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The term Old Calendarist (cal-en-DAR-ist) refers to any Orthodox Christian or any Orthodox Church body which uses the historic Julian calendar (called "Old Style Calendar" or "Church calendar" or "Old Calendar"), and whose Church body is not in communion with the Orthodox Churches that use the New Calendar. The "Old Calendarists" (who are also sometimes styled "Old Calendar") are to be distinguished from Orthodox Christians or Orthodox Church bodies which are on the Old Calendar. The latter use the historic Julian calendar cited above, but are in communion with the Orthodox Churches that use the New Calendar (the Revised Julian calendar). Thus, to be "Old Calendarist" or "Old Calendar" is not the same thing as being "on the Old Calendar"; and the Russian Orthodox Church, for instance, is not Old Calendarist (or Old Calendar), but it is on the Old Calendar. There are a great many Orthodox Christians who are (or who belong to Churches that are) on the Old Calendar, but far fewer in number are the Orthodox Christians who are Old Calendar or Old Calendarist.
The Julian Calendar is commonly opposed to the Gregorian Calendar introduced to Christianity by the Pope during the 16th century. A revised form of the Julian Calendar, developed by the Serbian astronomer Milutin Milanković, which mostly coincides with the Gregorian one, was finally adopted by the Greek Orthodox Patriarchate of Constantinople in 1924 as well as by the autocephalous Church of Greece. A minority of Orthodox Christians regarded this as a surrender of the Orthodox Church to the West and to the Pope and continued following the old calendar; some of these also broke communion with those who had adopted the new calendar, thus creating their own church, or denomination, which means in the Latin "to take a new name".
This schism is the beginning of the Old Calendar Churches which suspended full communion and/or concelebration with other Orthodox churches ("New Calendarists") over the adoption by the latter of the Revised Julian calendar (called "New Calendar," although some churches did not specify the details of which New calendar they were adopting). This is the most common use of the term.
Those Orthodox Churches which remain in full communion with the New Calendarists and yet continue to use the Julian calendar, include the Orthodox Church of Jerusalem, the Russian Orthodox Church, the Serbian Orthodox Church, and the Georgian Orthodox Church. (The Julian calendar is also used by the Russian Orthodox Church Outside of Russia which has reunited with the Russian Orthodox Church.) Mount Athos subordinate to the Patriarchate of Constantinople also follows the Julian Calendar.
Some Orthodox Church bodies which are Old Calendarist have, in recent memory, sanctioned the practice of the New Calendar among some of their dioceses or parishes. For example, a group of parishes today known as the Bulgarian Diocese of the Orthodox Church in America were until 1976 a part of Russian Orthodox Church Outside of Russia (ROCOR). These parishes were permitted to practice the New Calendar even though the rest of ROCOR was on the Old Calendar. Thus, ROCOR at that time could have been called "New Calendarist."
- OrthodoxWiki article about the Old Calendarists
- The Ecclesiological Position of the Old Calendar Orthodox Church of Bulgaria, by Bishop Photii of Triaditsa