The Observatory at Dengfeng
Established by the Yuan astronomer Guo Shoujing (1231-1316), the observatory is the oldest of its kind in China. It has three parts: the body, the stone sundial and gnomon. The sundial is put flat on the platform pointing due north. At the north end of the sundial stands a stone gnomon.
The observatory dates back to 1276. Its functions were to help astronomers to measure the shade during the day, to observe Polaris at night; and to establish the exact time of sunrise and sunset. Based on the spot experiments, Guo Shoujing grasped the movement of the sun, the moon, the stars and the earth, determined the exact time of the twenty-four seasonal division points, such as the solstices and equinoxes. He calculated the length of a year at 365 days, 5 hours, 49 minutes and 20 seconds in his Shoushi Calendar, which was the most advanced in the world at that time.