Tang Dynasty
The astronomer Yi Xing of the Tang Dynasty built 20 standardized gnomons spread out over China to measure the equation of time dependent on the geographical location. Following a proposition of Liu Zhuo from 604 AD, 10 of these were aligned along the meridian 114° east of Greenwich from Central Asia down to Vietnam in order to determine the circumference of the Earth and derivations from a perfect sphere. One of these 10 observatories was situated at Gaocheng. The observations were used to establish the Da Yan calendar.
South of the observatory, in the temple dedicated to Zhou Gong can be found a Shigui chart made by Yi Xing. According to the Zhou Li (Rites of Zhou) this place is the center of the Earth.
Read more about this topic: Gaocheng Astronomical Observatory
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