Son brought this book home from his sophomore year at St. John’s College in Santa Fe. You know the school has its bona fide’s when their faculty have written, edited and published the definitive modern editions of these classic books.
This was a fun read. I started with Ptolemy, and the geocentric worldview he championed about 40 CE, and followed some of the geometry proofs (having studied Euclid too many years ago). I watched him build his ‘epicycles’ (circles upon circles) to explain the progression and retrograde motions of the 5 visible planets.
Retrograde: here’s a bonus term for those of us no longer into astrology: it is the apparent reversal of the motion of planets gradually migrating across the sky. From the newspaper, I recall reading statements like ‘Mars is retrograde in Capricorn’ and thinking ‘what hocus pocus is this?!’ Now I know that it means Mars is migrating in reverse direction and it is positioned inside the constellation of Capricorn in the sky. It makes a little more sense descriptively, but I still don’t buy that astrology foretells my future as a result.
Clearly, says Ptolemy, the only rational view of the heavens are that they are concentric spheres. The proof is that with his excellent math, he can predict the positions of the stars into the future.
1400 years later, Copernicus thinks deeply and has an insight (how, though, did he have that insight?). I love books, like Lavoisier’s on Chemistry, where the author lays out his stepwise experiments and failures, and gradual reasoning toward the invention of the concepts of oxygen and hydrogen…
Nevertheless, Copernicus lays out the groundbreaking and heretical thought that the Earth is not the center, and that the sun is the ‘center of the world.’ Heliocentrism. He has to tread gently, as he is shattering what has been accepted by scholars (and the Church) for over one thousand years. (What do WE accept that has been true for 1000 years?)
In his introduction Copernicus gingerly states that both he and Ptolemy have explanatory systems that predict planetary motion successfully. But, the heliocentric model is SO MUCH SIMPLER.
So, how to explain why Mercury and Venus have a much smaller range as they move across the sky night after night, and Mars, Jupiter and Saturn seem instead to span the entire sky? Ptolemy has to jump thru hoops and invent weird epicycles to make sense of this, and yet Copernicus sweeps away all that complexity by saying Earth is itself a planet with an orbit BETWEEN Venus and Mars. Thus the ‘inner planets’ behave differently from the ‘outer planets’ based on Earths own orbit and ‘overtaking’ the orbits of those outer planets. And all the epicycles fall away. It is one of the most ‘ohhh’ beautiful moments in the history of science.
Devastatingly, he draws out what Ptolemy’s epicycles requires planets to do (spirographic pirouettes through space, ridiculous when you look at it that way).
Cool read, even if this aging person is too lazy to revisit Euclid and plow through the math. The thinking, the paradigm shifting, the worldview challenging. That’s fun. Next up, Kepler and Galileo.