There are of course many, many sources that quote Kepler's laws of planetary motion. This is preventing me from finding out what I really want to know: which is - what are Kepler's laws as he wrote them? As opposed to how they may have been later interpreted.

Very specifically I am interested in whether "Kepler's First Law", as proposed by Kepler, which is usually stated in the form that orbiting objects in the solar system execute elliptical orbits with the Sun at one focus, actually recognised, or had a caveat, that in a 2-body system it is the barycentre that is at the focus of an ellipse for both bodies, and that it is even more complex in the case of 3-bodies or more.

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    $\begingroup$ Google 'kepler manuscript' or 'kepler manuscript transcription' and start from there? $\endgroup$ – user1569 Oct 17 '18 at 9:12
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    $\begingroup$ @CarlWitthoft History questions are still on-topic on Astronomy; incidentally, I think an astronomer is more likely to be able to interpret Kepler's writings in the way Rob wants it than a historian. Plus, astronomy questions on HSM are pretty rare, and I think the odds of it getting answered are much higher if it stays here. $\endgroup$ – HDE 226868 Oct 17 '18 at 22:30
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    $\begingroup$ This might help. Scroll down to the "Kepler's proof" part, which goes into the Math he used. You might be smart enough to deduce whether a barycenter is part of that proof or not. My hunch is he didn't work out barycenters because his work was observation to model, and his astronomia nova, while brilliant and world-changing at the time, is strewn with errors. If a PhD student today handed in something like Kepler's work, he wouldn't graduate . . . but I digress. math.berkeley.edu/~robin/Kepler/index.html $\endgroup$ – userLTK Oct 18 '18 at 9:13
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    $\begingroup$ I'll add this as well, Newton's comment on Kepler's ellipses, bottom of page 8: "Newton himself, for instance, considers that Kepler had “guessed” the elliptical form of the orbit: “......Kepler knew ye Orb to be not circular but oval & guest it to be elliptical......”: from: arxiv.org/ftp/physics/papers/0107/0107009.pdf source of quote: H. W. Turnbull (ed.): The correspondence of Isaac Newton, II, Cambridge, 1960, pp. 436-437 $\endgroup$ – userLTK Oct 18 '18 at 9:20
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    $\begingroup$ Here's a link to a translation of "Astronomia Nova", one of Kepler's main works: greenlion.com/books/astronomianova.html. You could try browsing its content; however, it won't have all his laws in there. He developed them over time. You'd have to find English translations for his other major works, and then find his exact wording. Here's an out-of-print translation of another one of this works: tinyurl.com/y7yqnh5c. $\endgroup$ – Alphecca Oct 18 '18 at 19:44

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