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
Mesoamerican calendars ruled the following thirteen days. If the first day of a trecena was auspicious then so were the next twelve days. This 365-day calendar corresponded was divided into 18 'months' of 20 days each, plus 5 'nameless' days at the end of the year. The 365 day year had no leap year so it varied from the solar year by a quarter of a day each year. The years were given their name in much the same way as the days of the 260-day calendar, 20 names were paired with 13 numbers giving 52 different possibilities for year names In