Absence of Geometric Models in Medieval Chinese Astronomy

In 718 A.D., Ch’üt’an Hsi-ta (Gautama Siddhārtha), an Indian astronomer who was appointed an“astronomer royal” in the T’ang court compiled a compendium of omens and divinations, called K’aiyüan Chan-ching, analogous to Varahamihira’s Br .hatsam. hita. The 104th volume of this work, Chiu-chih li (Nine Upholders Calendrical System) on astronomy was entirely based on the Indian astronomy of the 7th century which in turn was based on the geometric astronomy of the Greeks. A few years later, the emperor asked I-hsing (Yixing in pinyin), a buddhist monk, an astronomer and a mathematician, to overhaul the traditional Chinese astronomy. He submitted an astronomical system, called Ta-yen li (Grand Expansion Calendrical System, Dayan li in pinyin) in 727 A.D. Only Ta-yen li was officially adopted. In the 13th century, a Persian astronomer submitted to Khubilai Khan an astronomical system, Myriad Year Calendrical System, based on the geometric Islamic astronomy. This too was not officially adopted. Instead, Khubilai Khan ordered a major reform of the traditional Chinese system. The result was Shou-shih li (Granting the Seasons Calendrical System) which held sway over the Chinese astronomy until the arrival of the Jesuits in the 17th century. An analysis of the motion of the Sun and and the lunar parallax in Ta-yen li and Shou-shih li shows how little impact foreign imports had on Chinese astronomy. Geometric methods began to make inroads in Chinese astronomy only after the arrival of the Jesuits in the 17th century.