A critical investigation into the computations of Chinese and Indian calendars in early and high Tang China = 初盛唐中印曆術探論

Abstract

In 755 A.D., Buddhist monk and astronomer Yixing 一行 (683-727) was posthumously accused of plagiarism in the calendar he compiled by a few senior officials from the Astronomical Bureau and a son of Gautama Siddha (active in early eighth century), an Indian astronomer living in China who translated the Indian ephemeride Navagraha. This calendrical dispute resulted in victory of the Chinese over the Indian calendars. The latter henceforth dissipated from scholarly attention in China, leading to a dismissal of learning Indian astronomy.

This thesis compares the computational methods behind four types of ephemerides. Three of them were compiled between the seventh and the eighth centuries: Linde 麟德 Calendar by Li Chunfeng 李淳風 (602-670) of early Tang, Dayan 大衍 Calendar by Yixing during the Kaiyuan era and Navagraha translated into Chinese by Gautama Siddha. The fourth type contains some major ehpemerides compiled in India before 7th century A.D.

Five dimensions of computational methods are discussed in this thesis: 1) coordinate system; 2) epoch; 3) measurement and calculations of shadow of gnomon; 4) tables of sines and tangents; and 5) precession. Observational instruments and mathematical techniques such as trigonometry and interpolation method are also investigated.

By comparing the four types of ephemerides in terms of their computational methods, as well as mathematical techniques, observational instruments and cosmological views, this thesis reveals some possible reasons behind the calendrical dispute of Yixing.

As the translation of Navagraha was lost for almost 300 years after the Yuan dynasty, this thesis also includes a survey on the editions of Navagraha. (265 words)