Shoushi Calendar
《授时历》
Shoushi Calendar，the most outstanding calendar in ancient China，was compiled by Guo Shoujing，a prominent scientist in the Yuan Dynasty，and his colleagues. Enforced in 1281,throughout the Ming Dynasty and the begin-nin4 of the Qinq Dynasty，the calendar was used for over 360 years.
《授时历》是中国古代最优秀的历法。由元代著名科学家郭守敬等人编制，从1281年开始实行，历经整个明代，一直到清初，共用了360多年。
The reason why the calendar was used for such a long time has much to do with its accuracy in calculation. In the first place，it employed astronomical docu-ments of the highest accuracy in its time. For instance，it set the tropical year at 365.2425 days，which was the exactly the same as that in the currently used Gre-gorian Calendar, 301 years preceding the latter though. Secondly, based on earlier scholars finding that the length of the tropical year was gradually shortening，the Shoushi Calendar held that the tropical year shortened by 0. 0001 day every 100 years，which was more accurate as compared with earlier researches.
《授时历》之所以沿用这么长时间，和它的计算精度非常高有很大关系。首先，它使用了当时最为精确的天文资料。例如，它确定了回归年的长度为365.2425日，与现今通行的公历值完全一致，但是它比格里高利历早了301年。其次，它吸收了前人研究发现的回归年的长度在逐渐变小的观点，规定100年中回归年的长度减小0. 0001日。与前人研究相比，这个数值要精确一些。
In addition，instead of the mathematical method of recording astronomical documents via complicated fractions，the calendar employed decimal fractions，which largely reduced calculation workload and guaranteed accuracy. It also made innovations in terms of calculation methods;for instance，the use of mathematical approaches like cubic interpolation，polynomial equations to the 4th order and spherical trigonometry.
另外，《授时历》废除了用复杂分数表示天文资料的办法，使用小数制，不仅大大减少了计算量，也保证了计算精度。《授时历》在计算方法上也有创新，例如三次插内插法、四次多项式方程、球面三角法等数学方法的使用。
Soon after its compilation，the Shoushi Calendar was Spread to and adopted by Japan and Korea. In recent years，astronomers from Japan，European and North American countries are again showing interests in ahe Shoushi Calendar，and some broad and in-depth researches have been made. As an advanced and accurate calendar in the history of China，the Shoushi Calendar also occupies a distinct posi-tion in the history of world astronomy.
《授时历》编制不久即传播到日本、朝鲜，并被采用。近年来日本和欧美等国的天文学家对《授时历》产生了新的兴趣，进行了广泛而深入的研究。作为中国历史上一部先进的、精确的历法，《授时历》在世界天文学史上也占有突出的位置。