“Follow the evidence where it leads.”

• Kepler abandoned his much-loved theory of Platonic solids because it could not be made to fit Tycho’s observations.

• Kepler spent two years calculating Mar’s orbit according to the Ptolemaic system, using an equant. He got the model to match the data to within the limits of the precision of Tycho’s instruments, but he was not satisfied.

• He then developed two separate proofs that orbits are ellipses that have one focus at the center of the sun (First Law of Planetary motion). He didn’t like his conclusion the first time around--ellipses seemed to be “imperfect.”

• After starting from scratch and inventing a new method of interpreting the data, he came to the same conclusion.