It is generally held that Presocratic cosmologies are sui generis and unique to their authors. If, however, a division is made between sixth-century and fifthcentury BC cosmologies, some salient differences emerge. For instance, heavenly bodies in sixth-century cosmologies tend to be light, ephemeral, fed by vapors, and located above the earth; those in fifth-century cosmologies tend to be heavy, permanent, heated by friction, and to travel below the earth. The earlier cosmologies seem to embody a meteorological model of astronomy, the latter a lithic model. The change in models can be accounted for on the basis of Parmenides’ discovery that the moon is illuminated by the sun and hence is a spherical, permanent, opaque or earthy body. This insight generated empirical evidence to confirm itself and rendered obsolete earlier cosmologies.