At the end of the sixth year of the Ming Dynasty (462 AD, the third year of the Northern Wei Dynasty), a manuscript on the discussion of the calendar was placed in front of Liu Jun, and the person who wrote the book was none other than the famous great scientist Zu Chongzhi.
Zu Chongzhi (祖冲之), also spelled Wenyuan, was born in fanyang ancestral clan, and his ancestral home was Fanyang County. Seeing this, is there anyone who will ask, also from the Fanyang Zu clan, Zu Chongzhi should not be a relative of Zu Ti, right? In fact, although the two are the same sect, there is no direct blood relationship, Zu Chongzhi's great-grandfather Zu Taizhi is Zu Ti's brother of the same clan, so the relationship between Zu Chongzhi and Zu Ti is that Zu Shang was once a person, nothing more.
Because his grandfather Zu Chang was a master of the Liu Song Dynasty, that is, an official in charge of civil engineering in the imperial court, and his father Zu Shuozhi was also knowledgeable, Zu Chongzhi was able to receive a good family education from an early age. In this environment, Zu Chongzhi was familiar with the scriptures and classics from an early age, and he had a strong interest in astronomy and mathematics. Gradually, Zu Chongzhi became a polymath and became famous.
Zu Chongzhi's reputation soon reached Liu Jun's ears, and Liu Jun sent Zu Chongzhi to hualin Xue Province, the academic research institution of the Liu Song court at that time, to do research work, and then transferred to the post of General Mingguan. This place is undoubtedly a good place for Zu Chongzhi, who is also here and has come into contact with a large number of national books, including books on astronomy, calendar, and arithmetic, which has allowed him to absorb a lot of knowledge. In the fifth year of the Ming Dynasty (461 AD, the second year of The Peace of Northern Wei), Zu Chongzhi was transferred to the post of official in Southern Xuzhou and joined the army in the gongfu.
Returning to the beginning of the article, Zu Chongzhi told Liu Jun above that there were problems and omissions in the "Yuan Jia Calendar" compiled by He Chengtian, which is now used, and Zu Chongzhi compiled a "Great Ming Calendar" (also called "Jiazi Yuan Calendar") for this purpose. ), and presented it to Liu Jun. The "Yuanjia Calendar" mainly corrects the location of the winter solstice time and winter solstice day set by the old calendar, changes the "Pingshuo" to "Dingshuo", creates the method of adjusting the day, reforms the "Shangyuan Accumulation Year Method", calculates the precession value of one hundred years, simply put, it is to set 7 leap months for 19 years, 1 solar year is about 365.2467 days, and one synodic month is about 29.530585 days. The Yuan Jia Calendar can be said to be a major progress in the history of Chinese calendar law at that time.
But Zu Chongzhi felt that the calendar used now fixed the solar terms of the winter solstice on a certain day, so that every less than a hundred years would be two degrees different. The new calendar to be formulated now is to put the winter solstice at the end of the year, with only a small gap in each year, and it will be used for a long time in the future, so there is no need to change it many times. In addition, the current calendar uses "son" as the beginning of the "chen", located just north. The 'void' is also arranged among the northern constellations. The calendar to be formulated is to put the upper yuan at the end of the year, starting from the virtual. In addition, the current calendar is to put the signs of the sun, moon and stars at the front with the nails as the beginning. The new calendar is to put the upper yuan on the nails every year. In addition, He Chengtian's calendar is that the sun, moon, and five stars each have their own yuan. The new calendar is to meet the sun, the moon, the five stars, and the speed of operation, all starting from the beginning of the year of the yuan.
I believe that basically most people do not know what is said above, to put it simply, that is, the length of the synodic month used in Zu Chongzhi's calendar is 29.5309 days, which is less than a second away from the length of the synodic moon measured by modern astronomical means. Proposed in 391 inserts 144 leap months of leap weeks. The length of the return year of the "Great Ming Calendar" is 365.24281481 days, which is only about six days away from the length of the return year measured in modern times, and the difference is only more than 50 seconds a year, which shows its accuracy. Since the winter solstice point is the starting point for the formulation of the calendar, determining its position in the sky is very important for the calendar.
When Liu Jun saw such a recital, he probably saw it in the clouds and fog, and he could not decide it himself, so he ordered those who had studied the calendar to debate with Zu Chongzhi, but he could not refute Zu Chongzhi. However, Dai Faxing and others resolutely suppressed and resisted this, and other things happened later, so Zu Chongzhi's new calendar was not implemented in the Liu Song Dynasty.