조선의 回回曆法 도입과 『칠정산외편』

Abstract

A set of books on the Islamic calendar system was translated into Chinese during the reign of the first Ming emperor, and published under the title of Huihui lifa (回回曆法). However, the Chinese version of the Islamic system contained numerous errors and omissions in the beginning stages of astronomical calculations. Nevertheless, Joseon’s astronomers Yi Soonji and Kim Dam were successful in overcoming the mistakes included in Huihui lifa. Corrections and additions were made to bring the incomplete Chinese-Islamic system to a fully-equipped Korean version, entitled Chiljeongsan oepyon (七政算外篇). In this paper, aspects of the revisions of Huihui lifa carried out by King Sejong’s astronomers were investigated in detail. Explanations in depth were given to the procedures how the omitted expression for the time interval in the Islamic lunar calendar between a given day and the new epoch was supplemented and how the initial errors in position calculations of the heavenly bodies (due to the erroneously defined epoch) were corrected. The role of Yuan Tong’s Weidu taiyang tongjing (緯度太陽通徑) during the Korean modification on Huihui lifa was also surveyed. By comparing recent numerical analyses by other researchers, the reason why the eclipse predictions for Seoul by Chinese-Islamic Chiljeongsan oepyon had been better, in general, than that by Chinese-traditional Chiljeongsan naepyon (七政算內篇) was pursued too.