The Julian Calendar for the Fixed Feasts

The Julian calendar, introduced under Julius Caesar in 46 BC and refined only slightly under Augustus a generation later, fixes the length of the year at three hundred sixty five and a quarter days, adding one leap day every four years with no exception ever made to that rule. The true solar year is a little shorter than that, by about eleven minutes, and the shortfall compounds year after year with nothing to correct it: by the time Pope Gregory XIII reformed the calendar in 1582, the drift had reached ten days, which the Gregorian reform corrected by dropping ten days from the calendar at a single stroke and by removing three leap years every four centuries afterward to keep the two calendars from drifting apart again in the future. A church that never adopted the Gregorian correction keeps accumulating the old, uncorrected drift at the same steady rate, which is why the Julian calendar now runs thirteen days behind civil reckoning rather than the ten days it was behind in 1582, and why a fixed feast kept on the unrevised calendar lands thirteen days later by the civil date than the identical feast kept on the Gregorian reckoning, a gap that will widen by a further day in the year 2100. Russia itself did not adopt the Gregorian calendar for civil purposes until 1918, well after most of Western Europe, which is part of why the October Revolution, which took place in late October by the old Russian civil reckoning, is now dated in November on the calendar in general use today.

Which Orthodox churches keep the unrevised calendar is not a fixed historical fact but a live and still moving line. In July 2023 the Orthodox Church of Ukraine's own local council voted to adopt the Revised Julian calendar for its fixed feasts, effective that September, a change reported at the time as part of a wider institutional distancing from Moscow rather than a purely calendrical decision, and corroborated by multiple independent outlets covering the vote. The Russian Orthodox Church, along with the Patriarchates of Jerusalem and Georgia, the Serbian Orthodox Church and the monastic communities of Mount Athos, took the opposite side of that same choice and remained on the unrevised calendar, so a decision first made in 1923 by a pan-Orthodox congress in Constantinople is still, a full century later, read as a marker of which jurisdiction a given church aligns itself with. Old Believers, who left the Russian church over a seventeenth century liturgical dispute unrelated to the calendar question, were never in any position to adopt either twentieth century reform in the first place and have kept the unrevised reckoning throughout, for reasons that predate the 1923 controversy by more than two hundred years and rest on an entirely separate historical grievance.