Tai Chu Calendar: China's First Complete Calendar

In its barest term, a calendar is a system showing the days, weeks, and months of a particular year. As agricultural activities are closely related to seasonal changes, in the very beginning the calendar was created to meet the demand of agricultural production. China, with a long history of agricultural production, boasted many calendars in ancient times, among which the Tai Chu Calendar was the first relatively complete calendar.

In its early years, the Western Han Dynasty (206BC-24AD) continued to use the Zhuan Xu Calendar of the Qin Dynasty (221-206BC), which had come errors. Then in 105 BC, Emperor Wudi, advised by the famous historian Sima Qian, ordered the calendar revision. A year later, Luo Xiahong and Deng Ping, among others, made the Tai Chu Calendar.

According to the new calendar, a year had 365.2502 days and a month 29.53086 days, and the beginning of a new year was changed to January rather than October. Besides, the new calendar adopted the 24 solar terms, which were useful for the farming season. Based on the results from celestial measurement and records by court astronomers, the Tai Chu Calendar also worked out the cycle of solar eclipse - 135 months.

The first relatively complete calendar in China, the Tai Chu Calendar was also the most advanced of its kind in the world at its time and was used for a period of 189 years after its inception.