A congregant asked me a question before Easter about why the date of Easter moves every year, while Christmas is fixed. She mentioned she’d heard it had something to do with lunar movements. I didn’t know the answer, I thought it was something about a fixed number of days after Christmas being Epiphany, and then further Christian days following from there. So, we asked my friend Claude — an AI model — and I really liked the response. Here it is in full:
Christmas celebrates a fixed historical date (or rather, a date the church fixed — 25 December). The Gregorian calendar is solar, so 25 December always lands in the same place each year.
Easter follows a rule set in 325 A.D. at the Council of Nicaea: the first Sunday after the first full moon after the spring equinox. That rule deliberately mirrors the Jewish lunar calendar, because the crucifixion and resurrection happened during Passover, which is itself a lunar festival (14 Nisan). Since full moons cycle every 29.5 days and don’t align neatly with our 365-day solar year, Easter wanders between 22 March and 25 April.
There’s a Lutheran angle worth noting: the date of Easter matters less than the fact of it. Luther wasn’t particularly fussed about the calendar controversy — he cared that the resurrection was proclaimed. But the wandering date does mean Easter never becomes too domesticated or predictable, which suits the theology rather well. The resurrection broke into history unexpectedly; it still refuses to sit still on the calendar.
Ps Schalk Treurnicht
