Thanks to a decision made more than 400 years ago, not all Christians observe the holiday on December 25.
“Christmas is over, so why are 12 percent of the world’s Christians waiting until January 7 to celebrate? Orthodox Christmas is celebrated by approximately 260 million people worldwide, both in majority-Orthodox countries in Eastern Europe, like Russia and Greece, and in communities in Ethiopia, Egypt, and elsewhere.
Marked by devout vigils and traditional feasts, the holiday traces its origins back to the centuries-old decision of Orthodox churches to split from the Catholic church and adhere to a calendar that differs from the one used by most of the world today. Here’s what you need to know.
Christianity adopts a standardized calendar
Disagreements as to when to officially recognize the birth of Jesus Christ stretch back all the way to A.D. 325, when a group of Christian bishops convened the religion’s first ecumenical conference—a gathering to rule on issues of religious doctrine.
One of the First Council of Nicaea’s most important agenda items was to standardize the date of the church’s most important holiday, Easter. To do so, they decided to base it on the Julian calendar, a solar calendar which Roman ruler Julius Caesar had adopted in 46 B.C. on the advice of Egyptian astronomer Sosigenes in an attempt to clean up Rome’s own messy lunar calendar.
But Sosigenes’ calculations had an issue of their own: They overestimated the length of the solar year by about 11 minutes. As a result, the calendar and the solar year became increasingly out of sync as the centuries progressed.
Christianity’s great calendar schism
By 1582, the dates of important Christian holidays had drifted so much that Pope Gregory XIII was concerned. He convened another group of astronomers and proposed a new calendar, known as the Gregorian calendar.
The new calendar solved a number of tricky issues that had accumulated over the years, and the majority of the Christian world adopted it.
But the Orthodox Church disagreed. During the Great Schism of 1054, it had split into its own arm of Christianity after centuries of mounting political and doctrinal difference. Orthodox Christians do not recognize the Pope as the leader of the church, reject the concept of purgatory, and disagree over the origin of the Holy Spirit, among other differences.
Following Pope Gregory’s course correction would have meant accepting an occasional overlap between Passover and Easter—a move that went against holy texts of Orthodox Christianity. So the Orthodox Church rejected the Gregorian calendar and continued to rely on the Julian calendar.
It stayed that way for centuries, and the calendar drift continued. By 1923, there was a 13-day difference between the two calendars, putting Orthodox Christmas 13 days after December 25.Why some people celebrate Christmas in January — We All Deserve Better