Who postulated a heliocentric theory in the 3rd century B.C.E.?

The heliocentric theory, which posits that the Sun is at the center of the universe and that the Earth and other planets revolve around it, was notably suggested by Aristarchus of Samos in the 3rd century B.C.E. This revolutionary idea contrasted sharply with the prevailing geocentric view, which placed the Earth at the center of the universe. Aristarchus is often celebrated for his foresight and for laying the groundwork for later astronomers, including Copernicus, who is more widely known for advancing the heliocentric model in the 16th century.

Eratosthenes is best known for his work in geography and for calculating the Earth's circumference, while Hipparchus made significant contributions in the fields of astronomy and mathematics but did not propose a heliocentric model. Thales is one of the earliest pre-Socratic philosophers and is more associated with early cosmological ideas rather than with the development of heliocentric theory. Thus, Aristarchus stands out as the key figure in proposing the heliocentric view during that time.