Why is the central axis of the Forbidden City biased?

The central axis of Beijing is an extremely rare axis of architectural art in the history of world cities. However, after measurement, it is found that this line is not due south and north, but deviates from the meridian. If so, wouldn't the thrones of 33 emperors in Yuan, Ming and Qing Dynasties be crooked? Why does the central axis deviate from the meridian? Did the ancients do it on purpose? Or is there something wrong with the measurement? \ x0d \ x0d \ When it comes to Beijing's architectural planning, I'm afraid many people will think of the central axis, which is one of the most important architectural features. The central axis of Beijing starts from Yongdingmen in the south and passes through Zhengyangmen, Forbidden City, Jingshan, Bell Tower and Drum Tower in the north, with a total length of about 7.8 kilometers. Taking the Forbidden City as the center, it became the main line connecting the north and south cities at that time, and today, this central axis still plays a key role. This central axis is not a concrete "line", but relatively abstract, because there are some very unique architectural forms on it, so that we can see the traces in it, just like the beating music shown because of ups and downs. \ x0d \ x0d \ Many cities in China have a central axis, which often coincides with the meridian. Meridian is what we usually call the meridian connecting the north and south poles. A stone rat and a stone horse were dug up in a building in Beijing in the 1950s. These two isolated cultural relics are located in two different places on the central axis. In the ancient heavenly stems and earthly branches of China, the son was a mouse and the noon was a horse, suggesting that the central axis was actually the meridian of the city. \ x0d \ x0d \ Beijing is the imperial city, where 33 emperors of Yuan, Ming and Qing dynasties proclaimed themselves emperors. However, after a very careful study, an old gentleman found that the central axis and meridian were not exactly the same. From this point of view, it is possible that the thrones of 33 emperors are all inclined, and Beijing is not due south and north. So, does his theory make sense? Is that really the case? \ x0d \ x0d \ was surprised to find that \ x0d \ x0d \ Kui Zhongyu, a researcher at China Academy of Surveying and Mapping, has lived in Beijing for decades. Because I have been engaged in aerial remote sensing photography and mapping maps, I have a strong interest in ground objects. Once, he wanted to take a panoramic bird's eye view of Beijing. He first discovered an aerial photograph, which is a top view of the aerial photograph after processing and mosaic. In the face of high-definition images, Zhongyu Kun began to consider where to start shooting. At this time, he began to pay attention to the central axis of Beijing, which runs straight from north to south. Looking at it, he suddenly found that this line is not due south, but offset! \ x0d \ x0d \ Kui Zhongyu knows that the map is made under strict control of geographical coordinates, so there should be no problem. He immediately found the satellite image of Beijing. On the satellite map, the central axis also deviates from the meridian. He bought many versions of Beijing maps, including traffic and sightseeing maps of Beijing. At first glance, the results are a little biased, and the counterclockwise direction is a little biased. This proves that this line does have an angle with the meridian. \ x0d \ x0d \ deviating from the central axis is something worth pondering. When was the north-south central axis of Beijing formed and deviated? \ x0d \ x0d \ When the ancients built a city, they should establish a "central platform" as the geometric center of the city. From the Western Zhou Dynasty to the Liao and Jin Dynasties, the center and axis of the city kept drifting. It was not until the Mongolian fighters swept the square in the Yuan Dynasty that Beijing really became the political center of the country. \x0d\\x0d\ At that time, the center of the city was determined at the present location of the Drum Tower. After the center point is established, the central axis of the city and the position of the city are naturally established. Since then, the central axis has not changed for 800 years. Mr. Liang Sicheng once said, "Beijing's unique grand order is produced by the establishment of this central axis." The above facts show that the deviation of Beijing's central axis from the meridian was formed when the city was built in the Yuan Dynasty. In other words, the central axis deviated from the time when the Yuan Dynasty was established. \ x0d \ x0d \ Kui Zhongyu Considering that the central axis of Beijing has a certain deviation from the map, what is this angle? So Zhong-yu Kui decided to make a field survey of Yongdingmen. \x0d\\x0d\ Immediately measure the axis \x0d\\x0d\ To measure the meridian of Yongdingmen, it is very important to know the exact time when the sun passes through Yongdingmen. Together with experts, Zhong Yu Kui calculated the noon time when the sun passed through Yongdingmen according to the world time difference, local time difference, time difference of the day and other factors. \ x0d \ \ x0d \ 2004 day in the winter of 2004, Zhong-yu Kui and surveying and mapping experts started real-time testing on Yonglu Road facing north under Yongdingmen Gate Tower. They erected a 2-meter-long pole in the middle of Yonglu Road. Under the telephone pole, the center line of Yan Yong Road is northward, and a 6-meter-long black tape is attached to indicate the central axis. When the sun passes through the Yongdingmen meridian, the shadow of the pole is the Yongdingmen meridian. The angle between shadow and black tape is the angle between meridian and central axis. \ x0d \ x0d \ After accurate measurement and calculation, it is found that the central axis of Beijing deviates from the meridian by more than 2 degrees. Is this deflection angle calculated correctly? Kui Zhongyu also selected three points on the topographic map, namely Yongdingmen, Bell Tower and Di 