day 6 - xmas eve - The Coptic, Serbian (nice to meet you:)), Russian, Macedonian, and Georgian Orthodox Churches, as well as the Greek Orthodox Church of Jerusalem, use the Julian calendar, which is currently thirteen days behind the Gregorian calendar, so Christmas Eve for the adherents of those Churches coincides with January 6 of the following year in the Gregorian calendar.
Wikipedia surely can explain this much more better than me :) Merry Xmas Eve to all those who celebrate today!