Commentary Inf XVII 106-108

The extraordinary journey put fear into our hero, which he now may compare to that felt by classical precursors who failed on similar flights. As Brownlee points out, Phaeton (his story is found in Ovid, Metam. II.47-324) dropped the reins of his heavenly chariot as a result of his terror upon looking at the constellation Scorpio, while Dante mounts on the scorpion-tailed Geryon in order to accomplish his flight (Brow.1984.1), p. 136.

The 'scorching' of the sky, the path of Phaeton's fall, is the Milky Way. For Dante's dissimilarity to Phaeton see C.Inf.XXVI.19-24.