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The Scientific Accomplishments of Ancient China’s Guo Shoujing

Published: August 12, 2022
Guo Shoujing, a noted astronomer, mathematician, and engineer of China’s Yuan Dynasty. (Illustrated by Ilnar Karim)

With an asteroid and a lunar crater named in his memory, there is no doubt that Guo Shoujing’s legacy was remarkable to posterity. Raised and inspired by his grandfather to study mathematics, astronomy, and hydraulic engineering, Guo became one of ancient China’s most accomplished scientists. 

Guo Shoujing (郭守敬, 1231–1316) lived during the Yuan Dynasty and was particularly curious as a child. When he was only fourteen, he designed a bronze water clock for a local observatory which he called “Lotus Clepsydra” given the lotus shape of the artifact into which the water dripped. 

By the age of 16, Guo was studying mathematics and at the age of 20 he was already involved in a hydraulic project as a state engineer. 

A considerate engineer

Guo was known for his persistent character and unbridled imagination. Shining for his humility and willingness to learn from others, he always strived to improve his work and challenge the existing methods. Kublai, Mongol emperor and founder of the Yuan dynasty, was quick to perceive Guo’s potential, and consequently appointed him as the official in charge of rivers and reservoirs.

Within a short time, Guo made significant improvements to the irrigation systems. The story goes that, on one occasion, a region in the northwestern part of the empire suffered from food shortages due to congested river flows. Using his engineering knowledge and diligent effort, Guo cleared and expanded the irrigation system, thus solving the problem. Following this heroic feat, Guo was assigned the responsibility of protecting the nation’s freshwater environments.

Guo also ventured to modify the existing canal network by deepening the existing canal and building a new one from north to south. After conducting extensive field surveys and convincing court officials to support the project, the ingenious scientist optimized the transportation of food supplies and made it possible for the capital, Beijing, to receive the goods directly. 

Creating a calendar for Eurasia

In the absence of a system that could accurately illustrate ground levels on maps, Guo took the initiative to conduct topographic surveys and create a method for indicating cartographic altitudes. However, his years as a skilled inventor were just beginning. 

In 1276, as the Mongol Empire continued to expand across Eurasia, Kublai realized that the different calendars of the conquered nations often caused confusion throughout the land. He therefore turned to his trusted official, Guo, and asked him to create a reliable calendar that could provide universally accurate information for agriculture and, at the same time, unify the expanding kingdom. 

To this end, Guo established some 26 measuring points throughout the Empire. With the help of 14 officials, Guo collected measurements and observations from all districts, while improving existing astronomical instruments, and sometimes inventing new ones.

After four years of hard work, Guo and his team succeeded in creating an unusually accurate calendar with a time lag of only 26 seconds from the Earth’s actual revolution around the Sun. The new calendar — commonly known as the Season-Granting Calendar or Shoushi Calendar — was put into use for the next 363 years and served as a tool for emperors to conduct imperial celebrations and ceremonies in accordance with heavenly phenomena. 

On account of his contributions to the empire, Guo was the only Yuan Dynasty government official asked to remain in office past the age of 70. He lived to the age of 86, and is remembered today for creating a system of exact dates that allowed Chinese scholars of the era to record their history with unprecedented accuracy. His diligence and unceasing desire to learn made him a model for posterity of sound practical scholarship and devotion to his nation.