Zhao Youqin

Zhao Youqin (born July 26, 1271 in Poyang , † around 1335 in the mountains of Longyou ) was a Chinese astronomer , alchemist , Daoist and mathematician .

Zhao Youqin grew up during the time of the conquest of China by the Mongols ( Kublai Khan ) and was possibly involved in the fighting and wounded. He was a student of a Daoist, belonged to the northern school of Quanzhen Daoism and learned astronomy and alchemy in his youth. He became a hermit and wrote a commentary on the I Ching for ten years , but it has not survived. He was later ordained and patriarch of the Quanzhen School.

He wrote the book Ge xiang xin shu (New Scripture on the Symbol of Change), which contains astronomy, cosmology, calendar calculations and considerations on optics. The optical experiments on the apparent brightness were carried out with a camera obscura . According to him, the earth is flat and surrounded by spherical celestial balls. He also describes various astronomical instruments such as a gnomon with applications for measuring the distance from the earth to the sun, the moon and the stars, and tries to explain solar and lunar eclipses. Another astronomical instrument he described measured the angular distance of the celestial north pole to a star and another measured the right ascension between two objects in the sky. In particular, there is a method for calculating the number of circles . A polygon is iteratively inscribed on the circle, from a square and an octagon with doubling of the sides to a polygon with 16384 sides. Zhao Youqin thus received a value for pi of 3.141592. When calculating pi, it had a predecessor in China in Liu Hui (3rd century AD). ${\displaystyle \pi }$

Zhao Youqin's algorithm for calculating pi, shown is the second step in the transition from an inscribed square to an octagon

He also wrote a work on meditation ( inner alchemy ) and wisdom (Xian Fo tongyuan), which has also been preserved.

literature

• Alexei K. Volkov: Science and Daoism: an introduction, Special issue on science in 14th century China: a case study of Daoist master and polymath Zhao Youqin (1271-1335?), Taiwanese Journal for Philosophy and History of Science, Volume 5, 1997, pp. 1-58.
• AK Volkov: The mathematical work of Zhao Youqin: remote surveying and the computation of , Special issue on science in 14th century China: a case study of Daoist master and polymath Zhao Youqin (1271-1335?), Taiwanese Journal for Philosophy and History of Science, Vol. 5, 1997, pp. 129-189. ${\displaystyle \pi }$
• AK Volkov: Zhao Youqin and his calculation of , Historia Mathematica, Volume 24, 1997, pp. 301–331 ${\displaystyle \pi }$

Web links

• John J. O'Connor, Edmund F. Robertson :  Zhao Youqin. In: MacTutor History of Mathematics archive .
• Entry in the Encyclopedia Britannica