《明天历》岁差与上元积年

On Precession and the Superior Epoch in the Mingtian Li

岁差常数是中国古代传统历法中推算太阳运动的重要常数之一,通常是附会上元积年而获得,但北宋周琮《明天历》却另辟他法。文章通过对《明天历议》术文的解读分析,发现并复原了周琮利用月亮运行速度确定岁差常数的新方法,证实了其岁差常数是独立于上元积年而确定的;同时,重新考察了《明天历》上元积年的选取过程,结果表明《明天历》岁差常数反而参与了上元积年的确定,这与以往岁差常数附会上元积年的传统完全不同,从而完善了对中国古代历法天文常数系统特征的认识。

Precession(Suicha岁差)is one of the most important constants in the ancient Chinese calendar.It was normally determined by the method High Epoch Accumulated Years(Shang yuan ji nian上元积年),but in the Northern Song dynasty Zhou Cong designed a new method to calculate it.This paper analyses the related content in the Mingtian Li Yi,uncovering Zhou Cong’s new way to determine Precession by the speed of the moon,and confirms that Precession is independent of the High Epoch Accumulated Years.We also reconsider the procedure to determine the High Epoch Accumulated Years in Mingtian Li,the results indicating that though the Precession was involved in the process of calculating the High Epoch Accumulated Years,this was completely different to the previous way that High Epoch Accumulated Years had been used to calculate the Precession.Thus,this article improves our understanding of the features of the astronomical constant system of ancient Chinese calendars.