What is the main contribution of Guo Shoujing, a scientist in Yuan Dynasty?

Compile a "time calendar" and manage the water system.

Guo Shoujing (1231-1316), an astronomer, mathematician, water conservancy expert and instrument manufacturing expert in Yuan Dynasty, was born in Xingtai, Shunde (now Xingtai, Hebei). In order to compile the calendar, he successively created and improved more than a dozen astronomical instruments and meters, such as Gao Biao, Hou Ji, Jane, Huntianyi, Li Yunyi, Jingfu, Yeung Yi and Peeping, which took a long time.

In compiling the calendar, Guo Shoujing and Nepalese architect Anica built a stargazing platform in Beijing, which contained advanced astronomical instruments made in Guo Shoujing. There are two main astronomical observation methods for making calendars. One is to measure the exact time of the 24 solar terms, especially the winter solstice and summer solstice. The instrument used is a sundial. The other is to determine the position of celestial bodies, and the main tool used is the armillary sphere.

In terms of water control, Guo Shoujing has two great achievements, one is to control the Yellow River system, and the other is to create the capital water system. In less than a year, Guo Shoujing led migrant workers to repair the Tanglai Canal with a total length of more than 400 miles and the Han Yan Canal with a total length of more than 250 miles, as well as 10 main canals and 68 branch canals of different sizes, and successfully completed the task of river dredging and restoration. Water control in Guo Shoujing benefited Xixia Canal, and tens of thousands of hectares of farmland were irrigated in time.