Throughout human history, many devices have been invented to help people map, model, and track the changing patterns of the sky, ranging from sarson stones to the atomic clock. But in the Middle Ages, the most popular was the astrolabe—a mechanical device usually made from metal or wood that allowed a trained user to measure the position of the stars and planets and to calculate local time and geographical latitude. The astrolabe had been invented by the Greeks in either the second or third century b.c., and many different variations had been produced over the centuries by scholars in
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