Episodes From the Early History of Astronomy

Before streets were brightly illuminated at night, astronomy was accessible to everyone and was a matter of great importance: for divination; for setting appropriate dates for planting, harvest, and festivals; for regulating lives. Phenomena in the heavens are still of great importance to many, and much of the lore of astronomy and astrology dates back to the earliest days of civilization. The astronomy of the ancients is thus of interest not only as history but also as the basis for much of what is known or believed about the heavens today. Because phenomena in the heavens are less familiar today than in earlier eras, this book begins with a brief description of what one can see in the sky on dark nights with the naked eye. It then turns to the astronomy of the Babylonians, who named many of our constellations, who are responsible for many of the fundamental insights of early astronomy, and who married mathematics to astronomy to make it an exact science. A chapter on Greek astronomy discusses various models of planetary motion, showing that the cycles and epicycles used by the Greeks have their modern counterparts in the computations used to compute the ephemeredes listed in the Nautical Almanac. The book then turns to a detailed discussion of Ptolemy's cosmology, the first to include quantitative models in an integral way. Though the Ptolemaic system is now often dismissed as unsound and inefficient, it is in fact a logically pleasing structure which, for more than a millennium, provided a framework for educated people throughout the Christian and Moslem worlds to think about the universe. Finally, after a brief review of the geometry of the ellipse, the author gives an elementary derivation of Kepler's equation, and shows how Kepler solved it, and further proves that a planet moves very nearly uniformly around the empty focus of its orbit. Thus an eccentric circular orbit with the empty "focus" as the equant point gives a good approximation to Kepler motions. The result of combining two such motions is then shown to be close to Ptolemy's planetary model. This book provides a fascinating look at the night sky and the techniques that early civilizations, particularly Babylonian and Greek, used to model planetary motions¿Aaboe does a masterful job of covering a wide array of intriguing topics in a relatively short book, and any effort expended on reading it will be well rewarded¿ talented students at the high school age and college students who are interested in these topics would likely find this book very enjoyable and enriching¿Overall, the book is fascinating to read for several reasons, including its observational astronomical viewpoint, its rich historical and cultural content, and, of course, its exposition and explanation of ancient techniques of celestial predictions and modeling. ?MAA ONLINE