Anaxagoras realized that the moon was a rock, not a God, and the public banished him

(written by lawrence krubner, however indented passages are often quotes). You can contact lawrence at:, or follow me on Twitter.


Anaxagoras also wrestled with the origins and formation of the moon, a mystery that still challenges scientists today. The philosopher proposed that the moon was a big rock which the early Earth had flung into space. This concept anticipated a scenario for the moon’s origin that physicist George Darwin, son of Charles Darwin, would propose 23 centuries later. Known as the fission hypothesis, Darwin’s idea was that the moon began as a chunk of Earth and was hurled into space by the Earth’s rapid rotation, leaving behind the Pacific basin. (Today, many astronomers believe that a Mars-sized body slammed into the early Earth, expelling material that then coalesced into the moon, though other theories exist for the origin of our natural satellite.)

By describing the moon as a rock of terrestrial origin, and the sun as a burning rock, Anaxagoras moved beyond earlier thinkers, even those who realized the moon was a kind of reflector. This forward thinking got Anaxagoras labeled as a chief denier of the idea that the moon and sun were deities.

Such an idea should have been welcome in democratic Athens, but Anaxagoras was a teacher and friend of the influential statesman Pericles, and political factions would soon conspire against him. In power for over 30 years, Pericles would lead Athens into the Peloponnesian wars against Sparta. While the exact causes of these conflicts are a matter of debate, Pericles’ political opponents in the years leading to the wars blamed him for excessive aggression and arrogance. Unable to hurt the Athenian leader directly, Pericles’ enemies went after his friends. Anaxagoras was arrested, tried and sentenced to death, ostensibly for breaking impiety laws while promoting his ideas about the moon and sun.

“In the Athenian democracy, with its ‘democratic’ trials before large juries on criminal charges being brought by private citizens—there was no district attorney—all trials were basically political trials,” Graham says. “They were often disguised as being about religion or morality, but they aimed at embarrassing some public figure by going after him directly if he was vulnerable, or a member of his circle if he was not. If you wanted to attack Pericles, but he was too popular to attack directly, you found the weakest link in his group. As a foreigner and intellectual with unorthodox new ideas, Pericles’ friend and ‘science advisor’ Anaxagoras was an obvious target.”

Still holding some political sway, Pericles was able to free Anaxagoras and prevent his execution. Though his life was spared, the philosopher who questioned the divinity of the moon found himself in exile in Lampsacus at the edge of the Hellespont. But his ideas regarding eclipses and lunar phases would live on to this day, and for his recognition of the true nature of the moon, a lunar crater, visited by orbiting spacecraft some 2,400 years later, bears the name Anaxagoras.

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