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Line 1: − The '''geocentric theory''' in [[Astronomy]] is a system for describing the universe with Earth-centered coordinates.<ref>The 1911 Encyclopedia Britannica defined geocentric as "referred to the centre of the earth as an origin; a term designating especially the co-ordinates of a heavenly body referred to this origin."</ref> It was extremely popular from ancient times until the 1600s, as it had better agreement with observation than any alternative. [[Ptolemy]]'s model was particularly effective at cosmological predictions. − + + + + + + + + + + + + +
improved introduction
[[Image:Ptolemaicsystem-small.png|right|thumb|Rendition of a geocentric system from the Middle Ages.]]
[[Image:Ptolemaicsystem-small.png|right|thumb|Rendition of a geocentric system from the Middle Ages.]]
By the 1800s, the spectacular successes of Newtonian theory and [[Maxwell's equations]] for electromagnetism had convinced everyone that the Sun is a preferred frame of reference, and that the laws of physics must be applied in that frame. The geocentric theory was considered to be profoundly mistaken, and the [[Heliocentrism|heliocentric theory]] correct.
A '''Geocentric theory''' is a astronomical theory which describes the universe as a ''Geocentric system'', i.e., a system which put the Earth in the center of the universe, or at least in the center of the solar system.
The Greek philosophers Aristotle and Plato described such a theory wherein all celestial bodies move on spheres around the earth, the moon of the innermost one, the fix stars of the one most out.
==Ptolemy's system==
Ptolemy invented the most elaborated geocentrical system, allowing the planets not only to move on circles around the earth, but using epicycles. By adding further ideas, he was able to predict the motion of the planets quite well. Ptolemy's model was extremely popular from ancient times until the 1600s, as it had better agreement with observation than any alternative. His model was particularly effective at cosmological predictions.
However, during the 1500s and 1600s, it became clear that the theory had some serious flaws in it. The [[Denmark|Danish]] astronomer [[Tycho Brahe]] made the most accurate observations possible before the invention of the telescope. These showed discrepancies within Ptolemy's system.
With the invention of the [[telescope]], the observations became more precise, and new phenomena were discovered: In particular, [[Galileo]]'s use of the [[telescope]] to look at the skies revealed that [[Jupiter]] had at least four moons, and Venus had phases like the [[Moon]]: both phenomena were at odds with Ptolemy's model.
[[Johannes Kepler]] used Brahe's measurements to improve the [[Heliocentrism|heliocentric]] system Copernicus had proposed, showing that planets had elliptical orbits around the sun. When [[Isaac Newton]] applied his newly discovered [[gravitation|universal theory of gravitation]] to the data, he found that a heliocentric model was the only one that could explain all observed phenomena. By the 1800s, the spectacular successes of Newtonian theory and [[Maxwell's equations]] for electromagnetism had convinced practically everyone that the Sun is a preferred frame of reference, and that the laws of physics must be applied in that frame. The geocentric theory was finally considered to be profoundly mistaken.
Since the advent of relativity theory in the early 1900s, the laws of physics have been written in covariant equations, meaning that they are equally valid in any frame. Heliocentric and geocentric theories are both used today, depending on which allows more convenient calculations.
Since the advent of relativity theory in the early 1900s, the laws of physics have been written in covariant equations, meaning that they are equally valid in any frame. Heliocentric and geocentric theories are both used today, depending on which allows more convenient calculations.