Revised Julian calendar
The Revised Julian calendar is a calendar that was considered for adoption by the Eastern Orthodox Church at a convention in Istanbul in 1923. It was made by Milutin Milankovic. The civil part of the calendar is identical to the Gregorian calendar except for the leap year rule, which is that leap years are divisible by 4, except for years divisible by 100 that do not leave a remainder of 200 or 600 when divided by 900. This means that the two calendars will first differ in 2800, a leap year in the Gregorian calendar, but a common year in the Revised Julian calendar.
This leap year rule gives an average year length of 365.242222… days, which is very close to the current length of the mean tropical year. However, the vernal equinox tropical year is slightly longer, so for a few thousand years the Revised Julian calendar doesn't do as good a job as the Gregorian calendar at keeping the vernal equinox on or close to March 21, after which the tropical year in days would have changed in a way not predictable at present.
The Revised Julian calendar was adopted in 1923 by the Greek and Syrian Orthodox churches, among others (the New calendarists), while the Russian and Serbian Orthodox churches, among others, remained on the Julian calendar (the Old calendarists). However, all Eastern Orthodox churches continue to use the Julian calendar for computing the date of Easter.
