The Julian calendar date Thursday October 4, 1582 was followed by the Gregorian calendar date Friday October 15, 1582. Consequently, their Easter Sunday dates are identical up to 1582, then from 1583 onwards often differ from those of Western churches.In some years the Orthodox Easter Sunday occurs on the same day as the Western Easter Sunday.For example, this occurred in 1990 because the Western Easter Sunday date of (Gregorian calendar) April 15, 1990 is the same as the Orthodox Easter Sunday date of (Julian calendar) April 2, 1990.In most years, Orthodox Easter follows Western Easter by one or more weeks.
April 3 in 1922) is their Orthodox Easter Sunday date for that year.
Orthodox churches became fully autonomous in 1054 A.
D., and celebrate their Easter always on the basis of the Julian calendar and the "19 PFM dates" table.
For example, year 1995 gave us a PFM date of April 5, and step 2 gave us a total result of 9.
Looking at Table E, this 9 shows that this PFM date occurs on a Tuesday, so we need to add 5 days to find the next Sunday, which is April 10.
Easter Day was celebrated either: (a) on or just after the first day of the Jewish Passover (no matter on which day of the week that Easter Day occurred), or (b) on a Sunday close to or on the first Passover Day. Precise information on this subject can be found on pages 415 to 425 of the Explanatory Supplement to the 1961 Astronomical Ephemeris.