Mid-year Intercalation:the Importance of the Pre-Qin Calendar History Reform

In the pre-Qin Dynasty in ancient China,there were six calendar.Summer calendar is mid-year intercalative. Calendar recorded in the Shang Oracle is a transition from year-end intercalation to mid-year intercalation.In the beginning, year-end intercalation was used and there were 13 months.After the reform,year-end intercalation was adopted. Calendar in the Zhou Dynasty practiced year-end intercalation,but it also adopted March-intercalation for some time. But the reform was criticized and eventually failed.Zhuan Xu Lipracticed year-end intercalation until the Han Dynasty. At the beginning of the Han Dynasty,calendar was reformed and then the 24 solar terms were clear and concrete. Since then in all the Chinese lunar calendar,leap month is the one without mid-solar term.Therefore the issue of arranging intercalation is solved.