Zhang Heng

From Freepedia

For other uses, see Zhang Heng (disambiguation).

Zhang Heng (張衡, Pinyin: Zhāng Héng, Wade-Giles: Chang Heng) (78 – 139) was an astronomer, mathematician, inventor, artist and literary scholar of the Eastern Han Dynasty in ancient China.

Born in what is now Nanyang, Henan, Zhang Heng was an accomplished writer at twelve. At sixteen, he left home to pursue his study in the capital cities. He spent at least ten years of his youth in literature studies and writing. He published several well recognized literary writings.

Zhang Heng began his studies in astronomy at thirty. He became a government official at thirty-eight. He took on several positions since then (mostly high-level academic posts). When he was a government minister, he cleaned up some corruption in the local government.

In 123, Zhang Heng corrected the Chinese calendar to bring it in line with the seasons.

In 132, Zhang Heng invented the first seismometer, called Houfeng Didong Yi (lit. instrument for measuring the seasonal winds and the movements of the Earth), for measuring earthquakes. On June 13, 2005, Chinese seismologists announced that they had created a replica of the instrument [1].

Zhang Heng theorized that the universe was like an egg with the stars on the shell and the Earth as the yolk. This was similar to the Western geocentric model before the coming of Galileo Galilei. He was the first person in China to construct a rotating celestial globe. He also invented the odometer.

In one of his publications, Ling Xian (靈憲, a summary of astronomical theories at the time), he approximated pi as 730/232 (or approx 3.1466). In one of his formulae for spherical volume calculation, he also used pi as the square root of 10 (or approx 3.162).

The lunar crater Chang Heng is named after him.