The central axis of Beijing is actually crooked?

Science Times reporter epic

Recently, the "Magnificent Central Axis" World Cultural Heritage Beijing Central Axis Exhibition opened in Beijing. While enjoying the magnificent scenery, many citizens could not help but wonder: Is the Beijing Central Axis the exact dividing line of the city? Is it due south and due north?

The Central Axis of Beijing starts from Yongdingmen in the south, passes through Zhengyangmen, the Forbidden City, Jingshan, Drum Tower and Bell Tower in the north, and ends at the Bell and Drum Tower in the north. It is 7.8 kilometers long and is a combination of buildings and ruins that governs the entire planning pattern of the old city. It is also the central line of Beijing city.

"However, the central axis of Beijing is not the city's central dividing line. Strictly speaking, it is not due south or due north, but has a declination of two degrees from the meridian." Tian Lin, director of the Institute of Architecture and Public Art of the Chinese Academy of Arts, told the Popular Science Times reporter that why the central axis of Beijing deviates from the meridian is still a mystery. Some people speculate that one way to measure direction in ancient times was to use a magnetic needle, but the magnetic needle measured the direction of the earth's magnetism, which has a magnetic declination with the meridian. The magnetic declination of Beijing in the Yuan Dynasty was about two degrees, so the central axis was tilted.

Researchers from the Chinese Academy of Surveying and Mapping also selected three points on the Beijing topographic map: Yongdingmen, Di'anmen and Bell Tower, and calculated that the deflection angle was two degrees and a dozen minutes. To prove this phenomenon, researchers also conducted an "instant effect" test on the north-facing corridor under the Yongdingmen Tower, and the results also confirmed that the central axis of Beijing deviated from the meridian.