On the Revolutions of Heavenly Spheres

Copernicus puts the sun in the center of the universe. This is a great achievement not on metaphysical or philosophical grounds but rather because it provides new quantitative information about the universe, namely planetary distances. Suppose the earth is at the center and we have created a model for how the planets move with epicycles and stuff, as Ptolemy did. Such a model can give no information about planetary distances, because we could scale the orbit of Saturn, say, to make it twice as big and it would still look exactly the same seen from earth. But suppose now that we have a similar model but with the sun at the center, which is what Copernicus provides. The (relative) planetary distances are now determined, because if we scaled the orbit of Saturn then it would look the same seen from the sun but different seen from earth. So with the earth in the center we cannot determine planetary distances because we are the center of scaling, but with the sun in the center we would notice scaling and thus the planetary distances are locked, or, as Copernicus puts it, "this correlation binds together so closely the order and the magnitudes of all the planets and of their spheres or orbital circles and the heavens themselves that nothing can be shifted around in any part of them without disrupting the remaining parts and the universe as a whole". Thus he can claim triumphantly that earlier astronomers "have not been able to discover or to infer the chief point of all, i.e., the form of the world and the certain commensurability of its parts. But they are in exactly the same fix as someone taking from different places hands, feet, head, and the other limbs---shaped very beautifully but not with reference to one body and without correspondence to one another---so that such parts made up a monster rather than a man." (I'm using the translation from Goldoni's excellent article in the Mathematical Intelligencer.) Other benefits of the Copernican system include explanations of the following. Retrograde motion, including: retrogression coincides with opposition and maximum luminosity (for superior planets); retrogression is more frequent the further the planets is from us; the retrograde arc is greater the closer the planet is to us. Bounded elongation of inferior planets. Peculiarities of Ptolemy, including: Ptolemy's planets all have a solar component (viz., to explain bounded elongation or why retrogression coincides with opposition) but the moon does not; periods not constant as seen from the earth.

OK, first of all, "GangstaLawya" seems to not be taking into account the fine work of Kepler, Newton, and Einstein when he suggests that we "remain agnostic" on the issue of heliocentrism. True, Copernicus himself does not excactly refute Ptolemy here (he actually was more worried about how other astronomers and Protestant theologians would react to his heliocentric system than how the Catholic church would see it... and his model wasn't fully accepted until over a hundred years after his death), but this model was later augmented by Kepler and Newton to the point where it does work better than Ptolemy's. And with all due respect, the Ptolmaic system is extremely convoluted, needlessly complicated, and downright ugly at times... so even if there's a simpler way of looking at things that works just as well, that's still a conceptial improvement. Occam's razor, y'know? But I digress. As with most of my reviews of books like this, my concern isn't necessarily the actual book (which is usually self-evidently worthwhile), but with the presentation. I must say that it's a little awkward to see Stephen Hawking's name appear on the cover in larger type than Copernicus' and not get anything more than a very short introduction by him that doesn't say very much. In fact, there is not very much of a difference between this edition and the one published by Prometheus Books; the text is exactly the same and contains all the same diagrams. The cover is flashier (and says "Stephen Hawking!") and the type is cleaner. That's it. Those are the only real differences. In fact, the only reason I can see for this edition existing is Running Press (and Stephen Hawking) making a few bucks. Despite all this, there isn't really anything here that detracts from the work. So basically, you can buy this copy or the Prometheus Books edtion and it won't matter; you'll get pretty much the same thing and pay pretty much the same price either way. I'll leave it up to you whether you want the flashy cover (complete with Stephen Hawking's name on it) or the plain one because that's really about as deep as the choice goes.

Never before did I know a man could explain the heliocentric universe as well in this book. Of Course, Copernicus explained it centuries before my birth. But, it seems so foolish to believe the geocentric view, and I'm Catholic. Read "Dialogues" by Galileo to get the full picture of what these two men said, it it truly fascinating.