宋历步交会术中“三差”的计算方法

THE CALCULATING METHODS FOR QI CHA, KE CHA AND SHI CHA IN FORECASTING SOLAR ECLIPSE IN THE CALENDARS OF THE SONG DYNASTY

中国古代在预报日食时,为把实白道上月去交度换算为视白道去交度,使用气差和刻差等。在由定朔推算食甚时刻时,使用时差。经过不断尝试,"三差"的计算方法在宋代基本定型。

Qi Cha and Ke Cha were used to change the distance between the moon and the node of the ecliptic and the lunar orbit on Moon's path into that on apparent Moon's path in the Chinese ancient methods for forecasting the solar eclipses. Shi Cha was used to calculate the time of (?) e middle of eclipse from true new moon. Through uninterruptedly attempting, the methods for the three Chas basically fell into a pattern in the Song Dynasty.