- No. 2Reading Five Pages Deeply: Swerdlow on Ptolemy's Solar Model, Checked Assertion by Assertion, with Two Misprints Found
Five pages of Noel Swerdlow's posthumous The Renaissance of Astronomy (2026) set out Ptolemy's solar model: the length of the year, the eccentric and the epicyclic form and their equivalence, the equation of centre, Ptolemy's derivation of the parameters from the seasons, and the later values of al-Battānī, az-Zarqāl and the …
Gerd Graßhoff · 10 November 2026 · version 1.0 · PDF, 11 pages - No. 1Reconstructing Kepler's Reasoning in the Astronomia Nova: A Compact Argument about the Equant, Made Explicit and Checked Step by Step
In chapter 4 of the first part of the Astronomia nova Kepler gives, in eight lines and one figure, the argument by which Copernicus charged Ptolemy's equant with making the heavens move unequally: about the centre of its circle the planet passes a lesser arc and a greater arc in equal times. We reconstruct this argument. First …
Gerd Graßhoff · 10 November 2026 · version 1.0 · PDF, 12 pages
Famulus Lettre is published by OpenScienceTechnology GmbH and edited by Gerd Graßhoff. Every issue is a Famulus Notebook: its sources, figures and reconstructions can be followed to their origin. An issue keeps its number and its address; a correction appears as a new version. The issues are published under the licence CC BY-NC-ND 4.0.
