Aristyllus

Aristyllus (; fl. c. 261 BC) was a Greek astronomer, presumably of the school of Timocharis (c. 300 BC). He was among the earliest meridian-astronomy observers. Six of his stellar declinations are preserved in the Almagest (7.3). All are exactly correct within his over-cautious rounding to 1/4 degree. See discussion (and lessons) at DIO 7.1 ‡1 p. 13.

Aristyllus was long mis-dated to c. 300 BC (which made his data look among the poorest of the ancients); but when his correct date was found by least-squares (Isis 73:259-265 p. 263), it was realized that his star declinations' accuracy was unexcelled in antiquity. His data suggest that he worked in Alexandria: see DIO 4.1 ‡3 Table 3 p. 45 (2004).

A lunar crater, Aristillus, aptly near the Moon's meridian and at a lunar latitude roughly equal to the terrestrial latitude of Alexandria, is named after him.