Chinese Calendar - Number of Days

Number of Days

In the late Spring and Autumn Period (722–481 BC), the former Sifen calendar (古四分历) was established, and set the tropical year at 365.25 days, the same length as the Julian calendar which was introduced in 46 BC. The Taichu calendar (太初历) of 104 BC under Emperor Wu of Han rendered the tropical year at roughly the same (365 ).

Many other calendars were established between then and the Yuan Dynasty (1271–1368), including those established by Li Chunfeng (602–670) and Yi Xing (683–727). In 1281, the Yuan astronomer Guo Shoujing (1233–1316) fixed the calendar at 365.2425 days, the same as the Gregorian calendar established in 1582; this calendar, the Shoushi calendar (授時曆), would be used in China for the next 363 years. Guo Shoujing established the new calendar with the aid of his own achievements in spherical trigonometry, which he derived largely from the work of Shen Kuo (1031–1095) who established trigonometry in China.