Yi Xing

Yi Xing was a Chinese astronomer, Buddhist monk, inventor, mathematician, mechanical engineer, and philosopher during the Tang dynasty. His astronomical celestial globe featured a liquid-driven escapement, the first in a long tradition of Chinese astronomical clockworks. He was also a prominent figure in the history of Chinese Buddhism, being the seventh patriarch of the Huayan school and a disciple of the sixth patriarch Zhiyan. He was also involved in the translation and commentary of several Buddhist scriptures, and wrote treatises on topics such as meditation, logic, and cosmology. Yi Xing was born Zhang Sui in Nanle County, Henan, in 683. He showed an interest in astronomy and mathematics from an early age, and was also proficient in music and chess. He became a Buddhist monk at the age of 14, and took the monastic name Yi Xing, meaning "one practice". He studied under various masters of different Buddhist schools, and became well-versed in both the exoteric and esoteric teachings. He also traveled widely throughout China, visiting famous temples and monasteries, and engaging in debates and discussions with other monks and scholars. In 718, he was appointed by Emperor Xuanzong as the director of the Imperial Astronomical Bureau, and was tasked with reforming the calendar and conducting an astrogeodetic survey of the empire. He designed and built a water-powered armillary sphere and a celestial globe that could accurately display the movements of the sun, moon, and stars. He also devised a clepsydra clock that could measure time in units of one-sixtieth of a second. He used these instruments to observe and record various astronomical phenomena, such as eclipses, solstices, and equinoxes. He also calculated the length of the tropical year, the obliquity of the ecliptic, and the precession of the equinoxes, with remarkable precision. He also established 13 observation sites across the empire, and measured the latitudes and longitudes of these locations using the shadow lengths of the sun. He then used these data to determine the length of a degree of meridian, and the size and shape of the earth. He also corrected the errors and inconsistencies in the existing star maps and star catalogues, and compiled a new one based on his own observations. Yi Xing died on June 27, 727, at the age of 45, after a long illness. He was buried at Mount Tiantai, where he had spent his last years. He left behind a rich legacy of scientific and religious works, which influenced later generations of astronomers, mathematicians, engineers, and Buddhists. He was revered as a master of both the worldly and the transcendental, and was honored with various titles, such as "the sage of astronomy", "the master of Huayan", and "the great teacher of the three realms".