It is believed that the Duke of Zhou had erected at this place a Ceyingtai to observe the Sun. His interest in mathematics, astronomy/astrology is reported in the Zhoubi Suanjing.
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 deviations 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 this place is the center of the Earth.
Yuan Dynasty
The great observatory was built in 1276 in the early Yuan dynasty on the order ofKublai Khan and was used by Guo Shoujing and Wang Xun to observe the movement of the sun, the stars and record time. It was built of stones and bricks. It has two parts: the body and shigui. It is 9.46 meters high by itself, and 12.62 meters high if the 2 cabinets on the top are included. The somewhat unconventional gnomon is a bar mounted horizontally between the 2 cabinets. The shigui extending to the far north is 31.19 meters long and 0.53 meters wide. It is made up of 36 square stones with two parallel waterways on it to check its levelness. The location of shigui is in accordance with the direction we take today to measure the meridian. During measurement, a beam is put across the grooves. Jingfu on the waterways is used to measure the shade, whose precision is within 2 millimeters. At winter solstice, the length of the shadow at noon is nearly as long as the shigui. The very precise observations served for the new Shoushi calendar of 1281, which was in use for 364 years. The length of the tropical year was determined to 365 d 5 h 49 m 20 s, a value in accord with the value of the Gregorian Calendar, but obtained 300 years earlier. In 1787, Laplace applied these measurements to check his calculations on the secular changes of the obliquity of the ecliptic and the eccentricity of the Earth's orbit. It is the first in a series of 27 observatories built in the early Yuan dynasty.
Heritage status
As part of the "Dengfeng Historic Monuments of Dengfeng 'in the Center of Heaven and Earth'" the observatory has been listed as UNESCO World heritage in 2010.
