The Celestial Sphere

 The celestial spheres, or celestial orbs, were the fundamental celestial entities of the cosmological celestial mechanics first invented by Eudoxus, adopted by Aristotle and developed by Ptolemy, Copernicus and others. In this celestial model the stars and planets are carried around by being embedded in rotating spheres made of an aetherial transparent fifth element (quintessence), like jewels set in orbs. 

In geocentric models the spheres were most commonly arranged outwards from the center in this order: the sphere of the Moon, the sphere of Mercury, the sphere of Venus, the sphere of the Sun, the sphere of Mars, the sphere of Jupiter, the sphere of Saturn, the starry firmament, and sometimes one or two additional spheres. 

The order of the lower planets was not universally agreed: Plato and his followers ordered them Moon, Sun, Mercury, Venus, and then followed the standard model for the upper spheres; there were other disagreements about the relative place of the spheres of Mercury and Venus...<<<Read More>>>...