For a quick calculation, between 1901 and 2099 the much more common Gregorian date equals the Julian date plus 13 days. rk note: 'til 2099? Who decided that? SEE ALL THE YELLOW HIGHLIGHTS HERE: JULIAN CALENDAR
Britain and the British Empire (including the eastern part of what is now the United States) adopted the Gregorian calendar in 1752. Sweden followed in 1753.
WHAT'S THIS? Terminalia?
Although the approximation of 365+1⁄4 days for the tropical year had been known for a long time,[10] ancient solar calendars had used less precise periods, resulting in gradual misalignment of the calendar with the seasons. rk note: there's more than one solar calendar?
The Orthodox Churches of Jerusalem, Russia, Serbia, Montenegro, Poland (from 15 June 2014), North Macedonia, Georgia, and the Greek Old Calendarists and other groups continue to use the Julian calendar, thus they celebrate the Nativity on 25 December Julian (which is 7 January Gregorian until 2100). rk note: Then what happens?
The Orthodox Church of Ukraine announced in late May 2023 that they would use the Gregorian calendar to celebrate Christmas on December 25, 2023, partly in reflection to Russia's invasion of the country in early 2022; the church continues to celebrate Easter on the date according to the Julian tradition.[95] rk note: Was that some kind of negotiating tool? I thought there was a war going on over there.
Most branches of the Eastern Orthodox Church use the Julian calendar for calculating the date of Easter, upon which the timing of all the other moveable feasts depends. Some such churches have adopted the Revised Julian calendar for the observance of fixed feasts, while such Orthodox churches retain the Julian calendar for all purposes.[96] rk note: What is a fixed feast? Does it have anything to do with spirit cooking?
The Ancient Assyrian Church of the East, an East Syriac rite that is commonly miscategorised under "eastern Orthodox", uses the Julian calendar, where its participants celebrate Christmas on 7 January Gregorian (which is 25 December Julian). The Assyrian Church of the East, the church it split from in 1968 (the replacement of traditional Julian calendar with Gregorian calendar being among the reasons), uses the Gregorian calendar ever since the year of the schism.[97] rk note: What was the schism about?