There are many historical clues sprinkled around China testifying to an advanced knowledge of astronomy, one of the most visible being the Purple Mountain Observatory. Situated at 267m above sea level, it is located on the third peak of Zĭjīnshān Mountain (紫金山) in Nanjing. While the institution opened in 1928, PMO was given its present name in 1934. Its relics include the 60-cm-caliber reflecting telescope, 20-cm-caliber refracting telescope and meridian transit. There are also many instruments from ancient times, including the armillary sphere, abridged “armilla” and gnomon:

Armillary Sphere

Zhang Heng designed the armillary sphere during the Eastern Han Dynasty (25-220). Astronomers used its three nested rings to calculate the positions of the stars. The sphere is also a piece of art, with dragons intertwined on four poles and nature designs carved at the base. Although German troops moved the sphere to Berlin in the 1900s, they returned it to China in 1920.

Abridged Armilla

Guo Shoujing simplified the armillary sphere during the Yuan Dynasty (1271-1368). His version lets the rings approximate the equatorial ecliptic and horizontal coordinates of celestial bodies separately from one another. He also included a sun dial. Although the Allies looted the area in 1900, the abridged armilla returned to PMO in 1905.

Gnomon

The gnomon is one of China’s earliest inventions, dating back 3,000 years to the Yin-Zhou dynasties. A horizontal slab of rock casted a shadow on its horizontal counterpart, measuring solstices and hours.

All of these instruments led to the discovery of the 365.25-day solar year by the Chinese.