In addition to that, while Kepler was lecturing on the Great Conjunction he was drawing the trigon [1] which shows how the locations of Great Conjunctions change over time. This drawing (consisting of a triangle inscribed inside a circle that gets shifted over time), inspired him to pursue the idea that the distances to the planets were determined by polygons of different shapes inscribed in circles. This didn't work, so he moved on to Platonic solids, which worked better, but still not perfectly. Eventually this pursuit lead him to the idea of describing the planetary orbits by ellipses.

[1]: https://en.wikipedia.org/wiki/Great_conjunction#/media/File:...