Last week, a biology professor at the college where I teach called my attention to something strange in a recent New Yorker piece.
The story, A Very Rare Book, was a riveting tale about a forged copy of Galileo’s Starry Messenger, sold as a special one-of-a-kind “proof.” It’s worth reading for the access the writer got to the mind and motives of the alleged forger. There was only one real paragraph of science – the story’s lead – and that was where the oddity occurred:
On the night of January 7, 1610, Galileo Galilei, a resident of Padua, walked onto his balcony and tipped his telescope toward space. He spotted three stars near Jupiter and graphed their positions in a notebook. Six days later, he looked through his telescope again and found the same stars—but their positions had shifted. They were, he realized, moons orbiting Jupiter. Galileo had long believed Copernicus’ theory that the Earth was not the center of the universe. Now he had proof.
How would the discovery of Jupiter’s moons prove Earth moves around the sun? Why would having moons of its own prove Jupiter didn’t orbit Earth? It sounds very esoteric. The connection is a head-scratcher and at odds with what I’d learned in a wonderful book called The Copernican Revolution by Thomas Kuhn. The book was published before the philosopher’s more famous book, The Structure of Scientific Revolution, and the Copernican book is an easier read.
My professor friend teaches a humanities/science course that includes Starry Messenger. In his view, the problem is that Galileo’s observations of Jupiter’s moons don’t prove Copernicus right (Most scientists don’t really think in terms of proof), but it falsified the Aristotelian cosmology underlying the earlier Ptolemaic model. Having the Earth at the center was only part of that system. The Aristotelian picture also held that Earth was corrupt and everything in the heavens was pure and perfect, and that all heavenly bodies moved around the Earth. Bodies orbiting Jupiter violated the rules.
This more complicated story made sense.
Starry Messenger included other observations that were devastating to the Aristotelian picture. There were the mountains on the moon and the phases of Venus. My memory of Kuhn’s book wove many different observations and lines of thinking into what he called the Copernican Revolution. Crucial were Kepler’s elliptical orbits. With circular orbits, according to Kuhn, the Copernican model wasn’t much more predictive than the Ptolemaic one.
A quick check back to Wikipedia says that among Galileo’s observations, it was not the moons of Jupiter but the phases of Venus that proved most important in backing Copernicus, but the connection there is not obvious either and requires a little explanation for it to make sense.
A Very Rare Book is still a great story and the science here is peripheral to the plot. But the author missed an opportunity to explain how Starry Messenger changed the world. Adding another couple of sentences would have made it a lot simpler.
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