Aristotle's Initial Model Of The Universe Essay

Juan Anton D. de los Reyes

Ph.157.4A

Aristotle’s initial model of the universe was that of a gigantic sphere, of which the earth is the core. Other spheres circumscribe the earth, and, with the exception of the innermost sublunary circles, these rotate in the westward direction of the outermost sphere, returning to their original angles in a span of twenty-four hours. The sublunary circles, in increasing proximity from the earth, are comprised of the Greek elements of water, air, and fire. The fourth to ninth circles contain the planets Moon, Sun, Mercury, Venus, Mars, Jupiter, and Saturn, respectively. The outermost circle, called the primum mobile, carries the stars and the other heavenly bodies. The rotation of an outer sphere, in this model, is what influences the movement of an inner sphere—the movement of an inner circle is influenced by the circle directly above it. After a while, however, Aristotle realized a few points of error in this overly simplistic system. He saw it odd for the lagging movement each circle to be influenced by that of an outer circle, conveniently forming a 23.5º angle (de Schrijver, 26-7).

He deviated from this original model and studied others in search of an answer,

Another man, Callippus, contributed to this model, and added two more spheres to each of the Sun and Moon, and one more to each of Mercury, Venus and Mars. Aristotle accepted the concepts derived from these models, adding four neutralizing spheres to each of the Sun and all planets outside it, besides Saturn to which he only added three spheres. This would account for how the Sun’s movement was seemingly uninfluenced by the movement of outer planets, such as Saturn and Mercury. The new total of 55 spheres would account for how each inner planet’s movement was independent of the planet above it (de Schrijver,