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Answers to the question How did Kepler determine the orbital period of Mars? describing careful observations centuries ago got me thinking.

What was the first analysis of observations that directly demonstrated that the Sun and the outer giant planets were moving around a common barycenter rather than all planets rotating around a fixed Sun?

I am not sure if First observation that the movement of a planet or asteroid in its orbit was affected by another planet? is a completely separate question, or if this confirmation happened all at once, but I've currently asked it separately.

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  • $\begingroup$ I don't think so. Jupiter shouldn't be that massive to affect the Sun. It is only in rather large planet and small star systems where the affect can be noticed. I would rather think that the planets orbit the Sun in a point inside the star rather than an external barycenter. $\endgroup$ – Max0815 Feb 25 at 4:33
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    $\begingroup$ Hey @Max0815 Here's the swirly diagram of the solar system barycentre that uhoh mentioned. astronomy.stackexchange.com/a/28036/16685 $\endgroup$ – PM 2Ring Feb 25 at 6:45
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    $\begingroup$ @uhoh I'll need to look more into this. More complicated than I thought xD. $\endgroup$ – Max0815 Feb 26 at 20:14
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    $\begingroup$ @uhoh I don't know anything about this topic, and I can't to seem to find a source on this topic other than articles saying the barycenter is 1.07 solar radii. $\endgroup$ – Max0815 Feb 27 at 23:56
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    $\begingroup$ @Max0815 The 1.07 is only for the Sun-Jupiter system. The other large planets (Saturn, Uranus, Neptune) are not as heavy as Jupiter but they are farther out and the combined motion moves the Sun almost 2 solar radii at maximum. $\endgroup$ – uhoh Feb 28 at 0:04
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This idea would be a direct reduction from Newton's laws of motion. In his Principia he states "Hence the common centre of gravity of the earth, the sun, and all the planets, is to be esteemed the centre of the world". So that would be the first evidence of the Sun moving outside of a geocentric universe. Of course he wouldn't have known about Uranus and Neptune at the time.

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  • $\begingroup$ Thanks for your answer, but as I also mentioned in this comment I've asked for the first observation rather than the first realization. $\endgroup$ – uhoh Sep 1 at 20:41
  • $\begingroup$ You'll want to update the question then or post a new one, this one specifically asks for analysis of observations. $\endgroup$ – Greg Miller Sep 1 at 21:53
  • $\begingroup$ ...that directly demonstrated that the Sun and the outer giant planets were moving around a common barycenter. I have a hunch that the answer to my question will coincide with the first measurement of the mass of the Sun or more likely, the ratio of the masses of Jupiter and the Sun. If you'd like to specifically cite his analysis of solar parallax then that could be an answer, though it seems he was so far off it was probably just wrong. But just saying "Newton said in a book that they go around a common center" isn't enough. $\endgroup$ – uhoh Sep 1 at 23:44
  • $\begingroup$ just fyi, while the bounty expires in about 15 hours, there's a further 24 hour "grace period". $\endgroup$ – uhoh Sep 1 at 23:51
  • $\begingroup$ "Analysis of observations" and "Observations" are different things. Newtons entire Principia is about showing how his laws of motion fit to prior observations, just one conclusion of which is the solar system barrycenter. It sounds like you're looking for something else, so good luck. $\endgroup$ – Greg Miller Sep 2 at 1:29

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