(fl. ca. 270 B.C.)
We may infer when Aristyllus flourished from the information provided by Ptolemy and from the date of Hipparchus’ observations.
He is mentioned by Plutarch in De Pythiae oraculis (402 F)-with Aristarchus, Timocharis, and Hipparchus-as an astronomer who wrote in prose. His name also occurs in two catalogs of commentators on Aratus; although two persons named Aristyllus are mentioned, the reference may be to one and the same person, as Maass maintains. Aristyllus’ name also occurs in a catalog of astronomers who wrote about “the pole,” i.e., about the polar stars. More important is the information we find in Ptolemy’s Syntaxis mathematica. He mentions Aristyllus and Timocharis as two astronomers whose observations of the fixed stars (declinations and differences of longitude) were used by Hipparchus. The latter, partly because of the differences between his own observations and those made a hundred years earlier by Aristyllus and Timocharis, discovered the precession of the equinoxes and calculated the amount of retrogression of the equinoctial points. According to Ptolemy, the observations of Aristyllus were not very accurate.
Aristyllus’ observations are recorded in Ptolemy, Syntaxis mathematica, Heiberg ed., VII, 1 and 3. See also “Aristyllos,” in Pauly-Wissowa, Real-Encyclopädie der Altertumswissenschaft, II, 1 (Stuttgart, 1895), cols. 1065–1066; and E. Maass, Aratea (Berlin, 1892), pp. 121, 123, 151.