Site of the Zhou Gong Gnomon Observatory

Site of the Zhou Gong Gnomon Observatory

The Site of the Zhou Gong Gnomon Observatory is a cultural tourism attraction.

The Site of the Zhou Gong Gnomon Observatory is located about 1.5 kilometers north of Runan County. Also known as Tianzhong Mountain, it stands over ten feet tall and bears inscriptions reading "Zhou Gong Gnomon Observatory" and "The Most Central Place Under Heaven." Nearby stands a stele erected in the Xinsi year of the Daoguang reign during the Qing Dynasty, which was relocated to this site. It details the entire process of establishing the gnomon observatory.

The inscription reads: By order of King Cheng, the Duke (Zhou Gong) re-established the city of Luoyi, seeking the central point of the land and erecting numerous gnomons to measure the sun’s shadow. After three visits to the banks of the Ru River, he found only this spot where no shadow was cast. He then piled up earth and stones to mark the place, naming it Tianzhong Mountain. A gnomon was erected there to observe the sun’s shadow and measure the solar constants, using it as the reference point. Later, Zhou campaigned against the Huaiyi and attacked the Dongyi, bringing stability to the realm. At that time, the site was marked with an earthen gnomon, but over time it collapsed. To commemorate Zhou Gong’s measurement of the sun’s shadow, a stone gnomon was later carved and reinstalled here. The base of the platform is shaped like an inverted gate, standing six feet tall—it is called the “gnomon” (圭); atop it sits a square pillar of equal height—called the “style” (表). At the summer solstice noon, the shadow of the style does not extend beyond the upper edge of the gnomon, and no shadow falls on any side of the gnomon, hence it is also called the “Shadowless Platform.”