Soon after Anaxagoras had published his theory of the heavens, a shooting star appeared in the daytime, leaving a trail as it plunged through earth’s atmosphere. It crashed to the ground in the vicinity of Aegospotami “Goat Rivers,” a town in the Hellespont in northern Greece. It left a large stone the size of a wagon, presumably in a huge crater.[1] It would become a tourist attraction down to the time of the Roman Empire. It was, in modern terms, a meteorite from outer space.
Something strange happened in the report of the falling star. Instead of being reported as a missile thrown by Zeus, as would have happened in previous ages,[2] it was hailed as proof that Anaxagoras the natural philosopher was right in his cosmological account of the heavens. For, unlike virtually all of his predecessors, who had maintained that the heavenly bodies were made of air or fire, something as light as or lighter than air, Anaxagoras had claimed that there were stony and earthy bodies circling the earth.
Given that a large boulder had fallen out of the sky, and that this was a natural, not supernatural, event, it must follow that there are rocks in the sky. The story circulated that Anaxagoras had “predicted” the fall of a heavenly stone. Now of course one could not predict the fall of a meteor in the sense of identifying a date and time for a meteor strike. But in a weak sense, Anaxagoras had, it seemed, warned that one of the stones circling the earth, if it collided with another stone or the like, could fall to earth.[3] And no other theorist had conceived of such a possibility. So the falling star had Anaxagoras’ reception as a wise man with outstanding scientific insight.
We do not know all the details of Anaxagoras’ astronomy, but it seems likely that he described the moon as being earthy at least in part because, given Parmenides’ account of the moon as reflecting the sun’s light, it followed that it was a dark, opaque body. If the sun’s light could penetrate it, the moon would appear as a faintly glowing disk even when we beheld its “dark” side. But in fact, it becomes invisible from earth during the new moon, when we it shows only its shadowed side. Its face, when illuminated, also has a blotchy appearance, suggesting an uneven and variegated surface, such as earthy material often exhibits. And in fact, Anaxagoras declared that the surface of the moon was covered with mountains, plains, and valleys (which it is, but without a telescope one cannot see these features).[4]
What about the sun? It is always fiery in appearance, and, as we have noted, it must continue to radiate even when it is below the earth, for at the time of the full moon, the sun is 180⁰ from the moon in its orbit. When the full moon is at its zenith, the sun must be directly below the earth, and still shining, since it illuminates the moon all night long. We don’t get a clear account of how the sun shines from our sources on Anaxagoras. He suggests that the sun and the stars are fiery stones that might result either from some kind of friction or from being in the fiery aether (the reports are not clear).[5]
The meteor of Aegospotami was seen at the time a comet was burning in the sky.[6] This report may represent the first recorded appearance of Halley’s Comet, in 466 BCE.[7] According to Anaxagoras, comets are the conjunctions and perhaps collisions of planets or smaller stony bodies, asteroids, as we might say.[8] Such collisions might occasion the displacement of other asteroids, causing a meteor or meteor shower.
What is important in all of this was the Parmenides’ initial discovery of source of the moon’s light opened the doors of scientific inquiry to a series of interconnected theories, of eclipses, of meteors and asteroids, of comets and ultimately of heavenly motions in general. Anaxagoras’ account of the heavens entailed the existence of massive bodies spinning about the earth at high speeds. The theory of lighter-than-air heavenly bodies carried above the surface of the earth by a jetstream was replaced by the theory of a cosmic vortex that hurled great boulders and massive bodies by a kind of centrifugal force.[9] The cosmos was much greater in size and more powerful than early thinkers had imagined.
At the same time, we see the emergence of what philosopher of science Imre Lakatos (1978) called a Progressive Research Program, in which the program predicts new facts, so that one scientific advance begets another and another, and phenomena that had seemed inscrutable began to seem like the inevitable result of natural formations and lawlike interactions.
For the first time in Greek intellectual history, a philosopher speculating about nature actually explained correctly remote phenomena, and provided a framework within which other researchers made other discoveries that suggested further lines of inquiry. The success of Parmenides and his followers would be seen in the fact that henceforth, there were no new theories of lunar light proposed, and no new theories of eclipses. Virtually every later philosopher of nature would espouse the theories of Parmenides and Anaxagoras. Aristotle, indeed, would speak of their theories of heliophotism and antiphraxis as paradigms of scientific method, models of scientific explanation.
Whatever Parmenides set out to do, he sowed the seeds of empirical science. If he set out to demolish empirical science, he failed utterly but magnificently. If, on the other hand, he set out to provide a foundation for empirical science, he succeeded spectacularly.
[1] Pliny Natural History 2.149 = A11.
[2] Homer Iliad 4.25-27.
[3] Pliny Natural History 2.149-150 = A11; Plutarch Lysander 12.1-2 = A12.
[4] Hippolytus Refutation 1.8.10 = A42.
[5] Hippolytus 1.8.6-7; Plutarch Lysander 12.1-2.
[6] Pliny Natural History 2.149.
[7] See Graham and Hinz 2010.
[8] Aristotle Meteorology 342b 27-29 = A81.
[9] Anaxagoras fr. 12, fr. 13, fr. 15; Graham (2012).