when did the julian calendar come into effect
Julian calendar The Julian calendar, proposed by Julius Caesar in 46 BC (708 AUC), was a reform of the Roman calendar.[1] It took effect on 1 January 45 BC (AUC 709), by edict. It was the predominant calendar in the Roman world, most of Europe, and in European settlements in the Americas and elsewhere, until it was refined and gradually replaced by the Gregorian calendar, promulgated in 1582 by Pope Gregory XIII. The Julian calendar gains against the mean tropical year at the rate of one day in 128 years. For the Gregorian the figure is one day in 3,030 years.[2] The difference in the average length of the year between Julian (365.25 days) and Gregorian (365.2425 days) is 0.002%.
February 29 A leap day is observed because a complete revolution around the Sun takes approximately 6 hours longer than 365 days (8,760 hours). A leap day compensates for this lag, realigning the calendar with the Earth's position in the Solar System; otherwise, seasons would occur earlier than intended in the calendar year. The Julian calendar used in Christendom until the 16th century added a leap day every four years; but this rule adds too many days (roughly 3 every 400 years), making the equinoxes and solstices shift gradually to earlier dates. By the 16th century the vernal equinox had drifted to March 11, and the Gregorian calendar was introduced both to shift it back by omitting several days, and to reduce the number of leap years via the "century rule" to keep the equinoxes more or less fixed and the date of Easter consistently close to the vernal equinox.[1][2]