What is Zhang Heng?
{{no footnotes|date=February 2022}} {{Infobox scientist |name = Zhang Heng<br><small>{{lang|zh|張衡}}</small> |image = Zhang Heng.jpg |image_size = |caption = A stamp of Zhang Heng issued by [[China Post]] in 1955 |birth_date = AD 78 |birth_place = [[Nanyang, Henan|Nanyang]], [[China]] |death_date = AD {{death year and age|139|78}} |death_place = [[Luoyang]], China |field = [[Astronomy]], [[mathematics]], [[seismology]], [[hydraulics]], [[geography]], [[ethnography]], [[mechanical engineering]], [[Chinese calendar|calendrical science]], [[metaphysics]], [[poetry]] |known_for = [[Seismometer]], [[Hydraulics|hydraulic-powered]] [[armillary sphere]], [[pi|pi calculation]], [[shi (poetry)|poetry]], [[Shape of the Universe|universe model]], [[lunar eclipse]] and [[solar eclipse]] theory }} '''Zhang Heng''' (also written '''Chang Heng''', {{zh|t=張衡|s=张衡|p=Zhāng Héng}}; AD 78–139) was a [[China|Chinese]] [[scientist]] who worked in many subjects. He lived during the [[Han dynasty]]. He was an accomplished [[engineer]], [[meteorologist]], [[geologist]], [[philosopher]], [[mathematician]], [[astronomer]] and [[writer]]. Zhang invented the first [[seismometer]], a machine that measures the strength of earthquakes. He is remembered for many other inventions and writings. He invented the seismometer in 132 AD. Heng was also the first in China to apply a [[Grid reference|grid system]] to maps, from which positions and distances could be calculated. Some of his jobs were chief astronomer of the Imperial Chancellery for Astronomical and Calendrical Science, and chief minister under the rule of Moana. He also wrote many works ranging from poetry to books full of his scientific research. One was his book of astronomical research and it described his theories about previously unexplained things that could be seen in the night sky. Some things it theorized were that the [[Moon]] was lit by the [[Sun]] instead of making its own light. It also proposed that the Moon could be [[Lunar eclipse|eclipsed]] by the [[shadow]] of the Earth.