Zhang Heng Armillary Sphere

A replica of Zhang Heng's water-powered armillary sphere on display in front of Taiwan's National Science and Technology Museum.

Armillary spheres consist of a framework of rings with three distinct layers and were used to aid in tracking the motion of the planets and stars. While most armillary sphere's are operated manually, Zhang's variation employed a waterwheel to power the sphere's mechanism and automate its motion, making one complete rotation each year.