Born in the first century AD in the city of Nanjing, Zhang Heng was an inventor, astronomer, mathematician, poet, and everything in between. He lived during the Eastern Han Dynasty, under the reigns of the Emperors Andi and Shundi. As an astronomer, Zhang Heng held an important post in court, maintaining the calendar, which in turn allowed the emperor to make accurate predictions about the cycles of the seasons and stars. While this might not be immediately apparent, Chinese subjects at that time believed that civil life was a reflection of heavenly life, and astronomers were instrumental in showing that these two worlds were in accord.
Zhang Heng came up with a detailed model of the earth and heavens, which he likened to an egg. The outer shell was the heavens, and the yolk at the center was the earth. While the overall idea here might have been incorrect in the eyes of present-day science, one must remember that Zhang Heng was writing nearly two thousand years before. Zhang Heng was able to demonstrate that the moon did not shine with its own light, and was able to explain lunar eclipses (again, valuable to show the heavenly knowledge of the imperial court). For more mundane matters (literally), Zhang Heng developed a working seismograph, one that used an ingenious technique to point out the direction of a quake’s epicenter.
Zhang Heng lived and worked between 78 CE to 139 CE, making him a contemporary of the thinkers and philosophers of the Roman Empire, especially Ptolemy, whose cosmological vision was quite similar to Zhang’s. Like those thinkers, his work laid the foundation for further technical and scientific achievements.