Celestial Spheres

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 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. Since the fixed stars did not change their positions relative to each other, it was argued that they must be on the surface of a single starry sphere.

In modern thought, the orbits of the planets define the paths of those planets through mostly empty space. Ancient and medieval thinkers, however, considered the celestial orbs to be thick spheres of rarefied matter nested one within the other, each one in complete contact with the sphere above it and the sphere below. When scholars applied Ptolemy's epicycles, they presumed that each planetary sphere was exactly thick enough to accommodate them. By combining this nested sphere model with astronomical observations, scholars calculated what became generally accepted values at the time for the distances to the Sun (about 4 million miles), to the other planets, and to the edge of the universe (about 73 million miles). The nested sphere model's distances to the Sun and planets differ significantly from modern measurements of the distances, and the size of the universe is now known to be inconceivably large and possibly infinite.

Albert Van Helden has suggested that from about 1250 through the Seventeenth Century, virtually all educated Europeans were familiar with the Ptolemaic model of "nesting spheres and the cosmic dimensions derived from it". Even following the adoption of Copernicus's heliocentric model of the universe, new versions of the celestial sphere model were introduced, with the planetary spheres following this sequence from the central Sun: Mercury, Venus, Earth-Moon, Mars, Jupiter and Saturn.

Read more about Celestial SpheresHistory, Literary and Symbolic Expressions

Other articles related to "celestial spheres, spheres, celestial":

Unmoved Mover - First Philosophy - Celestial Spheres
... arising from uniform circular motions of celestial spheres ... While the number of spheres in the model itself was subject to change, (47 or 55), Aristotle's account of aether, and of potentiality and actuality, required an individual unmoved mover ...
ʿAjā'ib Al-makhlūqāt Wa Gharā'ib Al-mawjūdāt - Cosmography
... the celestial spheres) ... Qazwini’s cosmography consists of two parts, the first dealing with the spheres of the heaven with its inhabitants (the angels) and the details of the Islamic, Roman and Iranian ... The second part discusses the four elements, the spheres and what is on and in the earth, in addition to this Qazwini talks in detail about man, the faculties of his ...
Celestial Spheres - Literary and Symbolic Expressions
... "The spheres... 99 In Cicero's Dream of Scipio, the elder Scipio Africanus describes an ascent through the celestial spheres, compared to which the Earth and the Roman Empire dwindle into ... a discussion of the various schools of thought on the order of the spheres, did much to spread the idea of the celestial spheres through the Early Middle Ages ...
Cosmology In Medieval Islam - Cosmology in The Medieval Islamic World - Experimental Astrophysics and Celestial Mechanics
... ibn Mūsā ibn Shākir, made significant contributions to Islamic astrophysics and celestial mechanics ... He was the first to hypothesize that the heavenly bodies and celestial spheres are subject to the same laws of physics as Earth, unlike the ancients who ... Ibn al-Haytham, in his Book of Optics (1021), was also the first to discover that the celestial spheres do not consist of solid matter, and he also discovered that the ...

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