Aristillus was a Greek astronomer

Astronomy

Astronomy is a natural science that deals with the study of celestial objects and phenomena that originate outside the atmosphere of Earth...

, presumably of the school of Timocharis

Timocharis

Timocharis of Alexandria was a Greek astronomer and philosopher. Likely born in Alexandria, he was a contemporary of Euclid....

 (c.300 BC). He was among the earliest meridian-astronomy observers.
Six of his stellar declinations are preserved at Almajest 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(2007).

Aristyllos 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 [1982] 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

Aristillus (crater)

Aristillus is a prominent lunar impact crater that lies in the eastern Mare Imbrium. Directly to the south is the smaller crater Autolycus, while to the southwest is the large Archimedes. The area of mare to the southwest is named the Sinus Lunicus...

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