Aristarchus of Samos is an important ancient Greek astronomer. Aristarchus studied under Straton of Lampsacus, the successor of Theophrastos. Theophrastos succeeded Aristotle as head of the peripatetic school of philosophy, originally, in the Lyceum in Athens.
Aristarchus observed the summer solstice in 280 B.C., but other than that, we have no fixed dates for him. Estimates place his birth at around 310 and death about 30 years after the recorded solstice event. Aristarchus' significant claim to fame is as "the author of the heliocentric hypothesis," [Toomer]. This idea of Aristarchus, that the earth revolved around the sun was popularized by Copernicus about 1800 years later. Aristarchus also believed the earth rotated on its own axis. Although he was way ahead of his time on the relationship of earth to sun, Aristarchus also wrote from a geocentric basis. Unfortunately, his only extant writing is from this perspective.
The only surviving work by Aristarchus is On the Sizes and Distances of the Sun and Moon. Aristarchus' estimate is far off, but his method was good and it was the first known attempt at measurement using angular measurements.
Read more about Aristarchus in Discoveries in Science Made by Ancient Greek Scientists.
G. J. Toomer "Aristarchus" Who's Who in the Classical World. Ed. Simon Hornblower and Tony Spawforth. Oxford University Press, 2000.
"Aristarchus of Samos" A Dictionary of Scientists. Oxford University Press, 1999. Oxford Reference Online. Oxford University Press.
This is not the same man as the librarian and grammarian Aristarchus.