In about 170 B.C., the Greek astronomer Hipparchus devised an instrument that could perform complex astronomical calculations, navigational computations, and even time measurements - a true analog computer. The user found the altitude of the sun or stars by means of a graduated circle on one side of the device; then turned to the other side to perform his calculations on the movable star map, a two-dimensional representation of the three-dimensional heavens.
Astrolabe
© 2000 The Computing History Museum, The American University, Washington D.C. 20016
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