Julian calendar is a calendar, named after Julius Caesar in 46 BC undertook a reform of the Roman calendar. The reform meant that the year was set to 365 days and the leap year with an extra day would occur every four years and that the phases of the moon would no longer have any bearing on the calendar. Suetonius wrote that the calendar had also been brought into disarray because the priest college had added days and months as they pleased, so that harvest and wine festivals no longer occurred at the right time of year. To correct chronology for this mess needed in 46 BC cover 445 days, and was therefore called annus confusionis.
In the years from 42 BC to 9 BC was due to a misunderstanding leap year every three years (years BC 42, 39, 36, 33, 30, 27, 24, 21, 18, 15, 12 and 9), i.e. leap year 12 in place of the 9th the Emperor Augustus ordered that the next twelve years from the year 8 BC was shot years absent. Last year miss leap day in accordance with the general rule thus became year 4 AD and year 8 the first correct the leap year. Thus, the Julian calendar worked as intended since the year 5 AD.
When the Julian calendar was introduced in 45 BC considered equinox occurs on 24 March. At the Council of Nicaea 325 had "moved" until 21 March. Although the exact astronomical timing deviates somewhat small, the three-day difference essentially correct. The explanation is that the difference between 0.0078 tropical year and calendar for 370 years accumulated to 2.886 days. The change in three days between the calendar's introduction and Nicaea meeting surprised its delegates (apparently without taking seriously the calendar's tendency to continuously remove themselves from the tropical year) "fixed" the vernal equinox in the future to 21 March. Interest in the Vernal Equinox date Nicaea meeting depended on the relationship with time for the Easter celebration. The timing of Easter Sunday confirmed the meeting with a very well known formula of "the first Sunday after the first full moon after the vernal equinox."
In Sweden used the Julian calendar until 1753 when it was replaced by the Gregorian calendar. (During a brief interlude, the years 1700 to 1712, was, however, the Swedish calendar.)
© Genney