[skissane]

Added to that, in some (but not all) Orthodox majority countries, most notably Russia, Christmas is on 25 December by the old Julian calendar, which is on 7 January by the current Gregorian calendar (which everyone uses, Russia included, for civil/commercial/everyday use). It’s Gregorian date moves forward by one day every century (except for every fourth century, when it doesn’t.)

Some of the other Orthodox Churches (such as the Greeks) technically celebrate Christmas, not using the Gregorian calendar, but rather the “Revised Julian” - which happens to be identical to the Gregorian until 2800. I wonder if, come 2800, they’ll remember to move the date of Christmas, or if they’ll think “there’s no point to it, let’s not” (assuming of course that both they, and humanity as a whole, are still around in 2800)