Hipparchus

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Hipparchus : biography

190 BC –

Geography

Hipparchus’ treatise “Against the Geography of Eratosthenes” in three books is not preserved.Editions of fragments: Berger H. . Leipzig: B. G. Teubner, 1869.; Dicks D.R. The Geographical Fragments of Hipparchus. London: Athlon Press, 1960. Most of our knowledge of it comes from Strabo. Hipparchus thoroughly and often unfairly criticized Eratosthenes mainly for internal contradictions and inaccuracy in determining positions of geographical localities. Hipparchus insists that a geographic map must be based only on astronomical measurements of latitudes and longitudes and triangulation for finding unknown distances. In geographic theory and methods Hipparchus introduced three main innovations.On Hipparchus’ geography see: Berger H. . Leipzig: B. G. Teubner, 1869.; Dicks D.R. The Geographical Fragments of Hipparchus. London: Athlon Press, 1960; Neugebauer O. A History of Ancient Mathematical Astronomy. Pt. 1-3. Berlin, Heidelberg, New York: Springer Verlag, 1975: 332–338; Shcheglov D.A. . Orbis Terrarum 9. 2003–2007: 159–192. He was the first to use the grade grid, to determine geographic latitude from star observations, and not only from the sun’s altitude, a method known long before him, and to suggest that geographic longitude could be determined by means of simultaneous observations of lunar eclipses in distant places. In the practical part of his work, the so-called “table of climata”, Hipparchus listed latitudes for several tens of localities. In particular, he improved Eratosthenes’ values for the latitudes of Athens, Sicily, and southern extremity of India.Shcheglov D.A. . Greek, Roman, and Byzantine Studies 45. 2005: 359–380; idem. “”. Klio 88. 2006: 351–359.; idem. . Orbis Terrarum 9. 2003–2007: 159–192. In calculating latitudes of climata (latitudes correlated with the length of the longest solstitial day), Hipparchus used an unexpectedly accurate value for the obliquity of the ecliptic, 23°40′ (the actual value in the second half of the 2nd century BC was approximately 23°43′), whereas all other ancient authors knew only a roughly rounded value 24°, and even Ptolemy used a less accurate value, 23°51′.Diller A. (1934). "Geographical Latitudes in Eratosthenes, Hipparchus and Posidonius". Klio 27.3: 258–269; cf. Shcheglov D.A. , 177–180. Hipparchus opposed the view generally accepted in the Hellenistic period that the Atlantic and Indian Oceans and the Caspian Sea are parts of a single ocean. At the same time he extends the limits of the oikoumene, i.e. the inhabited part of the land, up to the equator and the Arctic Circle.Shcheglov D.A. . Antike Naturwissenschaft und ihre Rezeption (AKAN) 17. 2007: 132-139. These Hipparchus’ ideas found their reflection in the Geography of Ptolemy. In essence, Ptolemy’s work is an extended attempt to realize Hipparchus’ vision of what geography ought to be.

Precession of the equinoxes (146–127 BC)

See also Precession (astronomy)

Hipparchus is known for being almost universally recognized as discoverer of the precession of the equinoxes in 127 BC.Giorgio de Santillana & Hertha von Dechend, "Hamlet’s Mill", David R Godine, Boston, publisher, 1977, p 66 His two books on precession, On the Displacement of the Solsticial and Equinoctial Points and On the Length of the Year, are both mentioned in the Almagest of Claudius Ptolemy. According to Ptolemy, Hipparchus measured the longitude of Spica and Regulus and other bright stars. Comparing his measurements with data from his predecessors, Timocharis and Aristillus, he concluded that Spica had moved 2° relative to the autumnal equinox. He also compared the lengths of the tropical year (the time it takes the Sun to return to an equinox) and the sidereal year (the time it takes the Sun to return to a fixed star), and found a slight discrepancy. Hipparchus concluded that the equinoxes were moving ("precessing") through the zodiac, and that the rate of precession was not less than 1° in a century.