Purple Mountain Observatory, built in China marked the beginning of modern astronomical research, China's many branches of modern astronomy observatory stations and mostly born from here, the formation and expansion. Since its establishment and made ​​a special contribution to the development of astronomy career in China, known as the "cradle of Chinese modern astronomy." 

Armillary sphere is observing the ancient Chinese instrument used to measure the coordinates of celestial sphere, which is composed of a heavy concentric rings, the whole thing looks like a ball. Data show that in the middle of the 4th century BC, the Chinese had been using astronomical observations of the armillary sphere, than about ancient Greece as early as 60 years. The most basic component armillary sphere is four meter swim and equatorial ring. In ancient times, "muddy" word contains the meaning of sphere. The ancients believed that the sky is round, shaped like a shell, the stars appear in the sky is embedded in the shell of the projectile, the Earth is the yolk, one to measure the position of the moon and stars on the yolk. Thus, the instrument of this observation positions of celestial bodies called "armillary sphere."