The dozens of epicycles aren’t on a par with Kepler’s laws. “Planets move in circles plus epicycles” is what you have to compare with Kepler’s laws. “Such-and-such a planet moves in such-and-such a circle plus such-and-such epicycles” is parallel not to Kepler’s laws themselves but to “Such-and-such a planet moves in such-and-such an ellipse, apart from such-and-such further corrections”. If some epicycles are needed in the first case, but no corrections in the second, then Kepler wins. If you need to add corrections to the Keplerian model, either might come out ahead.
(Why would you need corrections in the Keplerian model? Inaccurate observations. Gravitational influences of one planet on another—this is how Neptune was discovered.)
I have heard that Copernican astronomy (circles centred on the sun, plus corrections) ended up needing more epicycles than Ptolemaic (circles centred on the earth, plus corrections) for reasons I don’t know. I think Kepler’s system needed much less correction, but don’t know the details.
Not for Kepler who lived about a century before Newton.
My question was about the Copernicus—Kepler debates and Newtonian mechanics were quite unknown at that point.
Even Kepler’s theory expressed as his three separate laws is much simpler than a theory with dozens of epicycle.
The dozens of epicycles aren’t on a par with Kepler’s laws. “Planets move in circles plus epicycles” is what you have to compare with Kepler’s laws. “Such-and-such a planet moves in such-and-such a circle plus such-and-such epicycles” is parallel not to Kepler’s laws themselves but to “Such-and-such a planet moves in such-and-such an ellipse, apart from such-and-such further corrections”. If some epicycles are needed in the first case, but no corrections in the second, then Kepler wins. If you need to add corrections to the Keplerian model, either might come out ahead.
(Why would you need corrections in the Keplerian model? Inaccurate observations. Gravitational influences of one planet on another—this is how Neptune was discovered.)
I have heard that Copernican astronomy (circles centred on the sun, plus corrections) ended up needing more epicycles than Ptolemaic (circles centred on the earth, plus corrections) for reasons I don’t know. I think Kepler’s system needed much less correction, but don’t know the details.