The fact many Eastern Orthodox now celebrate Christmas on Dec. 25 adds to the confusion, especially since those who celebrate on Jan. 7 are still really celebrating on Dec. 25.
In the church's early years, a calendar established by Julius Caesar, known as the Julian calendar, was in use. But in 1582 by Pope Gregory XIII modified that calendar, which is calendar people use today.
So the Jan. 7 date on the Gregorian calendar is really the Dec. 25 date on the Julian. So for Christians following the "old" calendar," it appears they are celebrating Christmas on Jan. 7.
Rev. Andrew Harrison, (above, left, green sweater), pastor of St. John Kochurov in New Lenox, which is the south chapel of St. Luke The Evangelist Orthodox Church in Palos Hills, said the Orthodox continued using the "old" calendar until the 1920s when the Greek Orthodox Church adopted the "new" calendar to calculate its liturgical year.
Over time, most of the other Orthodox churches transitioned to the new calendar, too.
"In the OCA [Orthodox Church of America], most of the churches are on the new calendar," Harrison said. "But there are some who are still on the old calendar, including the Diocese of Alaska and the Serbian Orthodox Church."
(Members and guests at St. John Kochurov in New Lenox show off their ugly Christmas sweaters at the church. Those pictured include Tyler Holchik, the Rev. Andrew Harrison, Diane Wilzak, Roberta Spengler, Thomas Beckman, Ron Smith, Julia Wojcik and Katerina Wojcik).