So the planets, note and pitch going from lowest to highest planetary position (which is also the highest to lowest musical position) are as follows:

Moon, nete, D
Venus, paranete, C
Mercury, paramese or trite, Bb
Sun, mese, A
Mars, lichanos or hypermese, G
Jupiter, parahypate, F
Saturn, hypate, E

This scheme was laid out as a kind of celestial ladder. Centuries later, when alchemy was all the rage, the celestial ladder was an extremely important part of its doctrines. If we arrange an ascending scale (from the Italian scala or "ladder") from the celestial ladder, we obtain two tetrachords:

E F G A Bb C D

From E to A is a perfect 4th interval and from A to D is another. A perfect 4th is 5 half-steps. So in all we have 10 half-steps here—a minor 7th. Since a perfect octave has 12 half-steps, we are a whole step shy of an octave and this makes sense because a full octave would be perfect 4th and its inverse the perfect 5th. Five and seven half-steps added together give us the full 12-half tone octave. Here, however, we are only concerned with the 7 diatonic notes called a heptachord. But why go from A to Bb since there is a natural half-step between B and C? Because the pattern of each tetrachord is half-step/whole step/whole step. The common note between each tetrachord being A – mese or the sun. Mese is where we get the prefix "Meso-" or middle.