Why does the central axis of the Forbidden City deviate?
Beijing’s central axis is an extremely rare axis of architectural art in the history of world cities. However, after measurement, it was found that this line was not due south or north, but deviated from the meridian. If this is the case, wouldn't the thrones of the 33 emperors of the Yuan, Ming and Qing dynasties all be crooked? Why does the central axis deviate from the meridian? Was it intentional by the ancients? Or is there something wrong with the measurement?
When it comes to Beijing’s architectural planning, many people will probably think of the central axis, one of the most important architectural features. The central axis of Beijing starts from Yongding Gate in the south and passes through Zhengyang Gate, Forbidden City, Jingshan, Bell Tower and Drum Tower in the north, with a total length of approximately 7.8 kilometers. With the Forbidden City as the center, it became the main line connecting the north and south cities at that time. Today, this central axis still plays the role of the backbone. This central axis is not a specific "line", but is relatively abstract. Because there are some very unique architectural forms on it, we can see the traces, just like the pulsing waves shown due to the ups and downs. movement.
Many cities in our country have central axes, and they are often consistent with the meridian. The meridian is what we usually call the longitude connecting the north and south poles. During a construction project in Beijing in the 1950s, a stone rat and a stone horse were excavated. These two isolated cultural relics were located at two different places on the central axis. Among the ancient Chinese heavenly stems and earthly branches, the child is the rat and the noon is the horse, implying that the central axis is actually the meridian of the city.
Beijing is an imperial capital, where 33 emperors from the Yuan, Ming and Qing dynasties proclaimed themselves emperors. However, an old gentleman discovered after very careful study that the central axis and the meridian were not exactly consistent. Looking at it this way, it is possible that the thrones of the 33 emperors are all crooked, and the city of Beijing is not facing south or north. So, does his theory make sense? Is this really the case?
Surprising discovery
Kui Zhongyu, a researcher at the China Academy of Surveying and Mapping, has lived in Beijing for decades. Since he has been engaged in aerial remote sensing photography and surveying and mapping work, he has a deep understanding of the ground. Have a strong interest in physical objects. Once, he wanted to take a panoramic aerial view of Beijing. He first found an aerial image. An aerial image is a top view of aerial photography photos that have been processed and mounted. Faced with high-definition images, Kui Zhongyu began to wonder where to start shooting. At this time, he began to pay attention to the central axis running directly from north to south in Beijing. As he looked at it, he suddenly discovered that this line was not due south or north, but was offset!
Kui Zhongyu knew that the map was strictly controlled according to geographical coordinates, so there should be no problem . He immediately found satellite images of Beijing. In the satellite image map, the central axis also deviated from the meridian. He also bought many versions of Beijing city maps, including Beijing traffic and sightseeing maps. At first glance, it turned out that they were all a little bit off, and a little bit counterclockwise. This proves that this line does have an angle with the meridian.
The deviation of the central axis is something worth pondering. When was the north-south central axis of Beijing formed, and when did it deviate?
When ancient people built a city, they would build a "central platform" as the geometric center of the city. From the Western Zhou Dynasty to the Liao and Jin Dynasties, the center point and central axis of the city continued to drift. It was not until the Yuan Dynasty that the Mongolian cavalry swept through all directions, and Beijing truly became the political center of the country.
At that time, the center point of the city was determined at the current location of the Drum Tower. After the center point was established, the central axis of the city and the location of the city were naturally established. In the 800 years since then, the central axis has remained unchanged. Mr. Liang Sicheng once said, "Beijing's unique and magnificent order was created 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 Yuan Dynasty was built. This means that the central axis has been skewed since the construction of Yuandadu.
Kui Zhongyu considered, since it was found on the map that Beijing's central axis deviates to a certain extent, how big is this angle? So Kui Zhongyu decided to conduct an on-site measurement of Yongding Gate.
Measuring the axis immediately
To determine the meridian of Yongding Gate, you must first know the precise time when the sun passes through the top of Yongding Gate. This time is very critical for measurement. Kui Zhongyu and experts worked together to determine the noon time when the sun passes through Yongding Gate based on calculations based on various factors such as world time zones, local time differences, and daily time differences.
One day in the winter of 2004, Kui Zhongyu and surveying and mapping experts began an immediate test on the Yong Road heading north under the Yongding Gate Tower. They erected a 2-meter-long pole in the middle of the corridor. Under the pole, extending the center line of Yong Road to the north, a 6-meter-long black tape is glued to represent the central axis. When the sun passes through the mid-heaven above Yongding Gate, the shadow of the pole is the Yongding Gate meridian. The angle between the shadow and the black tape is the angle between the meridian and the central axis.
After precise measurements and calculations, it was found that Beijing’s central axis deviated from the meridian by more than 2 degrees. Is the calculation of this declination angle correct? Kui Zhongyu also selected three points on the topographic map: Yongding Gate, Bell Tower and Di'an Gate, and calculated that the declination angle was 2 degrees and a dozen minutes, which proved that the rough measurement results of Yongding Gate's immediate effect were correct. According to this calculation, from The central axis from the beginning of Yongding Gate has already deviated from the meridian by 300 meters when it reaches the bell tower.
Is it a calculation error?
