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Hipparchus (c.190-c.120 BC), Ancient Greek astronomer, at the Alexandria Observatory, Egypt. At left is the armillary sphere he invented. Hipparchus is considered one of the greatest astronomers of antiquity. He calculated the length of the year and discovered the precession of the equinoxes. It is thought that the later work of Ptolemy was based on the work done by Hipparchus. Engraving from Vies des Savants Illustres (1877).
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