Revised Julian calendar
The Revised Julian calendar, less formally the new calendar, also known as the Milanković calendar, is a calendar proposed in 1923 by the Serbian scientist Milutin Milanković as a more accurate alternative to both the Julian and Gregorian calendars. At the time, the Julian calendar was still in use by all Eastern Orthodox Church and affiliated nations, while Catholic and Protestant nations were using the Gregorian calendar, which had been proclaimed by Pope Gregory XIII's papal bull Inter gravissimas in 1582.