 As in the case of Philolaus’ cosmogony, there is considerable controversy about the precise nature of Philolaus’ astronomy. The a priori features, as well as other testimonia stating that Philolaus believed that the moon was inhabited by creatures fifteen times more powerful than those on the earth (Aetius 2.30.1 = DK 44 A20), have suggested to some that Philolaus’ system is largely a fantasy and has nothing to do with empirical astronomy (Furley 1987, 58). Burkert argues, moreover, that the apparent coherence of the astronomical system is destroyed, because the fixed stars, which serve as the backdrop for the motions of the heavenly bodies described above, were not in fact stationary but moved with the fastest motion so that, without a fixed backdrop, the whole system dissolves into chaos (1972a, 340); he argues that Philolaus’ astronomy is primarily of mythological and religious significance (1972a, 348). However, more recent assessments argue that Philolaus’ astronomical system was a serious attempt to account for the phenomena and the most successful such attempt of his time (Huffman 1993: 231–288; Graham 2015). The text on which Burkert relied to conclude that the fixed stars have the fastest motion is, in fact, part of a speculative reconstruction of the doctrine of the harmony of the spheres by a later Greek commentator, Alexander of Aphrodisias, and not a description of Philolaus’ system. Nor need speculation about the inhabitants of the moon indicate that the system is fantastical, since such staid Presocratic rationalists as Anaxagoras also argued that the moon was inhabited (see D.L. II 8 and DK 59 A77). Perhaps the strongest reason for believing that Philolaus’ astronomical system was at least in part an attempt to explain the phenomena rather than just of religious and mythological significance is that other thinkers made objections to the system on empirical grounds, and Philolaus responded to those criticisms in ways that attempted to show that his system could explain or “save” the phenomena. Thus an obvious objection to the system is that we never observe the central fire at the center of the universe. Philolaus explained this by supposing that the earth rotates once on its axis as it orbits the central fire, so that our side of the earth is always turned away from the central fire and hence we never see it. This is also why we never see the counter earth, which is evidently supposed to move at the same speed as the earth. An objection to the moving earth was raised on the grounds that the parallax produced by its movement from one side to the other of the central fire would cause the sun, moon and planets to appear to move in ways in which they do not. Philolaus evidently argued that the diameter of the earth’s orbit was so small relative to the distance to the other heavenly bodies that the parallax effects would be negligible (De Caelo 293b25–30). It is not clear that this solves the problem, but if the system is solely of mythic or religious significance it is odd that other thinkers, including Aristotle, treated the system as if it were supposed to be consistent with the phenomena, and even more surprising that Philolaus tried to defend the system by showing that it was consistent with those phenomena. Moreover, as mentioned above, Graham has recently shown that the counter-earth is not introduced just for a priori reasons but serves to give the most sophisticated account of lunar eclipses of the time (Graham 2015).