Calendar year ("leap days" or "intercalary days"). The Gregorian year, which is in use in most of the world, begins on January 1 and ends on December 31. It has a length of 365 days in an ordinary year, with 8,760 hours, 525,600 minutes, or 31,536,000 seconds; but 366 days in a leap year, with 8,784 hours, 527,040 minutes, or 31,622,400 seconds. With 97 leap years every 400 years, the year has an average length of 365.2425 days. Other formula-based calendars can have lengths which are further out of step with the solar cycle: for example, the Julian calendar has an average
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