A distinctive feature of the Imperial Chinese state was that for much of its existence successive emperors maintained staffs of official astronomers. The responsibilities of those officials included the annual production of a complex luni-solar calendar, the accuracy of which was seen as an important element in imperial prestige, and also the prediction of events such as solar and lunar eclipses. They were also responsible for recording observations of celestial phenomena and providing advice on their significance for the conduct of the imperial government. Since these astronomers held posts in the civil service, their activities generated large volumes of documents that were preserved in official files. China is therefore unique in the richness of the material from past centuries available to historians of astronomy. Imperial astronomers based their calculations on mathematical methods and tabulated data set out in officially approved texts known as li 曆 ‘[astronomical] systems’. It was common for a new dynasty to introduce a new astronomical system, but improvements also might be made during the reign of a dynasty. 

After surveying the tradition of imperial astronomy in the long term, this talk will turn to a more detailed examination of some events which may be taken to illustrate a number of aspects of imperial astronomy in China. In the early 17th century, at the start of the last half-century of the rule of the 明Ming dynasty (1368-1644) in China, there was a widespread sense that the time had come for a major reform of the dynasty’s official astronomical system, the Da tong li 大統曆 ‘Great Concordance system’. This system was a modification of the Shou shi li 授時曆 ‘Season-granting system’, created by Guo Shoujing 郭守敬 (1231–1316) and adopted as the official astronomical system by the Yuan 元 dynasty in 1280. Its content was therefore effectively nearly four centuries old, and the predictions of the system were becoming inaccurate. Around that time, a number of Jesuit missionaries arrived in China; all of them had acquired a basic knowledge of astronomy and mathematics during their training as members of the Jesuit order, and some had more advanced skills in these fields. The high official Xu Guangqi 徐光啓 (1562-1633), himself a convert to Catholicism, successfully petitioned the Chongzhen 崇禎 emperor (r. 1627-1644) to establish a Li ju 曆局 (office for astronomical systems) in which Jesuit experts would work with Chinese colleagues to construct a new astronomical system structured on Chinese lines, but drawing on European astronomical techniques. The Li ju began its activities in 1629, and continued work until the fall of the dynasty in 1644. The best known aspect of the work of the Li ju is the compilation of the series of methodological texts and tables of data setting out the new astronomical system, which form the major part of the book Chong zhen li shu 崇禎曆書 ‘Texts on astronomical systems [compiled during] the Chongzhen reign’. But the work of the Li ju went well beyond that. This talk will give an overview of the archival sources, which show that for nearly two decades the staff of the Li ju constructed instruments, made predictions, and conducted observations, which on occasion were made during expeditions to sites some distance from Beijing. These other activities generated a large number of documents, many of which have been preserved in historical sources. This talk will review representative examples of these activities, with the aim of giving a rounded picture of what the Li ju accomplished during the nearly three decades of its existence.