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The greatest of the Greek astronomers. Hipparchus compiled an extensive star  catalogue in which
stars were classified in "magnitudes" according to their brightness. Hipparchus found the
distance to the Moon using parallax, and, independently of Kiddinu of Babylon, discovered
precession of the equinoxes  by comparing his observations with those Timocharis 150 years earlier
(Dreyer 1953, p. 203; Heath 1981, p. 172; Sarton 1964, p. 44; Sarton 1965, pp. 43 and 299). Hipparchus extended
Apollonius of Perga's work on epicycles and eccentrics by offsetting the Earth from the center of the
planets' orbits in order to explain the different lengths of the
seasons. Hipparchus's model was a mathematical, not mechanical model, and it provided a
simpler explanation of stations and retrogressions that did Eudoxus's hippopede.
 Apollonius, Eudoxus, Kiddinu, Timocharis
Additional biographies: Greek and Roman Science and Technology, MacTutor (St. Andrews)
Dreyer, J. L. E. A History of Astronomy from Thales to Kepler, 2nd ed. New York: Dover, p. 203, 1953.
Heath, T. L. Aristarchus of Samos: The Ancient Copernicus. New York: Dover, p. 172, 1981.
Sarton, G. A History of Science, Vol. 1: Ancient Sciences through the Golden Age of Greece.
New York: Wiley, p. 444, 1964.
Sarton, G. A History of Science, Vol. 2: Hellenistic Science and Culture in the Last Three Centuries B.C.
New York: Wiley, pp. 53 and 299, 1965.
© 1996-2007 Eric W. Weisstein
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