Aristarchus (310 BC - c. 230 BC) was a Greek astronomer and mathematician, born on the island of Samos, in ancient Greece. He was the first Greek astronomer to propose a heliocentric model of the solar system, placing the Sun, not the Earth, at the center of the known universe (hence he is sometimes known as the "Greek Copernicus"). His astronomical ideas were not well-received and were displaced by those of Aristotle and Ptolemy, until they were successfully revived and developed by Copernicus nearly 2000 years later. The Aristarchus crater on the Moon was named in his honor.
Aristarchus believed the stars to be very far away, and saw this as the reason why there was no visible parallax, that is, an observed movement of the stars relative to each other as the Earth moved around the Sun.