Aristarchus of Samos (c. 320–c. 250 BC)

Greek astronomer. The first to argue that the Earth moves around the Sun, he was ridiculed for his beliefs. He was also the first astronomer to estimate (quite inaccurately) the sizes of the Sun and Moon and their distances from the Earth.

Aristarchus was born on Samos and may have studied in Alexandria, where he died. His only surviving work is Magnitudes and Distances of the Sun and Moon. He produced methods for finding the relative distances of the Sun and Moon that were geometrically correct but rendered useless by inaccuracies in observation.

Aristarchus' model of the universe described the Sun and the fixed stars as stationary in the cosmos, and the planets – including the Earth – as travelling in circular orbits around the Sun. He stated that the apparent daily rotation of the sphere of stars is due to the Earth's rotation on its axis as it travels along its orbit, and that the reason no stellar parallax (change in position of the stars) was observed from one extreme of the orbit to the other is that even the diameter of the Earth's orbit is insignificant in relation to the vast dimensions of the universe.