As Grand Historian of the Latter Han dynasty, Zhang Heng was in charge of astronomic research, keeping the calendar, and monitoring the weather and earthquakes. He tracked the movements of Venus, Jupiter, Mercury, Mars, and Saturn for many years running, and accurately described their orbits.
東漢太史令張衡掌管天文曆法、氣象、地震測報，他長期觀測金木水火土五星運動，正確描述了行星軌道。