Easter, Easter Sunday (Orthodox)

Orthodox Easter is computed from the Julian calendar's own reckoning of the spring equinox and lunar cycle, the Julian computus this rule names directly, rather than from the Gregorian calendar the West adopted in 1582. The choice is deliberate continuity rather than an oversight, and it produces a date that can fall on the same day as Western Easter in some years and as much as five weeks later in others, since the Julian calendar's equinox now sits roughly thirteen days behind the Gregorian one and drifts further with each passing century.

A further principle shapes Orthodox practice beyond the calendar difference itself. Many Orthodox churches hold to an ancient rule, traceable to the early Church's own concern with the relationship between the Christian feast and the Jewish Passover it grew out of, that Easter should not be reckoned before Passover in a given year, a constraint the fixed Gregorian computus used in the West does not observe in the same way. The combination of the older calendar and this sequencing rule is why the Orthodox date, though it follows the same ancient formula Nicaea intended for the whole Church, has continued to diverge from Western practice for nearly five centuries rather than converging with it.