Gaocheng Astronomical Observatory 观星台

About Gaocheng Astronomical Observatory

Its Yuan-period platform supported a horizontal bar whose shadow fell along a long stone measuring scale extending northward. Water channels helped establish a level reference. The instrument sits within a place associated with earlier observations and the Duke of Zhou, so the visit links a long intellectual tradition with a particularly concrete surviving device for observing the sun.

According to local tradition, the Duke of Zhou erected a shadow-measuring observatory (Ceyingtai) at the site to observe the sun, believing the area to be the center of heaven and earth. In the Tang dynasty the astronomer Yi Xing (683-727) built twenty standardized gnomons across China to measure the equation of time by location, ten of them aligned along a meridian running from Central Asia to Vietnam to determine the earth's circumference; an observatory at Gaocheng was one of these ten, and its observations helped establish the Dayan calendar.

The present Yuan-dynasty structure, of stone and brick, is 9.46 meters high on its own and 12.62 meters high including its two cabinets; the shigui, a stone scale extending north, is 31.19 meters long and 0.53 meters wide, made of 36 square stones with two parallel waterways to check its level. An instrument called jingfu was used to read the shadow's position to within 2 millimeters. Observations made here underpinned the Shoushi calendar of 1281, which remained in use for 364 years and fixed the length of the tropical year at 365 days, 5 hours, 49 minutes and 20 seconds, a value close to that of the later Gregorian calendar.

What to look for

• The raised observatory platform and the horizontal-bar arrangement above it.
• The long northward stone scale and its levelling channels, which explain how shadows were measured.

The surrounding area

Provincial capital base for Henan Museum and regional transfers; urban sightseeing is distinct from Dengfeng.

Location & getting there

Getting to Gaocheng Astronomical Observatory

Travel to the observatory in Gaocheng Town, southeast of central Dengfeng. Ask for Dengfeng Guanxingtai at the Duke of Zhou shrine; it is a separate road journey from the Shaolin and Songyang Academy areas.