What religion celebrates Easter Sunday on Sunday May 5 2013?

Answer 1

Eastern Orthodox Churches, including the Russian Orthodox and Greek Orthodox Churches for example, still use the Julian calendar to calculate the date of Easter.

The Julian calendar was replaced by the Gregorian calendar beginning in 1582 because March 21, which had been accepted to be the date of the vernal equinox, was drifting away from the actual vernal equinox under the Julian calendar at the rate of an extra day every 128 years.

It had been determined that Easter should never fall before the vernal equinox, so one of the rules governing the date of Easter is that it never falls earlier than the 22nd of March. The Eastern Orthodox Churches follow the rule that Easter never falls earlier than the 22nd of March of the Julian calendar, which is the 4th of April on the Gregorian calendar during most of this century. And since Easter is always the Sunday after a full moon (by calculation, not observation, contrary to popular belief), the Eastern Easter is often a month after the Western Easter.