Yi Xing

Yi Xing directed the development of the Da Yan (Great Expansion) calendar during the reign of Emperor Xuanzong of the Tang dynasty. The calendar incorporated improved astronomical observations and was considered one of the most accurate of its era in China.

Yes, Yi Xing was an ordained Buddhist monk as well as a mathematician, astronomer, and engineer who served the Tang court. He exemplified the integration of Buddhist scholarship with secular science in Tang China, and his religious vocation did not prevent his appointment to lead major imperial astronomical projects.

Yi Xing constructed an armillary sphere and related observational instruments to measure celestial coordinates and track the movements of the sun, moon, and stars. These instruments enabled the more precise observations that informed both his Da Yan calendar and his geodetic surveys.

Yi Xing supervised a large-scale survey that measured the length of a degree of meridian by observing the sun's shadow at multiple stations spread across the Tang empire. This was one of the earliest known efforts to determine the dimensions of the Earth through systematic field measurement.