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This question already has an answer here:

What if somebody says that Sun orbits around the Earth and not Earth orbiting around the Sun?

What would be the consequences?

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marked as duplicate by John Rennie, Valter Moretti, DavePhD, jinawee, Kyle Kanos Jun 10 '14 at 13:13

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

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    $\begingroup$ possible duplicate of Geocentric Model in General Relativity $\endgroup$ – John Rennie Jun 10 '14 at 9:35
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    $\begingroup$ It is not duplicate in my view, since here the question does not mention GR and an answer can be given sticking to classical dynamics. $\endgroup$ – Valter Moretti Jun 10 '14 at 9:37
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    $\begingroup$ I do not understand the -1 vote: This is an important question even at epistemological level. $\endgroup$ – Valter Moretti Jun 10 '14 at 10:12
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    $\begingroup$ There is another duplicate Why do we say that the earth moves around the sun? that doesn't involve GR. Anyhow, the question I linked states That accelerated reference frame causes all sorts of messy fictitious forces that push the stars and planets around, which answers this question. $\endgroup$ – John Rennie Jun 10 '14 at 10:13
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    $\begingroup$ Downvote: because "consequences" is vapid. It could mean, as I would say, that the math defining the paths followed in space by the sun and earth (and planets) would get really ugly. Or it could mean "OMG maybe religion is real after all". Or it could mean, that there would be literal consequences for the person who said that, such as getting thrown out of his physics class for being terminally nuts. $\endgroup$ – Carl Witthoft Jun 10 '14 at 11:56
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The earth and sun revolve around a "barycenter" BUT since the earth and sun are NOT a "2 body system" the actual, exact, precise barycenter is impossible to calculate or predict. It is NOT incorrect to say the earth revolves around the sun...

A pair of bodies in space revolve around their mutual center of gravity, called the barycenter.

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The issue can be tackled in Newtonian physics, more precisely in Newtonian dynamics.

As motion is a relative notion, there is no hope to answer exploiting kinematic notions only (I am referring to the case where only Sun and Earth are present. If including other planets, the situation would become more complicated, but more details should be added to the question to answering it).

The issue involves the notion of inertial frame. The question may be paraphrased as follows:

Is it possible to fix an inertial reference frame where the Sun (the Earth) is viewed rotating around the Earth (respectively the Sun)?

Both possibilities are actually false. However, as the mass of the Sun is hugely grater than the one of the Earth, the centre of mass of the system which, in view of dynamical laws stays at rest in an inertial frame, is very close to the sun.

The fact that the rest frame of the Earth is not an inertial one implies that the motion of bodies described from an observers at rest with the Earth needs apparent forces to be dynamically explained. For instance, these forces do not verify the action-reaction principle and, in general they have no material cause as, instead, real forces have. So answering that question involves some nontrivial theoretical ideas.

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Saying the sun rotates around the earth is equally valid to saying the earth rotates around the sun, or any more cumbersome viewpoint. Any frame of reference is equally valid.

However, if you are to calculate and predict the motions of the planets, you are far better off by using the heliocentric frame, because in the geocentric one you will have planets moving backwards from time to time.

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  • $\begingroup$ I was asking about the consequences $\endgroup$ – Florescent Ticker Jun 10 '14 at 10:05
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What about the stars? Do they also rotate around the earth? I think they would have to, otherwise you need the earth rotating, so that the stars appear to move round the earth. If so we are back to the old pre copernican view of the earth being a special body in the universe.

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    $\begingroup$ This is not an answer to the question. It should be posted as a new question or a comment on another post. $\endgroup$ – Jim Jun 10 '14 at 15:51
  • $\begingroup$ It is an answer, but in the form of a question. If the sun revolves around the earth, one consequence is you have to think about how the stars move around the earth, if at all. Perhaps you could reconsider the negative score? $\endgroup$ – Dr Chuck Jun 10 '14 at 19:33

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