivalent Gregorian date

METHOD 3 - The revised calculation based on the Gregorian calendar

And the link provides algorithms for calculations for these Easter dates.


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WESTERN ORTHODOX
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23 April 2000 30 April 2000
15 April 2001 15 April 2001
31 March 2002 5 May 2002
20 April 2003 27 April 2003
11 April 2004 11 April 2004
27 March 2005 1 May 2005
16 April 2006 23 April 2006
8 April 2007 8 April 2007
23 March 2008 27 April 2008
12 April 2009 19 April 2009



Definition of Easter Sunday Date
Easter Sunday is the Sunday following the Paschal Full Moon (PFM) date for the year. In June 325 A.D. astronomers approximated astronomical full moon dates for the Christian church, calling them Ecclesiastical Full Moon (EFM) dates. From 326 A.D. the PFM date has always been the EFM date after March 20 (which was the equinox date in 325 A.D.).

Easter Sunday date is the Sunday after the Paschal Full Moon (PFM) date
The PFM is the first Ecclesiastical Full Moon (EFM) date after March 20
PFMs are pre-defined (see above)
EFMs are approximated astronomical full moon dates, not actual astronomical full moon dates