Century leap year was introduced in 1582, but was adopted by various countries over several centuries, with the result that some countries still used the older Julian calendar while others used the Gregorian calendar. Dates prior to 1582 are generally calculated using the Julian calendar, and different countries have different conventions about dates between 1582 and their adoption of the Gregorian calendar. (See, for example, Old Style and New Style dates.) Century leap year In the Gregorian calendar, a year ending in "00" that is divisible by 400 is a century leap year, with the intercalation of February 29 yielding 366 days instead
Leap year be kept holy and the feast days and Sabbaths. Years consisting of 12 months have between 353 and 355 days. In a ("in order") 354-day year, months have alternating 30 and 29 day lengths. In a ("lacking") year, the month of Kislev is reduced to 29 days. In a ("filled") year, the month of Marcheshvan is increased to 30 days. 13-month years follow the same pattern, with the addition of the 30-day Adar Alef, giving them between 383 and 385 days. The observed and calculated versions of the Islamic calendar do not have regular leap days, even though both have