Eastern Orthodox and Western (Catholic and Protestant) Churches more often than not do not celebrate Easter on the same day.
On average, the dates coincide every 4 years, but this average is thrown off every now and then by longer intervals (7 years until 2025 when the conjunction recurs next, or 10 between 1991 and 2000). Sometimes, the alignment happens two years in a row, sometimes the gap is two years…
In other words, it’s not a neat pattern. So what’s going on?
I’ve talked about the calendar (Julian) used by the Orthodox Church.
This is a different date-calculation issue, although was also caused by the same Pope Gregory XIII in 1583 AD.
Back when Pope Gregory created the Gregorian calendar, he also decreed that some of the rules governing the date of Easter need not apply.
See, back in 325 AD at the Council of Nicea (today this ancient city is within the boundaries of the modern Turkish city of İznik), the dates of all major holidays were decided upon, including Easter. Unlike Christmas, which became a holiday with a set date, Easter’s date would have to be calculated, so it would always fall on a Sunday.
And not just any Sunday. It would have to be the first Sunday after the first full moon of Spring (that is after the Spring equinox). But it also has to be after the Jewish Passover, because the days leading to the Crucifixion and Resurrection include a Passover meal that Jesus shared with his Apostles.
The Orthodox Churches continue to follow this rule.
But Pope Gregory XIII decided that there was no need to pay attention to the date of Passover, and thus the dates of Catholic (and Protestant) Easter and those of Orthodox Easter separated.
A difference of dates doesn’t mean a difference of meaning. Easter (Paskha, the Feast of the Resurrection) is the same for all Christians. The many colors of the holiday come from the many outward traditions associated with it, the many cultural and ethnic traditions, the many languages, but all sing and praise the same event. Even if the local name of the holiday harks to an association to an ancient pagan cult, the modern Christian Feast is the same all around. This year, church bells will ring on the same date around the whole world.
But not on the same hour. Time zones: the sun wins the last time battle.