The observer's guide to planetary motion

de Dominic Ford

To the naked eye, the most evident defining feature of the planets is their motion across the night sky. It was this motion that allowed ancient civilizations to single them out as different from fixed stars. "The Observer's Guide to Planetary Motion" takes each planet and its moons (if it has them) in turn and describes how the geometry of the Solar System gives rise to its observed motions.Although the motions of the planets may be described as simple elliptical orbits around the Sun, we have to observe them from a particular vantage point: the Earth, which spins daily on its axis and circles around the Sun each year.