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[[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.]]

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.

A '''Geocentric theory''' is a long superseded astronomical theory which describes the universe as a ''Geocentric system'', i.e., a system which puts the Earth in the center of the universe, or in the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.

The Greek philosophers Aristotle and Plato described such a theory wherein all celestial bodies move on spheres around the earth, the moon on the innermost one and the fixed stars on the outermost one.

==Ptolemy's system==

==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.

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.

However, during the 1500s and 1600s, it became clear that geocentrism 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.  

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.

[[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 has been considered to be profoundly mistaken for the last few centuries.

 

 

 

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.

== Scripture Quoted to justify Geocentric Theory ==

== Scripture Quoted to justify Geocentric Theory ==

A few [[Bible]] quotes use geocentric terms.  While some attempt to use these quotes to discredit the Bible's hold on science, others dispute this usage, claiming that the usage of the terms is similar to the way people today use terms like "sunrise" and "sunset".  In this account, the terminology is not wrong - merely reflects the observer's view.

A few [[Bible]] quotes use geocentric terms.  While some attempt to use these quotes to discredit the Bible's hold on science, others dispute this usage, claiming that the usage of the terms is similar to the way people today use terms like "sunrise" and "sunset".  In this account, the terminology is not wrong, but merely reflects the observer's view.

*"He has fixed the earth firm, immovable." (1 Chronicles 16:30)

*"He has fixed the earth firm, immovable." (1 Chronicles 16:30)