Designed by the Yuan Dynasty astronomer Guo Shoujing in 1276, this instrument was renovated and simplified on the basis of the structurally complex armillary spheres of the Tang and Song dynasties, hence it was called the “simplified armilla”. By separating the circles of the horizontal coordinate system from those of the equatorial system, it greatly reduced obscuration of the sky by the many rings of the old instruments. The instrument was composed of the mutually-independent equatorial mounting and horizontal mounting and graduated on the basis of 365.25 days, the length of time it takes for the earth to make one revolution around the sun. The equatorial mounting had four coordinates, centigrade markings and an equatorial circle, and was similar to the basic structure of the equatorial mounting of celestial chart type which is extensively used in modern telescope. The polar axis was propped up by two supports. Revolving around the polar circle were a pair of circles with a sighting tube. In order to reduce the friction between the centigrade markings and the equatorial circle, Guo Shoujing installed four small cylinders in between them. In terms of reducing frictional force, such structure was completely the same as the principle of contemporary “roller bearing”. The equatorial mounting of the simplified armilla was used for determining the equatorial coordinates, the longitudes and horizontal coordinates of the celestial bodies. Similar to contemporary altazimuth, the horizontal mounting of the simplified armilla was used for measuring the horizontal bearings and altitude of the celestial bodies. In the base of the simplified armilla was a square board which was used for bearing calibration. In the Ming Dynasty version of simplified armilla the square board was changed into a sundial.
The creation of the simplified armilla was a great leap forward in the Chinese history of astronomical instrument making. It was also a sophisticated technology in the world at that time. By contrast, it was not until more than 300 years later that similar instruments were invented in Europe.
The creation of the simplified armilla was a great leap forward in the Chinese history of astronomical instrument making. It was also a sophisticated technology in the world at that time. By contrast, it was not until more than 300 years later that similar instruments were invented in Europe.