But why is the central axis of the capital skewed? When Yuan Dadu was built, was it deliberately biased, or was it caused by measurement errors?
The longitude, latitude, and azimuth angles of various places on the earth will undergo certain changes with time. For example, small periodic swings, movements, deflections, etc. will occur during the movement of the earth. , which is called polar shift, nutation and precession in astronomy, so whether the deviation of the central axis is related to these astronomical phenomena, Kui Zhongyu specifically consulted Xi Zezong, an academician of the Chinese Academy of Sciences. Xi Zezong is an internationally renowned astronomer and astronomical historian. After learning about the deviation of Beijing's central axis, he thought it was inappropriate to link some astronomical phenomena with the deviation of Beijing's central axis.
Because the polar shift is a little movement inside the earth during the earth's rotation, the area is very small. Although precession and nutation will affect the changes in the longitude and latitude of the star positions, they will not affect the changes in the longitude and latitude of the ground. Therefore, the factors that astronomical phenomena affect the central axis deviation can be eliminated.
So is it caused by calculation errors? my country has had precise measurements very early in ancient times. Scholars from the Tang Dynasty once measured the meridian very accurately in Henan. The straight central axis of the city can be clearly seen from the model of the Song Dynasty imperial city restored through archeology in Henan. In ancient my country, we have reached a very high level in astronomy, calendar, mathematics and other aspects, so the deviation of the central axis should not be a measurement error. If it’s not a technical reason, then what is it?
What is the distance?
In order to uncover the mystery hidden behind the central axis, Kui Zhongyu temporarily put aside the search for causes based on natural and technological routes and began to look for humanistic clues.
Kui Zhongyu considered that the direction of many buildings in ancient times had a certain relationship with some distant features. Does the central axis of Beijing also have a certain relationship with distant local buildings? The current city of Beijing was built on the basis of Yuan Dadu, and Yuan Dadu was established by Kublai Khan of the Yuan Dynasty. Did Kublai Khan build any buildings related to Beijing in other places before?
Kui Zhongyu found several topographic maps from Beijing to Inner Mongolia. When he connected the nine topographic maps and looked at them, a place he had never paid attention to appeared in front of him. He was surprised to find that the central axis of Beijing extended to the north, and its extension line pointed directly to ancient Kaiping, which was the birthplace of Kublai Khan, the founder of the Yuan Dynasty.
In 1206, Genghis Khan founded the Mongol Empire. More than twenty years later, Kublai Khan designed the city, built palaces and palaces within the territory, and built Kaiping, the capital of the Yuan Dynasty.
Both Yuan Dynasty and Yuan Dynasty have a very close relationship. At that time, the Yuan Dynasty was a two-capital system, that is, one country had two capitals. So, is the central axis of Beijing related to Yuan Dynasty? , there are always errors in measurements on maps. To obtain more accurate results, more precise mathematical calculations and on-site measurements using the GPS global satellite positioning system are needed. Kui Zhongyu decided to follow the central axis issued by Beijing and go to the Inner Mongolia Autonomous Region to inspect it personally.
Exploring ancient times and exploring present-day Shangdu
The straight-line distance from Beijing and Hebei to Zhenglan Banner in Inner Mongolia is 270 kilometers. Kui Zhongyu considered whether the person responsible for the design at that time would In accordance with the wishes of the rulers at that time, in order to reflect the unification of the two capitals, the line connecting Xanadu and Dadu was used as the baseline of the central axis of Dadu? With this question in mind, Kui Zhongyu, accompanied by Sai Yin, deputy director of the local cultural bureau, and Dong Xige, a researcher on the history of Shangdu in the Yuan Dynasty, set out for the ruins of Shangdu in the Yuan Dynasty. The Yuan Shangdu ruins are located in the northeast of Shangdu Town, Zhenglan Banner, Xilingol League, Inner Mongolia Autonomous Region.
After hundreds of years of changes, the ruins of Yuan Shangdu have long since become ruins. Kui Zhongyu was walking in the ancient city of Shangdu. They were looking for the line extending from the ancient capital Beijing. They unfolded the map and used the GPS satellite locator to find the central axis extending from Beijing in the Shangdu ruins of the Yuan Dynasty, and compared it with the map one by one. Confrontation, but where is this invisible line?
[color=Red] When the GPS device in Kui Zhongyu’s hand showed 116 degrees and 12 minutes of east longitude, he knew that there was only 1 minute of longitude away from the point that actually passed through the central axis, that is, how many degrees A distance of 100 meters. [/color]Kui Zhongyu called the line connecting Yuan Dadu and Yuan Shangdu the Liangdu Line. Looking at it this way, the central axis of Beijing City is located at the southern end of the Liangdu Line. Scholars believe that we should not use the precise measurement methods of modern people to judge the measurements of ancient people, because after all, at that time, they did not have such complete tools, and there was no need to depict this central axis to 4 decimal places. after.
For Kui Zhongyu and many scientists, whether the cause of the deviation of the central axis is really determined by human factors remains to be further verified, but no matter what the answer is, those on the central axis have experienced several The many cultural and historical relics of hundreds of years of wind, frost, rain and snow are destined to help people uncover this legendary mystery.