The eclipse of 21 June 1629 in Beijing in the context of the reform of the Chinese calendar

This paper examines the predictions made by Chinese, Muslim and Jesuit astronomers of the eclipse occurred in 21 June 1629, allegedly the event that determined Emperor Chongzhen’s resolution to reform the calendar using the Western method. We have compared these predictions, as reported at the time by the Chinese scholar and convert Xu Guangqi, and, in order to establish their accuracy, we have compared them with an accurate reconstruction of the eclipse made by NASA. In contrast with current opinions, the paper argues that the prediction made by the Jesuits was indeed the most accurate. Although not overwhelmingly accurate, it was indeed instrumental in dissipating Chongzhen’s doubts about the need to entrust Jesuit missionaries serving at the Chinese court with the task of reforming the calendar, leading to the first important scientific exchange between Europe and China.