Zhao Youqin

Zhao Youqin

(born July 26, 1271, Poyang, China—died c. 1335, Longyou Mountains, Zhejiang province) Chinese astronomer, mathematician, and Daoist philosopher. He was one of the patriarchs of the northern branch of the Quanzhen (“Complete Perfection”) sect of Daoism. His astronomical treatise Gexiang xinshu (“New Writing on the Symbol of Alteration”) presents his cosmological theory featuring a flat Earth inside a spherical Heaven, his explanation of the lunar and solar eclipses, and his experiments with a camera obscura. The book also describes his methods of remote surveying with gnomons to measure the distance from the Earth to the Sun, the Moon, and the stars, as well as his procedure for calculating the value of π. His Xian Fo tongyuan (“On the Common Origins of [the Teachings of] Transcendentals and Buddhas”) is devoted to the “Inner Alchemy,” an esoteric discipline focusing on the attainment of immortality via respiratory and meditative practices.