Title

A Study on the Theory of Solar Eclipse in the Dayan Li

Author

Min Yuan  Anjing Qu

Genre

Article  

Pages

159-173

Download

PDF

Language

Chinese

Key words

Yi-xing, lunar parallax, the Dayan li, solar eclipse

Abstract

   In his Dayan li (724 AD), Yi-xing designed a new algorithm for calculating articles related with the solar eclipse, which is a full-scale reformation after Zhang Zixin discovered the influence of solar eclipse computations caused by the lunar parallax. In his calendar, Yi-xing considered modifying factors such as the longitude of the sun， the relative position between the sun and the moon at the middle of solar eclipse, and the latitude at the place of the observer. On the basis of reading and analyzing original texts of the Dayan li, this article discusses the method how to construct the algorithm for judging when the solar eclipse will happen and for calculating the magnitude of the solar eclipse. The algorithm for calculating the deviation caused by the lunar parallax at the middle time of the solar eclipse in different places, namely Jinfu Shicha, is explained by a view of a geometrical angle. The Shicha algorithm shows that it was equivalent to a theoretical model when the hour angle of the sun h=0. These characteristics of algorithms can offer a correct interpretation of the shicha algorithm after Yi-xing.