This is a very naive question but I never fully understood this. For a system of two binary stars moving under the influence of their mutual gravitational forces revolve around their common center of mass. This is the "two-body problem" of undergraduate classical mechanics. However, from the perspective of observer A fixed in star A, star B revolves around it, and from the perspective of observer B fixed in star B, star A revolves around it. None of the observers is preferred. Then in what sense "earth moves around the Sun" is more accurate than the "Sun moves around the earth"?

  • $\begingroup$ We would tend to say both orbit in the gravitational field of the solar system, but this is dominated by the sun. Think of the motion of the centre of mass. $\endgroup$
    – James K
    Oct 22, 2021 at 5:32
  • $\begingroup$ @JamesK In what sense "the earth revolving around the sun" is more correct than saying the "sun revolving around the earth". $\endgroup$ Oct 22, 2021 at 5:35
  • $\begingroup$ Yes, I see. I think that is completely answered at the suggested other question. $\endgroup$
    – James K
    Oct 22, 2021 at 5:36
  • 4
    $\begingroup$ If we ignore the other planets, the Sun & Earth travel in elliptical orbits around the Sun-Earth barycentre. But the centre of the Sun is only ~450 km from that barycentre. $\endgroup$
    – PM 2Ring
    Oct 22, 2021 at 5:49
  • $\begingroup$ @PM2Ring you should make your comment a proper answer, because imho it is correct and exactly what OP was asking. However, I have seen this question asked a lot here on Astronomy SE. $\endgroup$ Oct 22, 2021 at 11:44


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