Editing Concentric spheres (section)

==Later additions to Eudoxus' model==
[[File:Eudoxus of Cnidus homocentric spheres model.png|thumb|Schematic model likely representing the first 4, out of a total of 27, spheres of Eudoxus' cosmic model following Giovanni Schiaparell. Each sphere has its own rotational axis that, together, generates a complex motion for the planet, in this illustration, the moon.]]
[[Callippus]], a contemporary of Eudoxus, attempted to improve his system by increasing the total number of homocentric spheres. He added two additional spheres for the sun and the moon as well as one additional sphere for Mars, Mercury, and Venus. These additional spheres were supposed to fix some of the calculation problems in Eudoxus’ original system. Callippus’ system was able to better predict the motions of certain celestial objects but his system still had many problems and was not able to account for many astronomical observations.<ref>{{cite book|last1=Dicks|first1=D.R.|title=Early Greek Astronomy to Aristotle|date=1985|publisher=[[Cornell University Press]]|location=Ithaca, NY|isbn=0801493102|pages=190–191}}</ref>

[[Aristotle]] developed his own system of concentric spheres in ''[[Metaphysics (Aristotle)|Metaphysics]]'' and [[On the Heavens|''De Caelo'' (On the Heavens)]]. He thought that both Eudoxus and Callippus had too few spheres within their models and added more spheres onto Callippus’ system. He added three spheres to Jupiter and Mars as well as four spheres to Venus, Mercury, the sun, and the moon for a total of fifty-five spheres. He later doubted the accuracy of his results and stated that he believed there were either forty seven or forty nine concentric spheres. Historians are unsure about how many spheres Aristotle thought there were in the cosmos with theories ranging from 43 to 55. Unlike Eudoxus, Aristotle believed that his system represented an actual model of the cosmos.<ref>{{cite journal|last1=Easterling|first1=H|title=Homocentric Spheres in De Caelo|journal=Phronesis|date=1961|volume=6|issue=2|pages=138–141|jstor=4181694|doi=10.1163/156852861x00161}}</ref>