Heraklides of Pontus

Heraclides Ponticus (Ancient Greek: Ἡρακλείδης ὁ Ποντικός; c. 390 BC – c. 310 BC), also known as Herakleides and Heraklides of Pontus, was a Greek philosopher and astronomer who was born in Heraclea Pontica, now Karadeniz Ereğli, Turkey, and migrated to Athens. He is best remembered for proposing that the Earth rotates on its axis, from west to east, once every 24 hours. He is also frequently hailed as the originator of the heliocentric theory, although this is doubted.

Heraclides' father was Euthyphron, a wealthy nobleman who sent his son to study at the Platonic Academy in Athens under its founder Plato and under his successor Speusippus. According to the Suda, Plato, on his departure for Sicily in 361/360 BC, left the Academy in the charge of Heraclides. Heraclides was nearly elected successor to Speusippus as head of the academy in 339/338 BC, but narrowly lost to Xenocrates.

Like the Pythagoreans Hicetas and Ecphantus, Heraclides proposed that the apparent daily motion of the stars was created by the rotation of the Earth on its axis once a day. This view contradicted the accepted Aristotelian model of the universe, which said that the earth was fixed and that the stars and planets in their respective spheres might also be fixed. Simplicius says that Heraclides proposed that the irregular movements of the planets can be explained if the earth moves while the sun stays still.

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