The Superior Planets
Having developed the theories of the Sun and Moon with the theory of eclipses as a beautiful corollary, and having described the fixed stars, Ptolemy now turns to the theory of the remaining planets - Saturn, Jupiter, Mars, Mercury, and Venus. They are dealt with in Book IX-XI of the Almagest. The old question of the order of the planets (page 295) is raised at the beginning [IX, 1; Hei 2, 206], where Ptolemy has to admit that there are no objective criteria of planetary distances because of the imperceptible planetary parallaxes. Nevertheless, he thinks it the best course to follow those ancient astronomers who placed the sphere of the Sun in the middle, with Saturn, Jupiter, and Mars above it as superior planets, and Venus, Mercury, and the Moon below it. Mercury and Venus are therefore known as the inferior planets. This has the advantage that the sphere of the Sun divides the planets into two natural groups, the superior having oppositions, and the inferior not.