The role of ephemerides from Ptolemy to Kepler

Owen Gingerich

pp. 17-24

in: Elisa Felicitas Arias, Ludwig Combrinck, Pavel Gabor, Catherine Hohenkerk (eds), The science of time 2016, Berlin, Springer, 2017

Abstract

Celestial timekeeping relied in the first instance on the movements of the stars and planets. The principal systematic positions of planets are recorded in ephemerides, which are primarily predictions, not observations. Prior to the invention of printing, ephemerides are extremely rare, which gives lie to the widespread mythology that astronomers before the days of printing were eagerly observing the heavens to add epicycles to improve the accuracy of the tables.