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The celestial spheres, or celestial orbs, were the fundamental entities of the cosmological models developed by Plato, Eudoxus, Aristotle, Ptolemy, Copernicus, and others. In these celestial models, the apparent motions of the fixed stars and planets are accounted for by treating them as embedded in rotating spheres made of an aetherial ...
Thomas Aquinas (c. 1225 –1274), following Avicenna, interpreted Aristotle to mean that there were two immaterial substances responsible for the motion of each celestial sphere, a soul that was an integral part of its sphere, and an intelligence that was separate from its sphere. The soul shares the motion of its sphere and causes the sphere ...
Visualization of a celestial sphere. In astronomy and navigation, the celestial sphere is an abstract sphere that has an arbitrarily large radius and is concentric to Earth.All objects in the sky can be conceived as being projected upon the inner surface of the celestial sphere, which may be centered on Earth or the observer.
Aristotelian physics is the form of natural philosophy described in the works of the Greek philosopher Aristotle (384–322 BC). In his work Physics, Aristotle intended to establish general principles of change that govern all natural bodies, both living and inanimate, celestial and terrestrial – including all motion (change with respect to place), quantitative change (change with respect to ...
The cosmological model of concentric (or homocentric) spheres, developed by Eudoxus, Callippus, and Aristotle, employed celestial spheres all centered on the Earth. [1] [2] In this respect, it differed from the epicyclic and eccentric models with multiple centers, which were used by Ptolemy and other mathematical astronomers until the time of Copernicus.
Aether naturally moved in circles, and had no contrary, or unnatural, motion. Aristotle also stated that celestial spheres made of aether held the stars and planets. The idea of aethereal spheres moving with natural circular motion led to Aristotle's explanation of the observed orbits of stars and planets in perfectly circular motion. [1] [11]
The sublunary sphere was the realm of changing nature. Beginning with the Moon, up to the limits of the universe, everything (to classical astronomy) was permanent, regular and unchanging—the region of aether where the planets and stars are located. Only in the sublunary sphere did the powers of physics hold sway. [3]
Aristotle theorized that aether did not exist anywhere on Earth, but that it was an element exclusive to the heavens. As substances, celestial bodies have matter (aether) and form (a given period of uniform rotation). Sometimes Aristotle seems to regard them as living beings with a rational soul as their form [2] (see also Metaphysics, bk. XII).