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Monday, March 26, 2007

Owen Gingerich on Copernicus

Owen Gingerich has written The Book Nobody Read: Chasing the Revolutions of Nicolas Copernicus. New York: Walker & Company, 2004. The title comes from Arthur Koestler's book, The Sleepwalkers, which was a popular book about early astronomy. According to Gingerich, Koestler claimed that nobody, or at least no important astronomers, read Copernicus' work, De revolutionibus (On the Revolutions of the Heavenly Spheres, 1543). Gingerich found most, or all, of the existing copies, and shows, from evidence such as annotations in the books by important astronomers, such as Kepler, that Koestler's claim was false. Gingerich is a professor of astronomy and the history of astronomy.

He writes: Today we admire Copernicus for having the audacity to introduce the heliocentric cosmology into Western culture, essentially triggering the Scientific Revolution. The Copernican cosmology did not just provide the modern blueprint for the solar system. It was a compelling unification of the disparate elements of the heavenly spheres. The greatest of scientists have been unifiers, men who found connections that had never before been perceived. Isaac Newton destroyed the dichotomy between celestial and terrestrial motions, forging a common set of laws that applied to the Earth and sky alike. James Clerk Maxwell connected electricity and magnetism, and showed that light was electromagnetic radiation. Charles Darwin envisioned how all living organisms were related through common descent. Albert Einstein tore asunder the separation between matter and energy, linking them through his famous E = mc2 equation.
Copernicus, too, was nothing if not a unifier. In the Ptolemaic astronomy each planet was a separate entity. True, they could be stacked one after another, producing a system of sorts, but their motions were each independent. The result, Copernicus wrote, was like a monster composed of spare parts, a head from here, the feet from there, the arms from yet another creature. Each planet in Ptolemy's system had a main circle and a subsidiary circle, the so-called epicycle. Mars with its epicycle was a prototype for each of the other planets, but because the frequency and size of the retrograde was different for each planet, an epicycle with an individual size and period was required for each planet. Copernicus discovered that he could eliminate one circle from each set by combining them all into a unified system. Owen Gingerich, The Book Nobody Read: Chasing the Revolutions of Nicolas Copernicus. New York: Walker & Company, 2004. pp. 53-4.


He presents evidence that ". . . neither Copernicus nor his predecessors were interested in adding extra circles just to make the predictions work a little better. Nevertheless, the legend of epicycles on epicycles has become so pervasive that barely a year passes without some author in the Physical Review or the Astronomical Journal remarking, apologetically, 'Maybe my theory has too many epicycles.'" Clearly, I haven't stamped out the myth. pp. 59-60.

And writes about Kepler:
In the Ptolemaic system, the Sun moved around its circle at a constant speed -- it just looked as if it moved at different speeds because it wasn't at the center of the Earth's circle.

And this, Kepler believed, had to be wrong. If Mercury, the planet closest to the Sun, moved fastest, and Saturn, the most distant planet, moved slowest, then this was because Mercury, being closer, soaked up more of the Sun's motive power and thus naturally moved faster. But in winter the Earth wasn't closer to the Sun than in summer, and Kepler reasoned that it should actually be going faster in its orbit in winter. That was physics, and Kepler, as the world's first astro-physicist, worked out the consequences. p. 168.

Thanks for reading.

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