Aristarchus of Samos

Aristarchus of Samos was a visionary Greek astronomer and mathematician who, nearly two millennia before Copernicus, proposed that the Earth revolves around the Sun. Working in the intellectual tradition of Alexandria, he challenged the prevailing geocentric worldview with extraordinary boldness. His heliocentric hypothesis was reported by Archimedes and later by Plutarch, but it gained little traction in the ancient world. The idea was simply too radical — if the Earth moved, why could no stellar parallax be observed? The answer, that stars are incomprehensibly far away, was correct but unverifiable with ancient instruments. Aristarchus also developed a geometric method to estimate the relative distances and sizes of the Sun and Moon. While his measurements were imprecise by modern standards, the method itself was brilliantly conceived and represented a pioneering application of trigonometry to astronomy.

• First known heliocentric model — proposed Earth orbits the Sun • Geometric method to estimate Sun-Moon distance ratio • Estimated the relative sizes of the Sun, Moon, and Earth • Recognized that stars must be vastly distant to show no parallax