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Yi Xing

Type Figure Region China Time 683–727 Also known as Zhang Sui、Monk Yixing

Yi Xing (683–727) was a Tang astronomer, mathematician and Buddhist scholar, originally named Zhang Sui, who compiled the Dayan Calendar, first intro…

Timeline

  1. 683–700Changle, Weizhou · HebeiBorn Zhang Sui in Changle, Weizhou, he was precocious from childhood, well read in classics and history, skilled in calendrical calculation; fleeing Wu Sansi he hid in the mountains, later becoming a monk at Mount Song with the dharma name Yi Xing.
  2. 700–721Mount Song · HenanOrdained and practiced at Mount Song, studying under Hengjing of Jing Mountain and others, later learning Esoteric Buddhism from Vajrabodhi and Amoghavajra while also studying astronomy and calendrics, laying the foundation for his later calendar reform.
  3. 721–727Chang'an · ShaanxiOrdered by Emperor Xuanzong to lead a calendar reform, he compiled the Dayan Calendar with the innovative unequal-spacing quadratic-difference interpolation, organized meridian measurements at thirteen sites nationwide, and calculated one degree of meridian at about 351 li 300 bu, the world's first measurement of the earth's curvature; he died at Chang'an in 727.

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