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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, strictly speaking, the view that the sun is at the center of the universe, though it is now generally understood to mean only that the sun is the center of the solar system. 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. It is now accepted that the real controversy is whether the sun or the Earth is the center of the solar system, or, in simpler terms, whether the sun goes around the Earth or the Earth goes around the sun.  The Copernican revolution established the latter; the former is often attributed to [[Ptolemy]].

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.

 

::''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.''

 

While they are equivalent in an abstract sense of Newtonian/Galilean relativity, that fact is useless in practice.  One generally uses a coordinate system that is inertial, or nearly so, for the calculations that one is making.

*For ordinary activities on Earth, such as walking or driving one's car, a co-rotating geocentric system is the one to use.  It doesn't matter which of the sun or the Earth goes around the other.  But the Coriolis force does figure into very accurate calculations for airplanes, missiles, and artillery guns.  It may also have been involved in the outcome of a [http://ftw.usatoday.com/2015/10/neil-degrasse-tyson-bengals-kicker football game].

*For calculations involving artificial Earth satellites, a non-rotating Earth-based coordinate system is the one to use.

*For calculations of planetary motions and interplanetary spacecraft, a non-rotating sun-based coordinate system (that is, Copernican heliocentric) is the one to use.  Calculation of planetary motions was what led to the Copernican formulation.

*For galactic calculations, it doesn't really matter.

==References==

==References==