Century leap year thus the leap day February 29 in those years always falls on a Tuesday (dominical letter BA). The Gregorian calendar yields an average year that currently tracks the annual revolution period of the Earth more closely than the older Julian calendar, in which every fourth year (including end-of-century years) is a leap year. The Julian formula adds too many leap days (3 every 400 years), causing the Julian calendar to drift gradually with respect to the astronomical seasons. Over time, natural events such as the spring equinox began to occur earlier and earlier in the Julian calendar. The Gregorian calendar
365-day calendar length of 365 days with no rule for leap days, despite potential leap year rules being acknowledged by the 9th century at the latest. In particular, of the versions still in use today the Qadimi version does not have any form of leap rule; the Shahanshahi version had one leap month added in the 12th century but no leap years since, while the Fasli version (introduced in the 20th century) adds one day every four years. 365-day calendar A 365-day calendar consists of exactly 365 days per year (no leap days), and is primarily used in computer models and as