Relativity doesn't agree with you. Relativity says you can use a frame centered on the Earth if you like. It makes your description of the motions of the Sun, M

Relativity doesn't agree with you. Relativity says you can use a frame centered on the Earth if you like. It makes your description of the motions of the Sun, Moon, and planets more complicated, which is why astronomers don't do it--why complicate things if you don't need to? But it's still a perfectly valid viewpoint as far as relativity is concerned. In fact, astronomers today don't even use a "heliocentric" frame--they use a barycentric frame, i.e., the spatial origin is the barycenter of the solar system. The Sun is of course much closer to the barycenter than any other body, but it's not exactly at it.