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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 with Earth-centered coordinates. It was extremely popular from ancient times until about 1690, as it had better agreement with observation than any alternative. Ptolemy's model was particularly effective at cosmological predictions.
The '''geocentric theory''' is a system for describing the universe with Earth-centered coordinates. It was extremely popular from ancient times until the 1600s, as it was particularly effective at cosmological predictions.
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.
The work of [[Galileo]] and [[Kepler]] began to change this (see [[Copernican Revolution]]). The idea that planets move around the sun, in nearly circular ellipses, gradually took hold. The difficulty of calculating the orbits was one factor which militated against quick acceptance of Kepler's laws of motion.
By the 1800s, the spectacular successes of Newtonian theory 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 [[covariance|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 [[covariance|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.
[[Category:Astronomy]]
[[Category:Astronomy]]