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Seng Yixing
Tang monk and astronomer, born Zhang Sui, who drafted the Dayan calendar for Emperor Xuanzong and organized empire-wide shadow and pole-height measurements
On an observatory terrace at night, a large bronze armillary sphere stands on a stone base while two people stand with their backs turned facing the view; stars are joined into constellation lines overhead, and a sundial and tiered dripping water vessels stand at the right.
Also known as Zhang Sui · Dahui Chanshi
Yixing, born Zhang Sui in Changle in Weizhou, was a grandson of the early Tang minister Zhang Gongjin and became a Buddhist monk after a youth spent reading the classics. In 717 Emperor Xuanzong had a kinsman carry an edict to Jingzhou summoning him to the capital, and in 721, after the Linde calendar had repeatedly mispredicted eclipses, ordered him to draw up a new one. He had Liang Lingzan carve a wooden model of an ecliptic armillary, later cast in bronze, and the two also built a water-driven celestial globe whose wooden figures beat a drum and struck a bell at set hours. For the calendar he organized shadow and pole-height observations across the empire; Nangong Yue's team in Henan found that the pole's altitude changed by one degree over 351 li 80 bu. Yixing died in 727, aged forty-five by Chinese count, with the title Chan Master Dahui, and the Dayan calendar that Zhang Yue and Chen Xuanjing compiled from his drafts was issued in 729.
Life and times
Dates 683 CE–727 CE