Gregorian calendar It also specifies its epact relative to 1 January, in contrast with the Julian calendar, which specified it relative to 22 March. The old date was derived from the Greek system: the earlier "Supputatio Romana" specified it relative to 1 January. During the period between 1582, when the first countries adopted the Gregorian calendar, and 1923, when the last European country adopted it, it was often necessary to indicate the date of some event in both the Julian calendar and in the Gregorian calendar, for example, "10/21 February 1750/51", where the dual year accounts for some countries already beginning their
Adoption of the Gregorian calendar to diverge from Gregorian. There will be no difference between the two calendars until 2800. The Greek Orthodox Church of Jerusalem, Russian Orthodox Church, Serbian Orthodox Church, Georgian Orthodox and Apostolic Church, Polish Orthodox Church, Macedonian Orthodox Church and the Greek Old Calendarists did not accept the Revised Julian calendar, and continue to celebrate Christmas on 25 December in the Julian calendar, which is 7 January in the Gregorian calendar until 2100. All of the other Eastern churches, the Oriental Orthodox churches (Coptic Orthodox Church of Alexandria, Ethiopian Orthodox Tewahedo Church, Eritrean Orthodox Tewahdo Church, and Syriac Orthodox Church) continue