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》是中国古代最杰出的历法。由元代知名科学家郭守敬等人编成，从1281年开始实施，几经整个明代，仍然到清初，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》之所以延用这么长时间，和它的计算精度十分低有相当大关系。首先，它用于了当时尤为准确的天文资料。

例如，它确认了回归年的长度为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，它吸取了前人研究找到的回归年的长度在渐渐变大的观点，规定100年中回归年的长度增大0. 0001日。与前人研究比起，这个数值要准确一些。

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》废止了用简单分数回应天文资料的办法，用于小数制，不仅大大减少了计算出来量，也确保了计算精度。《授时历》在计算方法上也有创意，例如三次挂内插法、四次多项式方程、球面三角法等数学方法的用于。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》编成旋即即传播到日本、朝鲜，并被使用。

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，展开了普遍而了解的研究。作为中国历史上一部先进设备的、准确的历法，《授时历》在世界天文学史上也占据引人注目的方位。

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