how do they decide when easter is
Easter is set using a formula that ties it to the spring equinox and a special “church full moon,” so it moves around the calendar instead of staying on a fixed date. In short: for most Western churches, Easter is the first Sunday after the Paschal full moon on or after March 21.
Core rule in one line
- Western Easter (Catholic, most Protestants) = first Sunday after the Paschal full moon that falls on or after March 21, which the church treats as the date of the spring equinox.
What “Paschal full moon” means
- The Paschal full moon is not the actual astronomical full moon but a calculated one based on tables and a 19‑year lunar cycle (the Metonic cycle).
- These church tables were created so people did not have to watch the sky every year but could look up the date instead.
Why the date changes every year
- Because the full moon date shifts each year, Easter can fall anywhere from March 22 to April 25 in the Western (Gregorian) calendar.
- The rule links a solar event (spring equinox, fixed as March 21) with a lunar event (Paschal full moon), so the holiday “moves” instead of staying put like Christmas.
Brief history behind the rule
- In 325 CE, the Council of Nicaea decided Christians should celebrate Easter on the same day and set the basic rule: first Sunday after the first full moon on or after the vernal equinox.
- The Western church later locked the equinox to March 21 and refined the calendar with the Gregorian reform in 1582 to keep the date aligned with the seasons.
What about Orthodox Easter?
- Many Eastern Orthodox churches still use the older Julian calendar and also tie Easter to Passover, so their Easter often falls on a different, usually later, Sunday (roughly early April to early May in Gregorian dates).
- The underlying idea is similar—Sunday after a Paschal full moon near the spring equinox—but the calendar system and some details differ, which shifts the date.
Information gathered from public forums or data available on the internet and portrayed here.