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
Zoroastrian calendar Zoroastrian Seasonal-Year Society. In 1906, the society published its proposal for a Zoroastrian calendar which was synchronised with the seasons. This "Fasli" calendar, as it became known, was based on the Jalali calendar introduced in 1079 during the reign of the Seljuk Malik Shah and which had been well received in agrarian communities. The Fasli proposal had two useful features: a leap-day once every four years, and harmony with the tropical year. The leap-day, called "Avardad-sal-Gah" (or in Pahlavi: "Ruzevahizak"), would be inserted, when required, after the five existing "Gatha" days at the end of the year. New Year's Day