The enactment of taichu calendar law. In BC 104, the Western Han Dynasty began to enact the taichu calendar Law. In the process of making taichu calendar, the Gaitian School, represented by Sima Qian, had a heated debate with the emerging Huntian School. Finally, the important figure of Huntian School is Luo, who "adjusted Huntian to the ground for Emperor Xiao of Han Dynasty and made taichu calendar regularly." [[ 13]] "Turn to the sky" can be understood as measuring the sky with an armillary sphere or demonstrating the sky with an armillary sphere. We tend to understand it as measuring the sky with an armillary sphere, because measurement was a big problem in the mud cover dispute at that time. At the beginning of the debate, Sima Qian's practice of "fixing things, building coffins, missing engravings, and parting with twenty-eight lodgings" [14]] was measurement. The survey method of Gaitian [[ 15]], that is, "the table stands in the middle of the north and south, the rope is tied to the top, and the spokes lead the rope as the hub", has inherent requirements for the position of the surveyor, and the survey without the ground is theoretically untenable. [[ 16]] The ancients had a deep understanding of this. In the Tang Dynasty, Li pointed out in the Biography of Liu Xiang Hong Fan in the Western Han Dynasty that "the shadow of Xia is one foot, five inches and eight minutes": "It is Chang 'an, the capital of Han Dynasty, but it is not a place for surveying shadows. If you are in Chang' an, it is not a positive shadow. " ([7]) Huntianjia went to Yangcheng in the middle of the earth, far away from Chang 'an, the capital of the Western Han Dynasty, which not only reflected the authority of the obtained data, but also explained the theoretical defects of Gaitianjia's measurement method. Perhaps it was the measurement made by Luoxiahong on the land thousands of miles away from Chang 'an that led to the taichu calendar plan put forward by Huntianjia gaining the upper hand in the mud cover dispute. To take a step back, even if the "turning to the sky" of the sunset is to demonstrate the sky by turning to the sky, he is also doing it all the way to the ground. Here, the concept of "middle place" played an important role in the formulation of "taichu calendar" and the mud-covered dispute that began for hundreds of years, and the Dengfeng stargazing platform, as the embodiment of the concept of "middle place", was related to this historical event.

Astronomical geodesy in kaiyuan period of tang dynasty. In the 9th year of Kaiyuan (AD 72 1), the monks and their party were ordered to draw up Great Yan Li. To make the Dayan calendar, we must first carry out astronomical geodesy. According to "New Tang Book Tian", "He and his party wrote" Da ",saying that the Grand Master measured the coffins of the world and asked for its soil, thinking that it was a destiny." In the soil or in the ground, which shows that this kind of measurement is linked with the concept of the ground from the beginning. This investigation was undertaken by Nangong in the Kaiyuan period, starting from 72 1 and ending in 725. In order to carry out this investigation, the expedition team members set up nine observation stations, including Yangcheng, from Lin Yi (near Hue in central Vietnam) at 0/7.4 N to Yuzhou (near Lingqiu in northern Shaanxi) at 40 N. Along this meridian, which is 7973 miles (more than 3500 kilometers) long, the traditional eight-foot meter is used to measure the shadow length of the second solstice in winter and summer, and to measure the height of the North Pole. Before the specific investigation began, in order to highlight the status of Yangcheng and commemorate the traditional theory of local middle schools, Nangong said that the Duke of Zhou observation deck was established by imperial decree in Yangcheng. The specific process has been discussed in the previous chapter. Nangong said that this measurement is the first time to measure the meridian length of 1 in the world, and the measurement results played an important role in the formulation of Dayan calendar. Dr. Needham commented, "This is the most noteworthy organized field survey conducted in the early Middle Ages in the world." [[ 17]] Yangcheng is an important observation point in this survey, and the Zhougong observation point built in Yangcheng is the physical witness of the ancient land view, and it is also a landmark monument of the astronomical geodetic historical events organized by a group of people such as Nangong. After the investigation, when compiling Dayan Calendar, a group of people compared the data obtained by photogrammetry in Yangcheng with the data of other measuring points for many times, which highlighted the importance of photogrammetry in Yangcheng.

After the Tang Dynasty, the ancients in China also made many systematic star observations. During the more than one hundred years in the Northern Song Dynasty, five systematic star observations were made, all of which took the Duke of Zhou Observatory as an important observation point. Especially in the calendar reform in the early Yuan Dynasty, in order to provide accurate astronomical data for making calendars, Guo Shoujing led a large-scale "Four Seas Examination". The observation range starts from the South China Sea at 15 north latitude, and a point is set every 10 until the place at 65 north latitude. Twenty-seven observation stations and observation stations have been established, covering a wide range and large scale. The observatory was built for this observation and is the central observation station of this activity. According to the records left at that time, among the 27 observation points, only Dadu (now Beijing) and Yangcheng (now Dengfeng was successful, that is, the location of Dengfeng Stargazing Observatory) were used for photogrammetry, and only Yangcheng built a high platform for photogrammetry, leaving only Dengfeng Stargazing Observatory. When Guo Shoujing organized this survey, Dengfeng was neither a political center, an economic center, nor a cultural center. In this case, Guo Shoujing chose to build a surveying platform in Dengfeng, naturally because Dengfeng is the traditional position in the land, and the results obtained here are more authoritative and comparable. The Dengfeng Stargazing Observatory established by Guo Shoujing has survived to this day, which is worthy of being the physical witness of astronomical geodesy organized by Guo Shoujing in the early Yuan Dynasty.

After the founding of People's Republic of China (PRC), the observation platform and related cultural relics were strengthened and maintained. 196 1 year, the State Council designated Dengfeng stargazing platform as a national key cultural relics protection unit.