Guo Shoujing

Guo Shoujing (1231-1316) was a Chinese astronomer, engineer and mathematician who served the Yuan dynasty court of Kublai Khan. He led a major imperial project to reform the Chinese calendar, producing the Shoushi calendar of 1281, which calculated the length of the tropical year to within about 26 seconds of its modern measured value, among the most accurate calendars devised anywhere before the modern era. He designed and built new, more precise astronomical instruments, including a simplified armillary sphere, and directed extensive water control engineering projects, including canal systems supplying the Yuan capital at Dadu, present day Beijing. His combination of precise instrument design and systematic observational campaigns across the empire allowed the calendar reform to draw on far more accurate data than earlier Chinese calendrical work.