Julian vs Gregorian Calendar
Julian calendar The Julian calendar was introduced in 45BC by Julius Caesar, taking over from the Roman calendar . Under the Julian calendar each year has 365 days, except for a leap year every four years which has 366 days. This averages to 365.25 days. This however does not approximate the actual tropical year (e.g. based on the cycle of the seasons) close enough. Specifically the average year was slightly longer than it should have been (365.24219). So how bad is the Julian calendar? 365.25 - 365.24219 = 0.00781 days 0.00781 * 24 * 60 = 11.2464 minutes It was gaining about 11.2464 minutes per year. Hardly consequential - right? Well, that results in an increase of 1 day every 128 years or so. By now (2017) it would be 13 days out. Though after 46,766 years (or so) the Julian calendar would be correct again... Gregorian calendar The problem was (mostly) corrected with a new calendar introduced by Pop...