Easter is determined as the first Sunday after the Paschal Full Moon, which is the first full moon occurring on or after the spring equinox (fixed by the Church as March 21)
. This method was established by the Council of Nicaea in 325 CE to standardize the celebration of Easter across Christianity. Key points in determining Easter:
- The spring equinox is fixed by the Church as March 21, regardless of the actual astronomical equinox date, which can vary by a day or two depending on time zone
- The Paschal Full Moon is a calculated, ecclesiastical full moon date based on a 19-year Metonic cycle, not necessarily the exact astronomical full moon
- Easter falls on the Sunday following this Paschal Full Moon. If the full moon falls on a Sunday, Easter is celebrated the next Sunday
- Because of calendar differences, Western churches (using the Gregorian calendar) and Eastern Orthodox churches (using the Julian calendar) often celebrate Easter on different dates
In summary, Easter is a movable feast set by a lunar-solar calculation: the first Sunday after the first full moon on or after March 21
