Lixiang kaocheng 曆象考成

The book (Yuzhi) Lixiang kaocheng (御製)曆象考成 is part of a collection called (Qinding) Lüli yuanyuan (御定)律曆淵源 "(Imperially endorsed) Origins and foundations of musical tuning, calculation, and the calendar". It consists of three treatises on astronomy, mathematics, and music that assemble Chinese and Western knowledge in these three fields. It was compiled on imperial order during the Kangxi reign-period 康熙 (1662-1722) under the supervision of Prince Yūn Lu (Ch. Yunlu 允禄, 1695-1767). The main compilers were He Guozong 何國宗 (d. 1767) and Mei Gucheng 梅瑴成 (1681-1764).

The Emperor's aim to have this book compiled was that he had become aware that the Jesuit missionaries who worked as astronomers at the imperial court brought knowledge that covered issues which Chinese scientists had never asked about. The concrete occasion was that the Directorate of Astronomy (qintianjian 欽天監) had made an error in the calculation of the solar term Xiazhi 夏至 (see calendar). The Kangxi Emperor therefore ordered the Director of Astronomy to make use of Western calculation methods that "did not fail in any salient point" (da dun bu wu 大端不誤).

The work at the collection was begun in 1713 and finished in 1722. It was printed by the Imperial Printing Shop in 1724. The whole collection has a length of 100 juan and consists of the parts Lixiang kaocheng 曆象考成 (42 juan), Lülü zhengyi 律呂正義 (5 juan), and Shuli jingyun 數理精蘊 (53 juan).

The Lixiang kaocheng consists of two parts (bian 編) and an appendix with tables with a length of 16 juan. The first part serves as an overview, begins with a general discussion on the principles of the calendar, and then explains individual themes like celestial phenomena, the conditions of the earth, the calendar, the ecliptic, the celestial equator, the system of celestial coordinates and the precession.

The second part discusses the calculation of the movement of celestial bodies and time, including the path of the Sun, calendar calculations based on moon phases, lunar eclipses, methods for predicting solar eclipses, and calendar calculations involving the movements of the five planets and the positions of the starry constellations.

The Lixiang kaocheng is a concise book on all important matters of time calculation based on the movements of the planets and the stars. In this shape, it assembles modern knowledge from Chinese tradition and Western expertise, as transmitted by Jesuit astronomers, but only in a practical way, and it wholly neglects theoretical discussions about the solar system. The calculations are mainly based on Tycho Brahe's (1545-1601) solar system and therefore somewhat outdated. For this reason the Qianlong Emperor 乾隆帝 (r. 1735-1796) had the 10-juan-long treatise Lixiang kaocheng houbian 曆象考成後編 compiled that fills some gaps in the collection.