The History and Practice of Ancient Astronomy

This is an extremely useful book; by far the most user-friendly guide to ancient astronomy available. Both the technical and historical aspects are generally presented with admirable clarity. My only complaint is that the early chapters on pre-Ptolemaic ideas are too cursorily treated. Unlike the thorough discussion of Ptolemy's system and the outline of Copernicus' system, this early material is presented in recipe-book form with little emphasis on ideas. Consider for example the theory of the gnomon. Much time is spent discussing gnomon plots (i.e. plots of the shadow cast by a vertical stick in the course of a day) and their practical uses. But our curiosity is suppressed: looking at a sequence of gnomon plots over the course of a year (p. 54) one naturally wonders why the curves are hyperbolas, except the equinoxes where the curve is straight. Not even the latter is explained. This is very unfortunate because it would have paid off greatly to think about these interesting and natural questions at this stage, since the answers lead naturally to several ideas developed subsequently. Let's see how. Why hyperbolas? Because the sun moves in a circle, thus generating a cone with the tip of the gnomon as vertex; drawing the gnomon plot amounts to cutting this cone with a plane, so one gets a conic section. Why straight at the equinoxes? Because then the daily orbit of the sun contains the tip of the gnomon in its interior; drawing the gnomon plot amounts to cutting this plane with a plane, so one gets a line. These simple insights are very fruitful. They immediately suggest Ptolemy's equatorial ring (p. 206), for example. And they would have helped us greatly in the construction of the sundial (pp. 133-139), a very complicated construction which Evans pulls out of a hat in pure cookbook form. If we had taken the time to think about the gnomon plot earlier we could now have approached this construction much more naturally as follows. To create a sundial means putting hour marks on our gnomon plot. To do this we should divide the sun's daily orbit into 24 equal parts and figure out how to find the corresponding points on the plot. This is easiest at the equinoxes, since the orbit and the tip of the gnomon are then coplanar, as we saw. By contrast Evans goes straight for the much more complicated cases of the solstices, and then obtains the marks for the equinoxes as a by-product. This construction would have been natural instead of artificial if one had understood the equinox construction first, just as later the solar theory (being simple but having the essential ideas) is a good introduction to the planetary theory, as Evan emphasises. In fact, if we were willing to settle for an approximate sundial we could have avoided Evans complicated construction altogether by extrapolating the hour curves from equinox line by qualitative reasoning as follows. Since the sun's position at a given hour throughout the year are all coplanar, the hour curves on the

Upon receipt of this book, I just read it from cover to cover. It's easily one of the most interesting and illuminating astronomy books that I own. James Evans explains very clearly how ancient astronomers obtained such a vast amount of data with very simple instruments.

This is great book. I got to take the class for which the book was the class book, and the author was the professor. Class time was used for discussing the history and practice of the ancient astronomers from the babylonians to copernicus. We then were able to take a lab time to go through the well written excerisize to actually do the astronomy as, say, the ancient greeks did it. You can learn how the ancient greeks were able to predict the position of the stars and planets using the principle that the earth is the center of the universe. I took the class 2 years ago, and every once and awhile i pull out the book just to read through or make a new astrolobe plate.

The big problem when writing a book about history of science, is how much background to include. If you don't include any background, the ordinary reader will not really get what's going on. Evans has instead written what can best be described as a two-fold book. It's both an introduction to astronomy and an introduction to history of astronomy! His explanations, and particularly his illustrations, are excellent. Both his scholarship and his writing are exceptional! Read it!

An impressive compendium of thousands of years of astronomy--from Babylon to Copernicus. In tracing the history of star-gazing, Evans traces the history of science, showing how ideas arose, migrated, stood up or failed under testing, and were passed down through the centuries. One learns a deep respect for ancient astronomers. Almost 2,000 years before Columbus, Greek scientists had figured out that the world was round, and had even determined that the Earth was miniscule compared to the size of the universe. Evans is committed to the idea of learning by doing, so he gives detailed instructions on how to construct every instrument that ancient astronomers used--from sundials to astrolabes. The book is full of great science projects. I would strongly recommend this book for those interested in the history of science, ancient and medieval thought, backyard astronomy... even astrologers would benefit greatly from this book.