Mars’s models behind Kepler’s ephemerides of 1604 and 1605

Abstract

This paper analyzes Kepler’s ephemerides for 1604 and 1605, along with related documentation, in light of his evolving models for Mars. Drawing on known manuscripts,we present and examine Kepler’s calculations for both ephemerides—calculationsthat, although preserved in previously identified sources, have not yet been studiedby scholars. By reconstructing these computations and analyzing the tables used assources, we demonstrate that both ephemerides were based on a metopoid model,similar to the one described in chapter 46 of the Astronomia Nova. We also show thatone of the tables used for the 1605 ephemeris contains a second table built under themodel proposed in chapter 48. This case study captures a key moment in Kepler’ssearch for a physically grounded planetary theory, just before the final formulation ofthe Astronomia Nova.