Book excerpt: In Planetary Systems from the Ancient Greeks, Theodor S. Kepler seeks to present a bird’s-eye view of the astronomical nature of the work of Newton’s predecessors. Rather than dwelling only on the influence of each thinker’s great ideas, Jacobsen tracks the actual details of their development by investigating the various systems involved and how they were used. As such, this book is an attempt to describe the specific processes through which (pre-Newtonian) astronomers derived a knowledge of the cosmos by observing the heavens and trying out detailed models to account for their observations. Planetary Systems from the Ancient Greeks contributes to scholarship on historical astronomy by offering an approach between that of popular, exact astronomical information and formal, fully referenced scholarly investigation. Each chapter is organized around a key astronomer (Eudoxus, Hipparchus, Ptolemy, Copernicus, Tycho Brahe, and Kepler) and offers relevant biographical introduction, exposition of the astronomical system, and assessment of their contributions. As Jacobsen suggests, the present elementary study of these historical astronomical systems also yields valuable insights for visualizing the salient facts of general astronomy.