Zhang Heng

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Zhāng Héng

Replica of Zhang Heng's seismometer Houfeng Didong Yi

For other uses, see Zhang Heng (disambiguation).

This is a Chinese name; the family name is Zhang

Zhang Heng (張衡, Pinyin: Zhāng Héng, Wade-Giles: Chang Heng) (78 – 139) was an astronomer, mathematician, inventor, artist, poet 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.

Xiao Tong (501-531) immortalized several of Zhang's works in his anthology of literature, Wen xuan. Rhapsodies (fu 賦) include "Western Metropolis Rhapsody" 西京賦 (WX 2.36), "Eastern Metropolis Rhapsody" 東京賦 (WX 3.51), "Southern Capital Rhapsody" 南都賦 (WX 4.68), "Rhapsody on Contemplating the Mystery" 思玄賦 (WX 15.213), and "Rhapsody on Returning to the Fields" 歸田賦 (WX 15.222). The latter fu is an especially interesting piece, being very short compared to his other, mainly long epedeictic fu, and possessing a lyrical quality and refinement beyond its time. A set of four short lyric poems shi 詩, entitled "Lyric Poems on Four Sorrows" 四愁詩, is also included with Zhang's preface (WX 29.414). This set constitutes some of the earliest heptasyllabic shi Chinese poetry written.

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. Zhang Heng is also the first known Chinese to have invented the armillary sphere. He catalogued 2500 stars alone and recognize over 100 constellations, more than Hipparchus' 800 stars.

In 123, Zhang Heng corrected the Chinese calendar to harmonize 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).