Selections from Kepler's Astronomia Nova (Science Classics Module for Humanities Studies)

I so enjoyed this book! It was wonderful to read the greatest work of Johannes Kepler in his own words. I found his writing earnest, defiant, strikingly informal, down-to-earth, and brilliant. The selected excerpts from Astronomia Nova are a terrific way to understand Kepler's accomplishments -- with lots of helpful and thoughtful annotations by translator William Donahue. Lots of detailed geometry and diagrams, for those who are interested.From Socrates to Ptolemy to Islamic astronomers to Copernicus to Brahe, circular planetary orbits were held sacrosanct for over a millennium. Using the observational data of Tycho Brahe and his own ingenious geometric models, Kepler showed they were all wrong: planetary orbits are elliptical. In this translation of his book, we see Kepler's thought processes, ingenious geometric constructs, and persistence.Kepler was devoutly religious and a fiercely independent thinker. In this book, we see his arguments against taking biblical passages too literally. And we see his courageous defense of the Sun-centered solar system of Copernicus: " . . . while in theology it is authority that carries the most weight, in philosophy (physical science) it is reason . . . the Inquisition nowadays is pious, which . . . denies (earth's) motion. To me, however, the truth is more pious still . . "Even though Kepler's magnetic, spinning Sun as the source of planetary motion is wrong, it is still a milestone in science. Here was the first attempt (as far as I know) to explain the physical cause behind the motions of planets -- presaging the work of Isaac Newton.And we get to read about it all -- his assertions and his doubts -- from Kepler himself. What a privilege.

I love using this as one of my required texts for the History and Philosophy of Science course I teach. It's great at introducing Kepler's work to first time readers and it also has primary sections from his work. What's best is that you can guide your students through these prime selections without having to lose them in mathematics. And if you are so inclined, and it's worth the try, there are some problems you can tackle and you only need a limited amount of geometry.I also recommend it if you're just into the history of science.

Bought this book for my husband who teaches astronomy and physics. He says it has given him great insight into the roots of what he now teaches.

I truly wish I could return this. It might be a quarter of inch thick with 14-pt font. I did not know I was only buying "selections" and truly wish I could re-do and buy the complete Kepler work. Do not buy this.

