This medieval illustration of the Ptolemaic system, which follows the system of Aristotle and ows much to the idea of harmonic spheres of Pythagoras, shows the arrangement of the planets surrounded by the sphere of the stars and the "prime mover" which provides the energy for the movement of all other spheres (see below for an explanation of the Latin names):
Decimum Coelum Primu(m) Mobile = 10th sky (sphere), prime mover
Nonu(m) Coelum Crystallinum = 9th sky (sphere) of crystal
Octavium (coleum) Firmamentu(m) = 8th sky (sphere), firmament (of the stars)
COELV (COELUM) = sky (sphere) of:
SATURNI = Saturn
IOVIS = Jupiter
MARTIS = Mars
SOLIS = Sun
VENERIS = Venus
MERCURII = Mercury
LUNAE = Moon