Anaxagoras of Clazomenae was a Greek philosopher from Ionia who gave up his wealth to pursue a life of study. At the age of twenty, he moved to Athens and effectively established it as the new center of Greek philosophy. For three decades he helped shape the thoughts of a number of illustrious pupils, including Pericles the statesman, Euripides the playwright, and possibly even Socrates.

Anaxagoras's explanations of the Moon's light, eclipses, earthquakes, meteors, rainbows, sound, and wind seem surprisingly modern, and he put forward some provocative ideas that bore on the possibility of extraterrestrial life. He thought, for instance, that the Moon has "a surface in some places lofty, in others hollow" and that a race of humans dwelt there. He also postulated that the Sun was a brightly glowing rock "bigger than the Peloponnese" and that the stars were other suns lying at such a distance that they appeared to give out no heat. When he was about 33, a meteorite big enough to fill a wagon landed in broad daylight near the town of Aegispotami. Anaxagoras caused a sensation by claiming it had come from the Sun. To him, there was no difficulty in thinking about the Sun and Moon as sizable, physical objects rather than as deities. In fact, in place of the traditional pantheon of gods, he argued that there was just a single eternal intelligence, or "Nous", which pervades the cosmos. The Athenian authorities, smarting from a recent military defeat at the hands of the Persians, were in no mood to be subverted from within by such heretical views and arrested Anaxagoras. Charged with impiety, he was sentenced to death. Fortunately Pericles, the most respected man in Athens, put in a good word for him and the sentence was commuted to exile. Anaxagoras retired to Lampsacus on the Dardanelles where he continued teaching for another twenty years.