Born AD. 78; died AD. 139. Chinese astronomer.
Chang Heng was one of the first to explain the cause of lunar eclipses and the phenomenon of lunar phases. He correctly described the apparent motion of celestial bodies and designed and built several astronomical instruments. His book, The Armillary Sphere, which appeared circa 120, presented in detail the theory of the “infinite sky.” The theory holds that the universe is boundless in time and space.