Christmas, celebrating the birth of Jesus, is observed Dec. 25 by most of Christendom. But because different calendars are used to determine when the holiday is, most Armenian churches celebrate the holiday Jan. 6 and certain Eastern Orthodox churches--Serbian and traditional Russian--observe the day Jan. 7.
TRADITION: The earliest evidence of the observance of Christmas is from 4th-Century sources. In Rome, sometime before AD 336 the church celebrated the birthday Dec. 25. In the Eastern churches, Jesus' birth and his baptism were celebrated together on Epiphany in early January. But before the end of the century most Eastern churches moved the observance to Dec. 25. Historians note that the Christian holiday thus competed with holidays in the Roman world--the Saturnalia (Dec. 17), one of merrymaking and gift exchanges; the birth date of Mithra (Dec. 25), an Iranian mystery god with a popular following, and the Roman New Year (Jan. 1), when houses were decorated with greenery and lights.
OBSERVANCES: Although the gift-bearing Santa Claus and other secular lore mixes freely in popular celebrations, churches focus on the Nativity accounts found in the New Testament Gospels of Matthew and Luke. Manger scenes depict a humble birth and often combine distinctive elements from the two stories--shepherds from Luke and the Magi, or "wise men," and the Bethlehem star from Matthew.
Roman Catholic parishes usually celebrate a Christmas Mass at midnight on Christmas Eve. Not all churches schedule services on Christmas Day; fewer may do so this year because the holiday falls one day after the Sunday day of worship.