Christmas, Solemnity of the Nativity - the Christian tradition is a feast commemorating the birth of Jesus Christ. It is a liturgical feast of solid per December 25 (according to the Gregorian calendar). Christmas is preceded by a three-week waiting period (actually, four Sundays), known as Advent. In churches, which continue to celebrate the liturgy according to the Julian calendar (the Eastern Churches, mostly Greek Orthodox and the Orthodox Church), Christmas Day falls on December 25 of the Julian calendar, ie, out of 7 January Gregorian calendar.
