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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.]]

The '''geocentric theory''' is a system for describing the universe on the basis that [[Earth]] lies at its center. 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.

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.

However, during the 1500s and 1600s, it became clear that the theory had some serious flaws in it. 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]].  The work of [[Johannes Kepler]] showed that planets had elliptical orbits. None of these observations could be adequately explained by a geocentric universe. When [[Isaac Newton]] applied his newly discovered [[gravitation|universal theory of gravitation]] to the data that Kepler collected, 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 considered to be profoundly mistaken, and the [[Heliocentrism|heliocentric theory]] correct.

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.

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.

== Scripture Quoted to justify Geocentric Theory ==

== Scripture Quoted to justify Geocentric Theory ==