The observatory tower
Of stone and brick.
Windmemories — CC BY-SA 4.0 · 白诗棋 — CC0 · Gary Todd from Xinzheng, China — CC0 · xiquinhosilva — CC BY 2.0 · Gary Todd from Xinzheng, China — CC0 · Siyuwj — CC BY-SA 4.0 · Gary Todd from Xinzheng, China — CC0 · Gary Todd from Xinzheng, China — CC0
One of the oldest surviving astronomical observatories in China, built in 1276 at the start of the Yuan dynasty on the order of Kublai Khan and designed by the astronomers Guo Shoujing and Wang Xun to track the sun and stars and keep time, on a spot where astronomers had measured the sun's shadow for centuries: the Duke of Zhou is said to have set up a gnomon here around 1042 BC, believing the place the centre of heaven and earth. The tower, of stone and brick, is 9.46 metres tall, or 12.62 metres with the two rooms on top, between which a horizontal bar casts its shadow on the «sky-measuring ruler», a stone channel running 31.19 metres north and 0.53 metres wide, made of 36 square stones with two parallel water channels to check that it is level; south of the observatory stands a Tang-era stone gnomon attributed to the astronomer Yi Xing, and in 2010 the observatory was inscribed on the World Heritage List among the Dengfeng monuments. Entry is free and the site is open from 8 am to 5 pm, per the Dengfeng city government and visitor guides.
Of stone and brick.
31 metres long.
South of the observatory.
Gaocheng Town, south-east of Dengfeng
A horizontal bar between the tower's two rooms cast its shadow on a long stone channel called the «sky-measuring ruler», and astronomers measured the noon shadow through the year to set the calendar.