Zhang Pingzi

Zhang Heng
A stamp of Zhang Heng issued by China Post in 1955
Native name	張衡
Born	AD 78 Nanyang, China
Died	AD 139 (aged 60–61) Luoyang, China
Known for	Seismometer, hydraulic-powered armillary sphere, pi calculation, poetry, universe model, lunar eclipse and solar eclipse theory
Scientific career
Fields	Astronomy, mathematics, seismology, hydraulics, geography, ethnography, mechanical engineering, calendrical science, metaphysics, poetry

Zhang Heng
"Zhang Heng" in Traditional (top) and Simplified (bottom) Chinese characters
Traditional Chinese	張衡
Simplified Chinese	张衡
Transcriptions Standard Mandarin Hanyu Pinyin Zhāng Héng Gwoyeu Romatzyh Jang Herng Wade–Giles Chang1 Heng2 IPA [ʈʂáŋ xə̌ŋ] Wu Suzhounese Tsãn Ghén Yue: Cantonese Yale Romanization Chēung Hàhng IPA [tsœ́ːŋ hɐ̏ŋ] Jyutping Zoeng1 Hang4 Southern Min Hokkien POJ Tiong Hîng Middle Chinese Middle Chinese ʈjang hæng Old Chinese Baxter–Sagart (2014) *C.trang gˤrang

Zhang Heng (Chinese: ; AD 78–139), formerly romanized as Chang Heng, was a Han Chinese polymath from Nanyang who lived during the Han dynasty. Educated in the capital cities of Luoyang and Chang'an, he achieved success as an astronomer, mathematician, scientist, engineer, inventor, geographer, cartographer, artist, poet, statesman, and literary scholar.

Zhang Heng began his career as a minor civil servant in Nanyang. Eventually, he became Chief Astronomer, Prefect of the Majors for Official Carriages, and then Palace Attendant at the imperial court. His uncompromising stance on historical and calendrical issues led to his becoming a controversial figure, preventing him from rising to the status of Grand Historian. His political rivalry with the palace eunuchs during the reign of Emperor Shun (r. 125–144) led to his decision to retire from the central court to serve as an administrator of Hejian in Hebei. Zhang returned home to Nanyang for a short time, before being recalled to serve in the capital once more in 138. He died there a year later, in 139.

Zhang applied his extensive knowledge of mechanics and gears in several of his inventions. He invented the world's first water-powered armillary sphere to assist astronomical observation; improved the inflow water clock by adding another tank; and invented the world's first seismoscope, which discerned the cardinal direction of an earthquake 500 km (310 mi) away. He improved previous Chinese calculations for pi. In addition to documenting about 2,500 stars in his extensive star catalog, Zhang also posited theories about the Moon and its relationship to the Sun: specifically, he discussed the Moon's sphericity, its illumination by reflected sunlight on one side and the hidden nature of the other, and the nature of solar and lunar eclipses. His fu (rhapsody) and shi poetry were renowned in his time and studied and analyzed by later Chinese writers. Zhang received many posthumous honors for his scholarship and ingenuity; some modern scholars have compared his work in astronomy to that of the Greco-Roman Ptolemy (AD 86–161).