Calendar world for civil purposes. It is a purely solar calendar, with a cycle of leap days in a 400-year cycle designed to keep the duration of the year aligned with the solar year. Each Gregorian year has either 365 or 366 days (the leap day being inserted as 29 February), amounting to an average Gregorian year of 365.2425 days (compared to a solar year of 365.2422 days). It was introduced in 1582 as a refinement to the Julian calendar which had been in use throughout the European Middle Ages, amounting to a 0.002% correction in the length of the year.
Chinese calendar (, 29 days); stem branches for the first, eleventh, and 21st days, and the date, stem branch and time of the solar terms. The traditional Chinese calendar was developed between 771 and 476 BC, during the Spring and Autumn period of the Eastern Zhou dynasty. Before the Zhou dynasty, solar calendars were used. One version of the solar calendar is the five-elements calendar (), which derives from the Wu Xing. A 365-day year was divided into five phases of 73 days, with each phase corresponding to a Wu Xing element. A phase began with a governing-element day (), followed by