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.
《授時歷》
《授時歷》是中國古代的一種精確歷法。1276年，元世祖忽必烈（1215—1294）要求許衡（1209—1281）與郭守敬（1231—1316）、王恂（1235—1281） 共同研訂新歷法。為了編纂新歷法，他們在全國范圍內進行大規模天體測量，為修訂歷法提供精確數據。1280年，新歷法編成， 忽必烈將其取名為《授時歷》，自1281年起頒行使用。
《授時歷》打破了古代制歷的傳統，第一次把小數引入歷法，以365.2425日為一回歸年，與地球環繞太陽公轉一周的實際時間僅差25.92秒，其精度與現行世界通用的公歷相當，比西方早300多年，反映了當時中國天文歷法的新水平。《授時歷》是中國古代最先進、最精確、使用時間最長的歷法，也是當時世界上最先進的一部歷法，曾傳播至日本、朝鮮、越南及歐洲等地，對當地的歷法產生了深遠影響。
