1231-1316

Chinese astronomer, mathematician, and hydraulic engineer best known for preparing the Shoushi calendar, which is equivalent to the modern Gregorian calendar. Kublai Khan entrusted Kuo Shou-ching with the regulation of China's irrigation and waterways in 1271. He was then instructed to reform the calendar, which he completed by 1280. His efforts involved designing an observatory and sophisticated astronomical instruments that he used to observe the Sun, the 28 xiu (lunar lodges), and many unnamed stars.