Author(s): Daniel Graham
Historians of science hold that the Presocratic philosophers had scientific attitudes but did not produce any empirical science and that the first Greek science, astronomy, did not develop until the time of Plato or later. This study argues that Presocratic philosophers made significant advances in the study of astronomy that deserve to be considered as scientific contributions. In the early fifth century BC, Parmenides recognized that the moon gets its light from the sun. Building on this insight, Anaxagoras developed a theory according to which the moon and other heavenly bodies were spherical masses, and eclipses were caused by the blocking of the sun’s light. When we compare cosmological theories of the sixth century BC with those of the fifth, we find that the former treated astronomical phenomena as continuous with meteorological events, while the latter treated heavenly bodies as independent stony masses whirled in a cosmic vortex. Two historic events help to date and account for the change: a solar eclipse in 478 BC, and a meteoroid that fell to earth at the time a comet was visible, around 466. Both events are linked to Anaxagoras. There is evidence that Anaxagoras’ theory, together with the heavenly events that “confirmed” it, changed philosophers’ conceptions of the cosmos. After Anaxagoras, virtually all philosophers accepted his theory of lunar light. Aristotle held up Anaxagoras’ theory of eclipses as a paradigm of scientific explanation. These principles mark the beginning of a geometrical treatment of astronomy, and have been accepted by astronomers ever since.