Aristotle In the field of astronomy Aristotle was responsible for the notion that the spheres which carried the heavenly bodies round their courses were real physical bodies, not mere geometrical constructions as Eudoxus had supposed. Each sphere passed on its motions to the sphere immediately below it so that outermost sphere carrying the fixed stars, by rotating daily upon its axis, caused the diurinal rotation of all the spheres and the heavenly bodies attached to them with it. In order that the motions peculier to one heavenly body should not be passed on to the body immediately below it, Aristotle inserted that a number of unrolling spheres between each set of spheres carrying a planet. According to Aristotle, the outermost sphere of the fixed stars was moved by the Primum Mobile or the Unmoved Mover at the periphery of the universe which goverened all the spheres and universe as a whole. He seemed to have suggested also that each of the other spheres had a lesser unmoved mover which was responsible for the particular motion of the sphere. The movers were spiritual in charachter, the relation of a mover to its related sphere akin to that of a soul to a body. The mover of a planet worked against the primum Mobile so that the planets had their own west to east motions contrary to the diurinal rotation. The outermost planet, Saturn, had the greatest difficulty in overcoming the Primum Mobile and so had the longest period of rotation, while the innermost body, the moon, had the shortest. Thus Aristotle, like Plato, arranged the heavenly bodies in order outwards from the earth according to their apparant periods of revolution, namely the Moon, Sun, Venus, Mercury, Mars, Jupiter, and Saturn.
Posted on: Thu, 01 Aug 2013 20:02:23 +0000
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