A E L Davis (Imperial College, London, UK); Chair: T J Mahoney

Two professional historians will present accounts of what astronomy was like in Kepler's time (1571-1630). In his day most people still believed that the universe (the solar system) was geocentric, and Kepler set out one of his most cogent arguments for heliocentricity by describing what astronomy would have been like if viewed from a satellite (a word he invented) - that is, from the Moon. Thus one of the talks will discuss Kepler's lunar astronomy; the other will explain how Kepler's laws were discovered. Using only the straightedge and compasses permitted by Euclid, Kepler was able to construct an unknown curve to fit the observations, and finally to give exact geometrical proofs that that curve was an ellipse, and that time was measured by area.

Posters contributed by student, or young graduate, historians of astronomy will be most welcome.