Development of Ancient Astronomy:The Peak of Yuan Dynasty Astronomy

The development of astronomy cannot be separated from the construction of astronomical observatories. In the Yuan Dynasty, many astronomical observatories were built in Shangdu, Dadu and Dengfeng. Yuan Dynasty eight years, Yuan Shizu Kublai in Shangdu presided over the construction of Shangdu Observatory, appointed the Arab astronomer Zamarudin is responsible for the specific work, the observatory is located in the north gate of Shangdu which is an ancient city. Shangdu Observatory east-west length of 132 meters, north-south width of 52 meters, about 12 meters high. Its plane is concave. Its two sides are integrated with the city wall, which is part of the whole city wall, but higher than the city wall, and the back wall protrudes from the city wall by about 1 m each.The seven pieces of astronomical instruments made by Zamaruddin placed in the Observatory have obvious Western characteristics, which are different from the traditional Chinese astronomical instruments. In the ninth year of the Yuan Dynasty, Shizu decided to move the capital to Dadu. After his arrival in Dadu, he collected many astronomical talents. In the 16th year of the Yuan Dynasty, he authorized the construction of the Metropolis Observatory, which was located under the eastern city wall and was in charge of the Taishi Hall. The platform was 7 feet high and divided into 3 levels. The courtyard wall was about 123 meters long and 92 meters wide. Most observatories had astronomical observatories on the upper level, library materials, star charts, muddy images, time-keeping funnels, and indoor instruments on the middle level, and offices for Tai Shi Yuan on the lower level. The Metropolitan Observatory is a very large observatory with a large staff, well-designed and well-equipped. Dengfeng Observatory, located in Gaocheng Town, Dengfeng County, Henan Province, was built in the early Yuan Dynasty. It is the earliest surviving ancient astronomical observatory building in China and one of the important astronomical monuments in the world. The structure of the Observatory is divided into two parts: one part is the towering platform surrounded by the island ladder, and the other part is the gui laid flat to the north in the groove of the north wall of the platform. The platform is barrel-shaped, 9.46 meters high, and 12.62 meters high even in a small room. The top surface of the platform is square, with each side more than 8 meters long and the bottom side more than 16 meters long. The groove in the middle of the Taipei wall was the standard for measuring the sun's shadow. Exquisite astronomical instruments Guo Shoujing, an outstanding astronomer of the Yuan Dynasty, once proposed that the calendar is based on the koan, and the koan's instrument is not an instrument first. In other words, the premise of astronomical observation is to create advanced astronomical instruments. Therefore, Guo Shoujing created as many as 13 kinds of observational instruments, including equipment for celestial azimuth measurements, sun and shadow measurements, time measurements, celestial demonstrations, etc., as well as portable instruments for easy field observations. Famous instruments include the Simple Instrument, the Elevated Instrument, and the Sundial Table. The Simple Instrument is a simplification and improvement of the previous armillary sphere. It is an astronomical instrument that simulates the celestial sphere and measures the five elements of sun, moon, gold, wood, water, fire and earth and their positions. It is very similar to the British device used in modern telescopes. The improved simplex instrument is much more accurate. The simple instrument is a treasure in Chinese astronomy, which is three to four hundred years earlier than similar instruments in the world; and the ball-bearing device used in the simple instrument is 400 years earlier than the ball-bearing device invented in the West. To date, there are still copies of the Jan Yee from the Ming Dynasty. Yang Yi is an astronomical instrument created in the Yuan Dynasty to measure the position of the sun, the direction of solar eclipse, deficit and time. It is a hollow spherical instrument made of copper, with the four directions of southeast, northwest, and twelve o'clock engraved on the hemisphere, as well as the equatorial coordinates corresponding to the latitude of the earth being observed. The sun through the hemisphere has a hole in the flat plate in the coordinates projected an inverted image, you can read the position of the earth in the sky. It was the world's first solar projector. It is a completely innovative astronomical instrument that changes the upward view to a downward view, reducing the pain of direct sunlight and making it less fatiguing. The homing table consists of two parts: the homing table and the homing table.

