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Hipparchus (Astronomer): Bc Hipparchus
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At the end of his career, Hipparchus wrote a book called Peri eniausíou megéthous ("On the Length of the Year") about his results. The established value for the tropical year, introduced by Callippus in or before 330 BC was 365 + 1/4 days. (Possibly from Babylonian sources, see above [???]. Speculating a Babylonian origin for the Callippic year is hard to defend, since Babylon did not observe solstices ... the only extant System B yearlength was based on Greek solstices. See below.) Hipparchus' equinox observations gave varying results, but he himself points out (quoted in Almagest III.1(H195)) that the observation errors by himself and his predecessors may have been as large as 1/4 day. He used old solstice observations, and determined a difference of about one day in about 300 years.
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In 514 BC Hipparchus was murdered by the Tyrannicides, Harmodius and Aristogeiton. This was apparently a personal dispute, according to Herodotus and Thucydides; Hipparchus had fallen in love with Harmodius, who was already the lover of Aristogeiton. When Harmodius rejected him, Hipparchus invited Harmodius\'s sister to participate in a religious festival only to spurn her when she appeared in her finest, insinuating that she was not a virgin. As a result, Harmodius and Aristogeiton assassinated him.
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Late in his career (possibly about 135 BC) Hipparchus compiled his star catalog, the original of which does not survive. He ... constructed a celestial globe depicting the constellations, based on his observations. His interest in the fixed stars may have been inspired by the observation of a supernova (according to Pliny), or by his discovery of precession (according to Ptolemy, who says that Hipparchus could not reconcile his data with earlier observations made by Timocharis and Aristillus; for more information see Discovery of precession).
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Bc Hipparchus