eli5: If every frame of reference is valid, why do people say the earth spins around the sun instead of the opposite, wouldn’t both views be equally valid?

Question

eli5: If every frame of reference is valid, why do people say the earth spins around the sun instead of the opposite, wouldn’t both views be equally valid?

In: Physics

Answer 1

If you’re only considering the sun and the earth, then for purposes of calculations and whatnot, both are equally valid.

When you start including more stuff into the mix, then things get complicated. If the earth is stationary, and it’s the sun that’s moving… then all the *other* planets in the solar system are also moving. Not only that, but the field of stars we see at night must *also* be moving… and not just moving, but moving at a tremendous, impossibly-fast speed given their distance to the earth. The only way that you can see the same starfield every night, filled with stars so far away, is if those stars are moving *faster than the speed of light*, and we know they aren’t, so…