In the thirteenth century, the Mongols established a large contiguous land empire across Eurasia, where cross-cultural contact flourished at an unprecedented scale. For example, a Chinese calendar (lunisolar calendar) was first described in a zīj (astronomical handbook with tables) in this period.

In this paper, I shall deal with a chapter concerning a Chinese calendar in the Zīj-i Īlkhānī by Naṣīr al-Dīn Ṭūsī (1201–1274). So far, in academia, this calendar has been called the ‘Chinese-Uyghur’ calendar, but I shall argue that this title is not necessarily accurate and that the Uyghurs, who had political and cultural importance in the nascent period of the Mongol empire, were not involved in compiling this calendar. Rather, this calendar was directly brought from China proper by a Chinese Taoist master who accompanied his Mongol ruler.

This Chinese calendar, written in Persian, gives us a unique firsthand view into a civil Chinese calendar. We can find few sources on this topic in China now. Furthermore, this civil-form calendar has several elements in common with the Shou shi li (授時暦), the official calendar of the Yuan dynasty (1271–1368), distributed from 1281 sometime after the compilation of the Zīj-i Īlkhānī. By looking at the flow of astronomical knowledge from the civil calendar to the official one through research on the Chinese calendar in the Zīj-i Īlkhānī, we perceive a ‘productive’ relationship between the official and civil spheres in the astronomical field in China. This is despite the fact that some scholars have argued that activities relative to astronomy, and calendar making in particular, were restricted to the official realm in Chinese dynasties. A thousand miles away from China, in Iran, the Zīj-i Īlkhānī preserves the form of a civil calendar that has been lost in China itself.