Guo Shoujing led an unprecedented latitudinal survey, from the Korean Peninsula in the east, to the Sichuan-Yunnan and Hexi Corridor in the west, to the vicinity of Chamchung in the south, and to the poor Tiele in the north, and successively set up 27 heliophotographic stations for observation. History books call it the Four Seas Test. Because this observation network was distributed in large cities all over the world, with observation points set up at 10-degree intervals from 15 to 65 degrees north latitude, it yielded highly accurate data. Compared with modern latitude values, the average error is mostly within half a degree. The angle between the plane of the ecliptic and the plane of the equator, known today as the angle of intersection between the plane of the ecliptic and the plane of the equator, is one of the most basic data in astronomy and is used in many calendar calculations. Measurements before the Yuan Dynasty were not very accurate, and the angle of intersection of the ecliptic and equator was long thought to be 24 degrees. The new astronomical instrument in Guo Shoujing was used to re-measure the angle of intersection of the yellow and red, and the data of the angle of intersection of the yellow and red was 23 degrees and 90 minutes, which was converted into the present 23 degrees and 33 minutes and 53 seconds, and differed from the modern observation value by only 1 minute and 6.8 seconds. This was undoubtedly the most accurate in the world at that time. The twenty-eight stars were the basis for measuring the positions of the stars in ancient China. At that time, people divided the stars near the ecliptic into twenty-eight nights, with one star representing one night. The distance between two stars was called the distance. Yuan had measured the distance five times before, but the error was still large. After Guo Shoujing's precision measurements, the accuracy was greatly improved, with a total absolute error of 2 degrees and 10 minutes, and an average error of only 4 minutes and 5 seconds, nearly doubling the accuracy of the data measured by Chongning in the Northern Song Dynasty. Guo Shoujing also observed more than 1,000 new stars that had never been named before, bringing the number of observable stars in the Yuan Dynasty to nearly 2,500. In pre-Renaissance Europe, only 1,022 stars could be measured. This is the best evidence that astronomy reached its zenith in the Yuan dynasty. In fact, astronomy in the Yuan Dynasty was developed in the process of compiling the new calendar, the Gregorian calendar. After the unification of the whole country, Kublai established the Bureau of Taishi in the first month of the thirteenth year of the Yuan Dynasty, taking the compilation of the calendar as an important initiative for the unification of the dynasty. The Bureau of Imperial History was headed by Wang Bi, the ruler of Zanshan and the son of a drinking nation. Wang Gao put Xu Heng, a former left minister who had returned home sick, on the job, and Guo Shoujing was appointed to assist. In the compilation of the calendar, Xu Heng was responsible for theoretical guidance, while the practical work was undertaken by Wang Bi and Guo Shoujing respectively. Other participants were Japanese officials Chen, Mao, Liu Juyuan, and Wang Su. After four years of hard work, by the winter solstice of the seventeenth year of the Yuan Dynasty, the new calendar was completed, and Kublai named it the Calendar of the Granted Time, meaning respect for the people. The compilation of the calendar was a major breakthrough in ancient astronomy in China. In Guo Shoujing's own words, it means seven things for the examiner and five things for the creator, i.e., seven astronomical data were verified and five new data were calculated. Seven astronomical data: First, thirteen to seventeen years to the winter solstice; second is the position of the sun at the time of the winter solstice; third, the moment when the moon passes the perigee; fourth is the length of the return year and the age difference constant, 365.2425 days a year; is the fifth winter solstice before the moon rises above the intersection of the moment; is the equatorial coordinates of the twenty-eight constellations; is the seven yuan of the time of the sunrise, sunset and the length of day and night. Five new data: the daily rate of the Sun's orbit on the ecliptic, the daily rate of the Moon's orbit around the Earth, the longitude of the equator calculated from the Sun's ecliptic longitude, the latitude of the equator calculated from the Sun's ecliptic longitude, and the intersection of lunar eclipses with the equator.