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History

The astrolabe is an analog computer used to calculate the position of the sun and stars. For fifteen centuries it was the ultimate astronomical instrument. The astrolabe was probably invented by the Greeks in the early years of the first millennium. Ptolemy (2nd century AD) refers to the mathematics used to construct the astrolabe, and Theon of Alexandria (4th century AD) wrote the first treatise on this versatile instrument. In the middle ages, Arabic astronomers preserved and added to the knowledge of the Greeks. By the eleventh century, astrolabes were known in Europe through trade with the Arabs. The astrolabe was used chiefly for telling time and in calculations pertaining to astrology. The oldest surviving English-language treatise on the astrolabe was written by none other than Canterbury Tales author Geoffrey Chaucer. Careful inspection of his fictional work reveals numerous references to astrolabes and other astronomical phenomena.