Editing Geocentric model (section)

==Ancient Greece==
[[File:Persectives of Anaximander's universe.png|thumb|upright=1.35|Illustration of Anaximander's models of the universe. On the left, summer; on the right, winter.]]

In the 6th century BC, [[Anaximander]] proposed a cosmology in which Earth is shaped like a section of a pillar (a cylinder), held aloft at the center of everything. The Sun, Moon, and planets were holes in invisible wheels which surround Earth, and through those holes, humans could see concealed fire. At around the same time, [[Pythagoras]] thought that Earth was a sphere (in accordance with observations of eclipses), but not at the center; he believed that it was in motion around an unseen fire. Later these two concepts were combined, so that most of the educated Greeks from the 4th century BC onwards thought that Earth was a sphere at the center of the universe.<ref name= "Fraser2006"/>

In the 4th century BC [[Plato]] and his student [[Aristotle]], wrote works based on the geocentric model{{cn|date=January 2025}}. According to Plato, the Earth was a sphere, stationary at the center of the universe. The stars and planets were carried around the Earth on [[Celestial spheres|spheres or circles]], arranged in the order (outwards from the center): Moon, Sun, Venus, Mercury, Mars, Jupiter, Saturn, fixed stars, with the fixed stars located on the celestial sphere. In his "[[Myth of Er]]", a section of the ''[[Republic (dialogue)|Republic]]'', Plato describes the cosmos as the [[Spindle of Necessity]], attended by the [[Siren (mythology)|Sirens]] and turned by the three [[Moirai|Fates]]. [[Eudoxus of Cnidus]], who worked with Plato, developed a less mythical, more mathematical explanation of the planets' motion based on Plato's [[dictum]] stating that all [[phenomena]] in the heavens can be explained with uniform circular motion. Aristotle elaborated on Eudoxus' system.

In the fully developed Aristotelian system, the spherical Earth is at the center of the universe, and all other heavenly bodies are attached to 47–55 transparent, rotating spheres surrounding the Earth, all concentric with it. (The number is so high because several spheres are needed for each planet.) These spheres, known as crystalline spheres, all moved at different uniform speeds to create the revolution of bodies around the Earth. They were composed of an incorruptible substance called [[Aether (classical element)|aether]]. Aristotle believed that the Moon was in the innermost sphere and therefore touches the realm of Earth, causing the dark spots ([[Macula (planetary geology)|maculae]]) and the ability to go through [[lunar phases]]. He further described his system by explaining the natural tendencies of the terrestrial elements: earth, water, fire, air, as well as celestial aether. His system held that earth was the heaviest element, with the strongest movement towards the center, thus water formed a layer surrounding the sphere of Earth. The tendency of air and fire, on the other hand, was to move upwards, away from the center, with fire being lighter than air. Beyond the layer of fire, were the solid spheres of aether in which the celestial bodies were embedded. They were also entirely composed of aether.

Adherence to the geocentric model stemmed largely from several important observations. First of all, if the Earth did move, then one ought to be able to observe the shifting of the fixed stars due to [[stellar parallax]]. Thus if the Earth was moving, the shapes of the [[constellation]]s should change considerably over the course of a year. As they did not appear to move, either the stars are much farther away than the Sun and the planets than previously conceived, making their motion undetectable, or the Earth is not moving at all. Because the stars are actually much further away than Greek astronomers postulated (making angular movement extremely small), [[stellar parallax#Early theory and attempts|stellar parallax]] was not detected [[stellar parallax#19th and 20th centuries|until the 19th century]]. Therefore, the Greeks chose the simpler of the two explanations. Another observation used in favor of the geocentric model at the time was the apparent consistency of Venus' luminosity, which implies that it is usually about the same distance from Earth, which in turn is more consistent with geocentrism than heliocentrism. (In fact, Venus' luminous consistency is due to any loss of light caused by its phases being compensated for by an increase in apparent size caused by its varying distance from Earth.) Objectors to heliocentrism noted that terrestrial bodies naturally tend to come to rest as near as possible to the center of the Earth. Further, barring the opportunity to fall closer the center, terrestrial bodies tend not to move unless forced by an outside object, or transformed to a different element by heat or moisture.

Atmospheric explanations for many phenomena were preferred because the Eudoxan–Aristotelian model based on perfectly concentric spheres was not intended to explain changes in the brightness of the planets due to a change in distance.<ref name= "Hetherington2006"/> Eventually, perfectly concentric spheres were abandoned as it was impossible to develop a sufficiently accurate model under that ideal, with the mathematical methods then available. However, while providing for similar explanations, the later [[deferent and epicycle]] model was already flexible enough to accommodate observations.