Shoushi Calendar
The Shoushi Calendar was an accurate calendar in ancient China. In 1276, Kublai Khan (1215-1294), the first emperor of the Yuan Dynasty (1206-1368), tasked Xu Heng (1209-1281), Guo Shoujing (1231-1316) and Wang Xun (1235-1281) with creating a more precise calendar. To this end, these astronomers conducted nationwide observations to gather accurate data for the new calendar. By 1280, the calendar was completed and Kublai Khan named it the Shoushi Calendar, which came into use in 1281.
The Shoushi Calendar was groundbreaking in its adoption of a decimal time system. The system determined that the length of the tropical year was 365.2425 days, only 25.92 seconds off from the current measurement of a year. This level of accuracy is comparable to the widely used Gregorian Calendar, but the Shoushi Calendar was developed over 300 years earlier. The Shoushi Calendar is regarded as the most advanced, accurate, and long-lasting calendar in ancient China. It was also considered the most advanced calendar in the world at that time. Its influence extended far beyond China, as it spread to countries and regions such as Japan, Korea, Vietnam, and Europe, where it had a profound effect on their respective calendars.
《授时历》
《授时历》是中国古代的一种精确历法。1276年，元世祖忽必烈（1215—1294）要求许衡（1209—1281）与郭守敬（1231—1316）、王恂（1235—1281） 共同研订新历法。为了编纂新历法，他们在全国范围内进行大规模天体测量，为修订历法提供精确数据。1280年，新历法编成， 忽必烈将其取名为《授时历》，自1281年起颁行使用。
《授时历》打破了古代制历的传统，第一次把小数引入历法，以365.2425日为一回归年，与地球环绕太阳公转一周的实际时间仅差25.92秒，其精度与现行世界通用的公历相当，比西方早300多年，反映了当时中国天文历法的新水平。《授时历》是中国古代最先进、最精确、使用时间最长的历法，也是当时世界上最先进的一部历法，曾传播至日本、朝鲜、越南及欧洲等地，对当地的历法产生了深远影响。
