Guo Shoujing's Shoushi Li and the Joseon Chiljongsan-Naepien

The Shoushi Li of the Yuan dynasty is well known as an outstanding calendar based on precise observations and newly invented mathematical methods.It was to become the basis of the compilation of the Ming(1368—1643)Datong Li and Joseon(1392—1910)Chiljongsan-Napion.The Chiljongsan-Naepion was one of the most important astronomical achievements of King Sejong's reign(1418—1450).Based on the Huihui Li,it was published in 1444 together with the Chiljongsan-Oepion.It adopted the epoch,astronomical constants and the computational methods of the Shoushi Li,while the value of yingshu was adopted from the Datong Li published 1368 by Liu Ji.The addition of the calculation of "Four Imaginary Stars"(siyu)to the chapter on pacing and constants used in calculation of eclipses were those given in the Datong Li Tonggui published in 1384 by Yuan Tong.It is considered that the Chiljongsan-Napion drew on the best points of both calendars.