The "Season-Granting Calendar" was a calendar compiled by the famous Yuan Dynasty scientist Guo Shoujing and others, a major achievement in ancient Chinese scientific history.
The "Season-Granting Calendar" set a year at 365.2425 days, which differs from the time it takes Earth to orbit the Sun by only twenty-six seconds. Based on this, it can be said that the precision of the "Season-Granting Calendar" is nearly identical to the globally used Gregorian calendar, yet it appeared more than three hundred years earlier than the current calendar.
In China, the "Season-Granting Calendar" was used for over 360 years, making it one of the longest-lasting calendars in Chinese history, and it played a huge guiding role in the daily production and life of the Chinese people. Additionally, the "Season-Granting Calendar" also spread to Korea and Vietnam, benefiting the local populations there.
Before the appearance of the "Season-Granting Calendar," the Chinese people had long used the "Daming Calendar" compiled by the renowned scientist Zu Chongzhi during the Northern and Southern Dynasties period. However, due to the technological limitations of that era and the passage of several hundred years, the "Daming Calendar" contained significant errors, which prompted the reigning Emperor Kublai Khan of the Yuan Dynasty to conceive the idea of creating a new calendar.
Starting from June 1276, Kublai Khan, the founding emperor of the Yuan Dynasty, successively ordered renowned Chinese scientists such as Wang Xun, Xu Heng, and Guo Shoujing to compile a new calendar. To this end, the imperial court established a total of twenty-six observation stations, conducting a series of tests across a vast region stretching over ten thousand li in length and six thousand li in width, consuming enormous human, material, and financial resources. After four years of hard work through all seasons, the new calendar was finally completed. Kublai Khan was very satisfied with the result and personally named it the "Season-Granting Calendar."
During the compilation of the Shoushi Calendar, Guo Shoujing's contributions were indispensable, to the extent that whenever later generations mention the Shoushi Calendar, his name is invariably brought up.
Guo Shoujing's grandfather, Guo Rong, was a man of vast learning, proficient in astronomy, mathematics, and water conservancy. Under his influence, Guo Shoujing developed a strong interest in science and mathematics from a young age. Guo Rong placed great importance on his grandson's education, not only teaching him knowledge from books but also often taking him into nature for hands-on activities, cultivating his observational and practical skills. This greatly benefited Guo Shoujing's future development. Later, Guo Shoujing was sent by his grandfather to study under his old friend Liu Bingzhong, where he met his lifelong close friend Wang Xun. In the compilation of the "Season-Granting Calendar," Wang Xun's contributions were also significant.
Soon after, Kublai Khan, having heard of Liu Bingzhong's profound expertise in the sciences, summoned him to Dadu (present-day Beijing). Guo Shoujing then shifted his studies to Zhang Wenqian, a close friend of Liu Bingzhong. As Zhang Wenqian was dispatched to various regions as a local official, Guo Shoujing remained by his side throughout. Zhang Wenqian often took him along to survey local terrain and construct water conservancy projects. Two years later, convinced that Guo Shoujing was ready to strike out on his own, Zhang Wenqian recommended this outstanding student of his to Kublai Khan.
When Guo Shoujing first met Kublai Khan, the founding emperor of the Yuan Dynasty, he presented six proposals for water conservancy projects. The emperor greatly praised him and immediately appointed him as an official in charge of water management at court.
Two years later, Kublai Khan, the founding emperor of the Yuan Dynasty, sent Zhang Wenqian and Guo Shoujing to the former territory of the Western Xia to build water conservancy projects and restore local agricultural production. Guo Shoujing constructed numerous dams there and dredged canals to facilitate farmland irrigation. Kublai Khan was quite pleased with this, and after Guo Shoujing returned to the capital, he was dispatched by the emperor to various regions to build water conservancy projects.
After the fall of the Southern Song Dynasty, the Yuan Dynasty had largely unified China, and it was at this time that Kublai Khan decided to compile a new calendar. Guo Shoujing's mentor Zhang Wenqian oversaw the compilation of the new calendar, while Guo Shoujing's close friend Wang Xun was responsible for the specific testing and compilation. Recommended by his friend and mentor, Guo Shoujing, who had previously served in the water conservancy department, made a mid-career shift and began to devote himself to the great project of compiling the new calendar.
Guo Shoujing leveraged the exceptional hands-on skills he had cultivated since childhood to repair multiple surveying instruments and personally crafted nearly twenty types of more precise devices. The test results obtained using these instruments were far more reliable than those from earlier times. The reason the "Season-Granting Calendar" could come so close to the modern Gregorian calendar is inseparable from the precision instruments Guo Shoujing created. He once stated, "The foundation of a calendar lies in measurement, and for measurement, nothing is more important than instruments," a remark that has profoundly influenced later generations engaged in scientific research.
After four years of relentless effort, the "Season-Granting Calendar" was finally successfully compiled. Just at this moment, Wang Xun passed away due to illness, leaving the massive task of data organization entirely to Guo Shoujing. Over the next two years, Guo Shoujing devoted himself wholeheartedly to this work, ultimately completing the compilation of the "Season-Granting Calendar."
Guo Shoujing's outstanding contributions to the development of Chinese science and technology have long been remembered by later generations. In 1981, the International Astronomical Union named a crater on the moon "Guo Shoujing Crater" to commemorate the 750th anniversary of his birth.