Every year, I receive questions from readers confused by the fact that the Eastern Orthodox celebrate Easter on a different day (in most years) from Catholics and Protestants. Now, a reader notes a similar situation regarding the date of Christmas:
A friend of mine—a convert to Eastern Orthodoxy—tells me that the real date of Christ's birth is not December 25 but January 7. Is this true? If so, why do we celebrate Christmas on December 25?
There's a bit of confusion here, either in the mind of the reader's friend or in the way that the reader's friend explained this to the reader. The fact is, all Eastern Orthodox celebrate Christmas on December 25; it just seems like some of them celebrate it on January 7.
No, that isn't a trick answer—well, not much of a trick, at least. If you've read any of my discussions of the reasons for the different dates of Easter in East and West, you'll know that one of the factors that comes into play is the difference between the Julian calendar (used in Europe up until 1582, and in England until 1752) and its replacement, the Gregorian calendar, which is still in use today as the standard global calendar.
Pope Gregory XIII introduced the Gregorian calendar to correct astronomical inaccuracies in the Julian calendar, which had caused the Julian calendar to get out of sync with the solar year. In 1582, the Julian calendar was off by 10 days; by 1752, when England adopted the Gregorian calendar, the Julian calendar was off by 11 days.
Until the turn of the 20th century, the Julian calendar was off by 12 days; currently, it is 13 days behind the Gregorian calendar, and will remain so until 2100, when the gap will grow to 14 days.
The Eastern Orthodox still use the Julian calendar to calculate the date of Easter, and some (though not all) use it to mark the date of Christmas. That's why I wrote that all Eastern Orthodox celebrate Christmas (or, rather, the feast of the Nativity of Our Lord and Savior Jesus Christ, as as it is known in the East) on December 25. Some join Catholics and Protestants in celebrating Christmas on December 25 on the Gregorian calendar, while the rest celebrate Christmas on December 25 on the Julian calendar.
Add 13 days to December 25 (to make the adjustment from the Julian calendar to the Gregorian one), and you arrive at January 7.
In other words, there is no dispute between Catholics and Orthodox over the date of Christ's birth. The difference is entirely the result of the use of different calendars.
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