Greek astronomer and mathematician (c.310–c.230 BC)
Aristarchus of Samos (c. 310 – c. 230 BC) was an ancient Greek astronomer and mathematician who devised the first known model envisioning the Earth in motion, orbiting around the Sun, or "central fire," at the center of the universe. He was influenced by Philolaus, and argued, like Anaxagoras before him, that the stars were entities similar to the sun. His astronomical ideas were in large rejected in favor the prevailing geocentric models of Aristotle and Ptolemy, until De revolutionibus orbium coelestium was published in 1543 by Copernicus, who was influenced by the work of Aristarchus through a close reading of Greek and Latin authors. The only known extant work by Aristarchus is "On the Dimensions and Distances of the Sun and Moon" which does not discuss his thesis on heliocentrism.
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Proposition 1. Two equal spheres are comprehended by one and the same cylinder, and two unequal spheres by one and the same cone which has its vertex in the direction of the lesser sphere; and the straight line drawn through the centres of the spheres is at right angles to each of the circles in which the surface of the cylinder, or of the cone, touches the spheres.
We are now in a position to prove the following propositions : —
1. The distance of the sun from the earth is greater than eighteen times, but less than twenty times, the distance of the moon (from the earth); this follows from the hypothesis about the halved moon.
2. The diameter of the sun has the same ratio (as aforesaid) to the diameter of the moon.
3. The diameter of the sun has to the diameter of the earth a ratio greater than that which 19 has to 3, but less than that which 43 has to 6; this follows from the ratio thus discovered between the distances, the hypothesis about the shadow, and the hypothesis that the moon subtends one fifteenth part of a sign of the zodiac.
[Hypotheses]
1. That the Moon receives its light from the sun.
2. That the earth is in the relation of a point and centre to the sphere in which the moon moves.
3. That, when the moon appears to us halved, the great circle which divides the dark and the bright portions of the moon is in the direction of our eye.
4. That, when the moon appears to us halved, its distance from the sun is then less than a quadrant by one-thirtieth of a quadrant.
5. That the breadth of the (earth's) shadow is (that) of two moons.
6. That the moon subtends one fifteenth part of a sign of the zodiac.