The Great Ptolemaic Smackdown

Oct 20, 2023
via akkartik

A 10-part blog series that describes the transition from Ptolemaic models of the universe to geocentric models, but comes from the perspective that there were lots of intelligent people who had lots of sensible reasons to avoid the geocentric models.

t’s not enough for a new model to equal the standard model in predicting phenomena; it must do better.  Otherwise, why bother changing?  And the Copernican model did not do that.  Nor were its calculations simpler.  To preserve pure Platonic circles, Copernicus used twice as many epicycles as Peuerbach’s then-current edition of Ptolemy!  That's right: epicycles.  The Earth revolved around the Sun on two circles; the Moon ran on an unprecedented double epicycle, and Mercury librated idiosyncratically across the center of an epicycle!  Try explaining that with a theory of universal gravitation!

I'm not very far into it but it's quite entertaining.

Kepler worked Mars in the Ptolemaic, Copernican, and Tychonic models, and none of them gave a good account.  He then assumed (as Copernicus had not) that all orbital planes passed through the Sun, which reduced the error to eight or nine arc minutes.  Still not good enough.  He even tried re-introducing the @#$%^; equants, though his heart wasn’t in it.

A Neoplatonic mystic, Kepler was convinced that physics must reduce to simple mathematical forms, but he was more liberal than either Copernicus or Galileo.  He began to try ovals.

...Without Tycho’s precise new data, Kepler would never have found his ellipse.  No one before Tycho could possibly have done so.  The old tables were just too badly corrupted. The interesting corollary to this is that as soon as it was possible to do so, European astronomers discovered elliptical orbits.

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