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I know that describing the trajectory of all planets in the solar system around the Earth is much more complicated than if we take the Sun as the reference point. But besides this, what is the simplest experiment that can prove that the Sun is a more "inertial" point of reference than the Earth? Do we have to look at the stars in the background or something like that?


marked as duplicate by John Rennie, ja72, tpg2114, David Z Nov 10 '13 at 23:53

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  • $\begingroup$ "Do we have to look at the stars in the background or something like that?" -- the yearly paralax is a good proof, but why aren't you satisfied by the laws of conservation? $\endgroup$ – John Dvorak Nov 10 '13 at 19:57

In fact, if our system consists of only earth and sun, we'd never ever know, because we can never measure the difference, since you can always change the frame of reference between earth and sun, and both statements will be true (earth goes around the sun or vice-versa).

That's why, you need a third impartial object, which typically is a star far, far away. The star gives some light, and we can measure the light abberation caused by the earth's movement, and that's how we know.

  • $\begingroup$ We don't need stars for this. Other planets will do. $\endgroup$ – Brandon Enright Nov 11 '13 at 0:02
  • $\begingroup$ @BrandonEnright I disagree. Using other planets would mean that there's a kind of interaction with those planets we can measure, and the only thing I can think about is the hypothetical gravitational waves that come from other planets, which are not measureable (so far). So in principle, if there's a measurable interaction between our planet and the other planets, then other planets shall suffice; but this is not the case, and the measureable interaction is light, which doesn't come from other planets. Please correct me if I'm wrong. $\endgroup$ – The Quantum Physicist Nov 11 '13 at 8:06
  • $\begingroup$ Of course there is a measurable interaction. Light from the sun reflects off the planets and to us. They look pretty much like stars but that don't move like stars. The phases of Venus was one of the last nails in the coffin of the geocentric model. Even if there were no other stars in the universe we'd still know that we (and the rest of the planets) orbit the sun. $\endgroup$ – Brandon Enright Nov 11 '13 at 20:41

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