Tycho, Longomontanus, and Kepler on Ptolemy’s Solar Observations and Theory, Precession of the Equinoxes, and Obliquity of the Ecliptic

Abstract

It is well known that there are errors in Ptolemy’s observations of the Sun with consequences for his own astronomy and for later astronomy up to some time in the seventeenth century. The principal problems and their consequences in Ptolemy’s astronomy are the following:

It therefore remains that either Ptolemy committed fraud with fabricated observations, or from a kind of awe and reverence for the ancients preferred to confirm rather than refute them, neither of which is likely in the philosopher Ptolemy, a defender of candor and truth, as is witnessed by many judgments, especially since he could expect no advantage or fame from this, but rather greater advantage and fame from correcting the ancients. But that he was not obsequious to the ancients, he left witnessed in many ways, refuting Hipparchus where it was required.

Johannes Kepler (1937–, 21.1.324).