Guo Shoujing

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Guo Shoujing (Chinese: 郭守敬; pinyin: Guō Shǒujìng; Wade-Giles: Kuo Shou-ching) (1231 – 1316) was a Chinese astronomer, engineer, and mathematician. His grandfather was Guo Yang, a noted scholar. By the age of fourteen Guo Shoujing designed a water clock and at sixteen he was studying mathematics. He worked on improving the Chinese gnomon and worked at Kublai Khan's observatory. There he formulated the Shoushi calendar and calculated the year to be 365.2425 days. This is the same as the Gregorian calendar, but almost three centuries earlier. It would be used for the next 364 years. He also did work relating to spherical trigonometry.

He is a famous ancient Chinese hydraulic engineer and mathematician. He improved the calendar and was off by only 50 seconds. He calculated a year was 365 days 5 hours 36 minutes and 11 seconds. Although he did a great deal on the modern calendar, he suggested pi 3, unlike Zu Chongzhi's 3.14159265 and Zhang Heng's 3.142.

In engineering he is best known for constructing the artificial Kunming Lake in Beijing as a reservoir and part of a new waterway for grain transport.

Asteroid 2012 Guo Shou-Jing named after him.