'anmen, and calculated the deflection angle as 2 degrees and more than ten minutes, which proved that the real-time rough survey result of Yongdingmen was correct. According to this calculation, the central axis from Yongdingmen to the bell tower deviates from the meridian by 300 meters. \ x0d \ x0d \ is a calculation error \ x0d \ x0d \ but why is the central axis of Beijing biased? When the Yuan Dynasty Metropolis was built, was it deliberately biased, or was it caused by survey errors? \ x0d \ x0d \ The longitude, latitude and azimuth of all parts of the earth change with time. For example, there will be small periodic swings, movements and deflections during the earth's operation, which are called polar shift, nutation and precession in astronomy. So does the deviation of the central axis have anything to do with these astronomical phenomena? Kui Zhongyu specially consulted Mr. Xi, an academician of the Chinese Academy of Sciences. Xi is an astronomer and historian with an international reputation. After learning about the deviation of Beijing's central axis, he thought it inappropriate to link some astronomical phenomena with the deviation of Beijing's central axis. \ x0d \ x0d \ because the pole shift is a little movement in the earth's rotation, and the area is very small. Although precession and nutation will affect the latitude and longitude of the star position, they will not affect the latitude and longitude of the ground, so we can rule out the factors that the celestial phenomena affect the deviation of the central axis. \ x0d \ x0d \ So is it caused by a calculation error? In ancient China, accurate measurements were made very early. Scholars in the Tang Dynasty once measured the meridian accurately in Henan. We can clearly see the straight central axis of the city from the model of the imperial city in Song Dynasty restored by Henan archaeology. Astronomy, calendar, mathematics and other aspects in ancient China reached a fairly high level, so the deviation of the central axis should not be a measurement error. It's not a technical reason. What is it? \ x0d \ x0d \ What's in the distance? \x0d\\x0d\ In order to uncover the mystery hidden behind the central axis, Zhong Yu Kun temporarily abandoned the way of finding reasons based on natural and technical routes and began to look for humanistic clues. \ x0d \ x0d \ Kui Zhongyu, considering the trend of many ancient buildings, has a certain relationship with some distant features. Does the central axis of Beijing also have a certain relationship with distant buildings? Now Beijing was built on the basis of the Yuan Dynasty, which was built by Kublai Khan. Will Kublai Khan build buildings related to Beijing in other places before? \ x0d \ x0d \ Kui Zhongyu found several topographic maps from Beijing to Inner Mongolia. When he connected nine topographic maps, a place he had never paid attention to appeared. He was surprised to find that the central axis of Beijing extended northward, and its extension line pointed to Gukaiping, the birthplace of Kublai Khan in Yuan Shizu. \ x0d \ x0d \ 1206, Genghis Khan established the Mongol Empire. Twenty years later, Kublai Khan designed a city, built a palace and built Kaiping, the capital of the Yuan Dynasty, in Liu. \ x0d \ x0d \ Yuan Shangdu is closely related to Yuan Dadu. At that time, the Yuan Dynasty was dualistic, that is, a country had two capitals. So does this Beijing central axis have anything to do with yuan? There are always errors in the measurements on the map. In order to obtain more accurate results, it is necessary to use GPS global positioning system for more accurate mathematical calculation and field measurement. Kui Zhongyu decided to follow the central axis issued by Beijing and personally visit Inner Mongolia Autonomous Region. \x0d\\x0d\ Capital of searching for the past and exploring the present \x0d\\x0d\ The straight line distance from Beijing and Hebei to Zhenglan Banner in Inner Mongolia is 270 kilometers. Considering Quidditch, did the person in charge of the design at that time adopt the connection between the merchants and the metropolis as the baseline of the central axis of most cities according to the wishes of the rulers at that time, so as to reflect the unity of the two? With this question, accompanied by Sain, deputy director of the local cultural bureau, and Dong Xige, a historical researcher in Yuanshangdu, Kui Zhongyu went to the ruins in Yuanshangdu. The Yuanshangdu site is located in the northeast of Shangdu Town, Zhenglan Banner, Xilin Gol League, Inner Mongolia Autonomous Region. \ x0d \ x0d \ Yuanshangdu site has a history of hundreds of years. Kui Zhongyu walks in the ancient city of Shangdu. They are looking for a route extending from the ancient capital Beijing. They unfolded the map, looked for the central axis extending from Beijing in the ruins of Shangdu in Yuan Dynasty according to the GPS satellite locator, and matched it with the map. However, where is this invisible line? \x0d\\x0d\ [color=Red] When the GPS in Kui Zhongyu's hand shows east longitude 1 16 degrees 12, he knows that the point where the distance really passes through the central axis is only longitude 1 minute, which is a distance of several hundred meters. [/color] Zhong-yu Kui called this line connecting Yuandadu and Yuandu the "Two Beijing Lines". In this way, the central axis of Beijing is located at the southern end of the two capital lines. Scholars believe that modern people's accurate measurement methods should not be used to judge ancient people's measurement, because after all, at that time, they did not have such complete tools, and there is no need to accurately describe this central axis to four decimal places. \x0d\\x0d\ For Kui Zhongyu and many scientists, whether the reason for the deviation of the central axis is really determined by human factors remains to be further verified, but no matter what the answer is, many cultural relics and historical sites on the central axis that have gone through hundreds of years of wind, frost, rain and snow are destined to help people uncover this legendary mystery.