"My aim in the present work is chiefly to reform astronomical theory ... so that what we compute from the tables may correspond to the celestial phenomena. ... Meanwhile, although I place this goal first and pursue it cheerfully, I also ... inquire into celestial physics and the natural causes of the motions. ... Indeed, all things are so interconnected, involved, and intertwined with one another that after trying many different approaches to the reform of astronomical calculations ... none other could succeed than the one founded upon the motions physical causes themselves, which I establish in this work." (Introduction, pp. 4-5).A decisive step towards this new physical theory is Kepler's proof in chapter 24 that the earth requires an equant, i.e. that the point with respect to which it moves uniformly is not the center of the orbital circle but rather a point close to it. The old theory, without the equant, had worked well for Ptolemy (sun instead of the earth, of course) and Copernicus, since it predicts the angular position very accurately. But Kepler shows that it fails to predict the distance between the earth and the sun. This distance at different times can be determined by observing the sun and Mars at times 687 days apart; this is the period of Mars, so we get a simple trigonometric calculation with both Mars and the sun as fixed points.Thus the earth now has an equant just as the outer planets did for Ptolemy and Copernicus. "Further, there is nothing to prevent our believing the same of Venus and Mercury. Indeed, I now have a proof that this is the origin of the belief that the centers of these planets' eccentrics move around on a small annual circle. Therefore all planets have this [eccentric circle with an equant]." (Chapter 32, p. 52).So the equant is no longer just some trick but in fact a universal principle, so we feel that it must have a deeper explanation. The key observation is that the equant (with bisected eccentricity) makes the planet's speed inversely proportional to its distance from the sun (chapter 32). This suggests that "the power that moves the planets resides in the body of the sun" (chapter 33).Kepler thinks we should pretty much have seen this coming, considering the "worthiness of eminence of the sun" and the fact that "the source of the world's life ... is the same as the source of the light which forms the adornment of the entire machine, and which is also the source of the heat by which everything grows" (pp. 57-58). Indeed, the motive power's "very close kinship with light" is confirmed by its linear deterioration with distance, since it spreads over the circumference of a circle so to speak (p. 59). Of course one might argue that since light, and perhaps also the motive power, spreads in three dimensions, i.e. over the surface of a sphere, it should obey an inverse square law, but Kepler has already made up his mind on the linear law---"And this is true, both of the steelyard or lever, and of the motion of the planets: that the weakening of power is in the ratio of the distances" (p. 56)---so we stick to two dimensions and conclude that "in all respects and in all its attributes, the motive power from the sun coincides with light ... although this light of the sun cannot be the moving power itself" (p. 59).The motive power instead appears to be of a magnetic nature. "The magnet, however, does not attract with all its parts, but has ... fibers ... extended throughout its length, so that if a little piece of iron is placed in a middle position between the heads of the magnet ... the magnet does not attract it but only directs it parallel to its own fibers. Thus it is credible that there is in the sun no force whatever attracting the planets ... but only a directing force, and consequently that it has circular fibers all set up in the same direction" (chapter 34, p. 69).But what about the equants? This makes them look artificial and silly. Kepler has the answer: equants are nothing but a pale manifestation of a deeper principle, the law of equal areas (chapter 40). Ok, so equants are out. Now what about the orbits? Actually, circular orbits will have to be abandoned altogether, as Kepler proves in the case of Mars in chapter 44, essentially by switching the roles of Mars and the earth in the argument of chapter 24 above. Donahue notes:"Interestingly, Kepler's working notes show that when he first made this comparison, he was sure there must be some error and made a note that he must give some thought to how to adjust the planetary positions to make the orbit circular. Several weeks later, when he was comparing the area law with an equant-based theory, he realised that his physical theory demanded an oval orbit. Only then did he trust the observational evidence!" (p. 85).Ok, so now orbits are ellipses ("ovals"). But what physical principles could possibly explain that? How does the planet know in which direction to turn and at what speed to go if the orbit is so elaborate? "So then, Kepler, would you give each of the planets a pair of eyes? By no means, nor is this necessary, no more than that they need feet or wings in order to move." (sic, chapter 39, p. 75). The magnet analogy suggests a solution. The sun's motive power creates a circular stream, but the planets don't quite follow this stream because they themselves are "magnetic"---this is how the earth can make the moon move---and this interferes with the stream as if the planet held a slowly turning oar in the stream: sometimes it agrees with the stream, sometimes it counteracts it. Kepler does not intend to build a quantitative theory on these grounds, but only to illustrate that the phenomena can be explained by basic physical principles: "I will be satisfied if this magnetic example demonstrates the general possibility of the proposed mechanism." (chapter 57, p. 94).

This is an excellent introduction to Kepler for people not confident in their ability to breeze through the more complex mathematical arguments of his "celestial physics." Kepler's own introduction is enough to enthrall any reader of history/philosophy of science. Anyone with some background in geometry and ancient astronomy will see that he is a stunning mathematician. Even for this edition of selections, I advise having some familiarity with Euclid and Ptolemy. General familiarity (from Wikipedia, even) of Copernicus and Brahe would be very helpful to understand what he's arguing against. I suppose it would be possible to pick this up and read it without any of this other stuff, but I personally would've been lost without the undergirding of first year-and-a-half of the mathematics program at St. John's College.After reading this I quickly put Kepler at the top of my "Must Read More" list. The editors and translator are very helpful and accommodating.I recommend this to any mathematics/physics-lover looking for a first-hand introduction to Kepler's world.

The editor's background material is not really enough for grasping Kepler's mathematical points (the selection is "for Humanities Studies"), but we get enough to enjoy his style of reasoning -- and polemic. It is still common for the preface of a scientific book to give advice to readers, on how to connect mentally with new material, but Kepler gives separate "Advice to astronomers" and "Advice to Idiots", which would well be taken by today's creationists.

Difficult to read but altered my perception on everything