A STUDY ON THE TERM FOR THE LUNAR NODES IN MEDIEVAL EAST ASIAN ASTRONOMICAL ALMANACS -FOCUSING ON THE TRANSITIONAL PERIOD WHEN THE SHIXIAN CALENDAR WAS ESTABLISHED-
In the traditional East Asian astronomical–calendrical system, the lunar nodes were termed Jeong-gyo(正交) and Joong-gyo(中交), conventionally referring to the descending and ascending nodes respectively, with Jeong-gyo used as the computational starting point. In the late Ming dynasty of China, the introduction of Western astronomy and the formation of the Shixianli(時憲曆) system generated conceptual confusion, as the Western method of measuring the degree from the ascending node to the Moon is incompatible with the term of Jeong-gyo, because Jeong in the term means staring point. Through an analysis of pre-Shixianli calendrical treatises, this study demonstrates that the correspondence between Jeong-gyo and Nahoo(羅睺), and between Joong-gyo and Gyedo(計都), was long maintained, and that although the Ming translation of the Islamic calendrical system, the Huihuili(回回曆), employed only Nahoo and Kyedo, their meanings remained unchanged. By comparing the longitude of Jeong-gyo in the lunar mean-motion tables of the three major Shixian li treatises with modern astronomical calculations, this study shows that Jeong-gyo corresponds to the descending node in the Chongzhen Lishu(崇禎曆書) but to the ascending node in the Lixiang Kaocheng(曆象考成) onward. This shift reveals a transitional confusion state and the correspondence between Jeong-gyo and Nahoo was gradually dismantled. These findings clarify the transitional redefinition of calendrical terminology in the process of assimilating Western astronomy.