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[[File:Heliocentric.jpg|thumb|Illustration of the [[Nicolaus Copernicus|Copernican system]] by Andreas Cellarius]]

[[File:Heliocentric.jpg|thumb|Illustration of the [[Nicolaus Copernicus|Copernican system]] by Andreas Cellarius]]

'''Heliocentrism''' is the view that the sun is at the center of the universe. It was proposed by some ancient Greeks,<ref>Aristarchus of Samos (ca. 310-230 BC) proposed it, Archimedes discussed it, and the idea was well-known in Europe when [[Copernicus]] proposed a heliocentric model. [http://galileo.rice.edu/sci/theories/copernican_system.html]</ref>, but it never gained wide support because its proponents could not explain why the relative positions of the stars seemed to remain the same despite the Earth’s changing angles of perspective as it revolved about the Sun.<ref>http://www.britannica.com/EBchecked/topic/260027/heliocentric-system</ref> It became the dominant view in the 1700s and 1800s. The idea that the sun is at the center of the ''universe'', was abandoned by the mid 20th century.  

'''Heliocentrism''' is the view that the sun is at the center of the universe. It was proposed by some ancient Greeks,<ref>Aristarchus of Samos (ca. 310-230 BC) proposed it, Archimedes discussed it, and the idea was well-known in Europe when [[Copernicus]] proposed a heliocentric model. [http://galileo.rice.edu/sci/theories/copernican_system.html]</ref>, but it never gained wide support because its proponents could not explain why the relative positions of the stars seemed to remain the same despite the Earth’s changing angles of perspective as it revolved about the Sun.<ref>http://www.britannica.com/EBchecked/topic/260027/heliocentric-system</ref> It became the dominant view in the 1700s and 1800s. The idea that the sun is at the center of the ''universe'' was abandoned by the mid 20th century.  

Since the advent of [[theory of relativity|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 theory|geocentric]] plotting systems are both used today, depending on which allows more convenient calculations. Heliocentric coordinates have the advantage of being closer to an [[inertial reference frame]].

Since the advent of Galilean and Newtonian mechanics, and particularly Galilean relativity, in the 1600s, the laws of physics have been written in covariant equations, meaning that they are equally valid in any frame. Heliocentric and [[Geocentric theory|geocentric]] plotting systems are both used today, depending on which allows more convenient calculations. Geocentric coordinates are obviously the right system to use for travelling on Earth.  Heliocentric coordinates are used for interplanetary spacecraft.  They also have the advantage of being closer to an [[inertial reference frame]], though the difference is so tiny as to be negligible.  [[theory of relativity|Einsteinian relativity]] is not needed.

==References==

==References==