The Dance of the Moon

A book that attempts to explain the motion of the moon—a phenomenon that has baffled astronomers for quite some time.

In this work, Spolter (Gravitational Force of the Sun, 1994) delves into lunar movement. As she points out in her preface, this book isn’t full of mathematical equations or theories; instead, it presents “easy to understand graphs based on the latest ephemerides of unprecedented accuracy.” The motion of the moon is a problem that has attracted many of the great astronomical and mathematical minds over the centuries. Sir Isaac Newton himself couldn’t explain it, and the 18th century Swiss mathematician and physicist Leonard Euler abandoned his own work on it. The problem is so incredibly difficult because it’s a “three-body” problem; that is, it involves the sun and the earth as well, which makes it mathematically complex from the start. Furthermore, any proposed theories can be easily compared with real-world observations, making errors immediately apparent. However, Spolter here has tools that no one before the modern era could have imagined. Atomic clocks play a key role, for example, as does lunar laser-ranging technique, as well as specialized software. Drawing on her own previously published research, Spolter provides readers with a series of graphs measuring the moon’s periods, its perturbation by the sun, the eclipse cycle, and the “obliquity of the ecliptic,” among other lunar phenomena. Readers need not have advanced degrees in math or astronomy to understand it, but Spolter’s analysis does demand one’s full attention, and at least a high degree of familiarity with mathematical concepts and symbols. Those who don’t have these skills may not fully appreciate the author’s work. That said, readers who are familiar with the overall problem, and with the means that the author uses to solve it, will find it very intriguing indeed.

A complex collection of lunar data that invites interpretation and consideration.