Chapter 38 218 Guo Shoujing revised the calendar

Before Yuan Shizu Kublai Khan came to the throne, he paid attention to absorbing scholars of the Han nationality to help plan major political affairs.He reused Liu Bingzhong, a Han counselor.It was Liu Bingzhong's idea that Kublai Khan proclaimed himself emperor and named the country Yuan.Later, Liu Bingzhong recommended some friends and students to Kublai Khan, and each of them served as important officials in the early years of the Yuan Dynasty.One of them was Guo Shoujing, a famous scientist in the Yuan Dynasty. Guo Shoujing is a native of Xingzhou (now Xingtai, Hebei).His grandfather, Guo Rong, was very knowledgeable, not only proficient in classics, but also studied mathematics, astronomy, and water conservancy.When Guo Shoujing was young, under the influence of his grandfather, he became very interested in science.At that time, Liu Bingzhong and his friend Zhang Wenqian were giving lectures at Zijin Mountain in the southwest of Xingzhou. Guo Rong sent his grandson to study with Liu Bingzhong.Guo Shoujing met many science-loving friends there, and his knowledge grew faster.

After Kublai Khan unified the north, in order to develop agricultural production, he decided to improve water conservancy and recruit talents in this area.Zhang Wenqian recommended Guo Shoujing to Kublai Khan, and Kublai Khan soon summoned Guo Shoujing in Kaiping (now east of Zhenglan Banner, Inner Mongolia).Guo Shoujing was very familiar with the water conservancy situation in the north, and proposed six measures for water conservancy improvement at that time.Kublai Khan was very satisfied after listening to it, and nodded his approval after listening to each item.Finally, he said with emotion: "If such a person is allowed to do things, he won't just put on airs and eat." After the interview, he sent Guo Shoujing to take up the post of promoting various rivers and canals to handle the water conservancy of the rivers.

Two years later, Guo Shoujing was sent to the Xixia area to improve water conservancy.After years of war there, the river course was silted up, the land was barren, and the production was severely damaged.When Guo Shoujing arrived in Xixia, after a detailed survey, he mobilized migrant workers to dredge a number of existing channels and dams, and also dug some new river channels.In less than a year, more than 9 million mu of farmland in this area has been irrigated smoothly, the grain harvest has been bumper, and the lives of the people have also improved. In order to strengthen the transportation from Dadu to the south of the Yangtze River, Kublai Khan sent Guo Shoujing to survey the waterway traffic situation.After Guo Shoujing's survey and design, not only the original canal was repaired, but also a new Tonghui River was dug from Dadu to Tongzhou. In this way, the water transportation from Jiangnan to Dadu will be unimpeded.

After Yuan Shizu destroyed the Southern Song Dynasty, he paid more attention to the recovery of agricultural production.Agricultural production should use the calendar.In the past, Mongolia has always used the calendar promulgated by the Jin Dynasty. This calendar has a large error, and even the solar terms often used in agriculture are not accurate.After the Yuan Dynasty conquered Jiangnan, another calendar was used in the south. The northern and southern calendars were different, which was more likely to cause confusion.Yuan Shizu decided to unify and formulate a new calendar.He ordered the establishment of an institution for compiling the calendar, called Taishi Bureau (later called Taishiyuan).Guo Shoujing's classmate Wang Xun was in charge of the Taishi Bureau.Because of his proficiency in astronomy and calendar, Guo Shoujing was also transferred from the water conservancy department to the Taishi Bureau by the imperial court, and together with Wang Xun, he presided over the work of changing the calendar.

At the beginning of the revision of the calendar, Guo Shoujing pointed out that to study the calendar, we must first pay attention to observation, and observation must rely on instruments. It turned out that there was a large armillary sphere transported from Kaifeng to observe the sky, which was so old that reliable data could not be obtained.Guo Shoujing designed a new set of instruments.He felt that the original armillary sphere was complicated in structure and inconvenient to use, so he created a simple instrument with a relatively simple structure and precise scale.The instruments he made are much more refined and accurate than the old ones.With good instruments, accurate field observations are also required.In 1279 AD, when Guo Shoujing reported to Emperor Shizu of the Yuan Dynasty, he proposed to build a new Sitiantai in the Taishi Academy and at the same time carry out large-scale astronomical surveys across the country.This bold plan was immediately approved by Yuan Shizu.

After research by Wang Xun, Guo Shoujing and others, 27 measuring points were set up all over the country.The northernmost measuring point is Tiele (in the Yenisei River Basin in present-day Siberia), and the southernmost measuring point is in the South China Sea (on the present-day Xisha Islands). Fourteen monitoring officials were selected to conduct observations in various places.Guo Shoujing also personally took people to several important observation points to observe.Observation points in various places aggregate all the data obtained to the Taishi Bureau.Based on a large amount of data, Guo Shoujing spent two years compiling a new calendar called "Shoushi Calendar".This new calendar is much more accurate than the old one.It calculates that there are 365.2425 days in a year, which is only 26 seconds different from the time for the earth to revolve around the sun.This calendar has the same one-year cycle as the current Gregorian calendar (that is, the Gregorian calendar).However, Guo Shoujing's "Shoushi Calendar" was 302 years earlier than the Europeans established the Gregorian calendar.