Galileo still has many folks bamboozled. The narrative persists more than four centuries after he trained his telescope on Jupiter that Galileo’s discovery of the giant planet’s moons proved, despite the dogmatic objections of the church, that Copernicus was right about the sun being at the center of the solar system.
Dennis Danielson says much of that common narrative is false. Danielson is a professor of English at the University of British Columbia. Milton is his professional bailiwick, but he’s got a strong interest in rhetoric and the history of science, which has led him to publish a couple of books on astronomy and astronomers. He’s the editor of The Book of the Cosmos (Basic Books, 2002) and wrote The First Copernican (Walker & Company, 2006). It was during his work on the latter, about Georg Joachim Rheticus, the young German mathematician who was largely responsible for getting Copernicus’s De revolutionibus published, that Danielson developed what he calls a “perfectly discreet, I assure you, love affair with Copernicus.”
Danielson spoke Thursday at the University of Washington astronomy colloquium, and later that evening at a meeting of the Boeing Employees Astronomical Society. He said that in addition to Galileo’s obvious genius in many areas, he was a top-notch public relations practitioner, a successful propagandist, and a bit of a sneak.
Danielson said Galileo wasn’t telling the whole story with his masterwork Dialogue Concerning the Two Chief World Systems, the publication that supposedly confirmed Copernicus and got Galileo into hot water with the Vatican.
“I really do want to be respectful of Galileo, but he sewed some misinformation, starting right on the title page of his work, that I would propose to you has played into the twisted story of cosmology” and some longstanding misperceptions, Danielson said.
The catch, according to Danielson, is that the title page and the entire Diologo depict the scientific debate as one between the Copernican and Ptolemaic systems. In fact, Ptolemy’s system was well on its way out by the time the Dialogue was published in 1632, and the system drawn up by Tycho Brahe in 1588 was much favored by scientists for many decades to follow. The Copernican model was not really proven for some 200 years.
In fact Galileo’s own observation of the phases of Venus in 1610, 22 years before Dialogue, essentially knocked Ptolemy out of the cosmological playoffs.
“This was in fact striking another blow to the scientific underpinnings of the Ptolemaic system,” Danielson said, “but this demonstration supports Copernicanism only if there is no alternative other than Ptolemy.”
But Tycho’s system was an alternative that also correctly predicted the phases of Venus. Kepler with The Rudolphine Tables in 1627, Riccioli with Almagestum Novum in 1651, and Hooke with An Attempt to Prove the Motion of the Earth from Observations in 1674 all tended to favor the Tychonic system over Copernicus more than a century after “De Rev” and 42 years after Galileo’s Dialogue.
“If the Ptolemaic and Copernican systems truly were the only two great systems of the universe, then you could logically affirm the one by denying the other,” Danielson said. “But Galileo was wrong that those were the two great systems. Not in his day, not in Hooke’s. There was a third, the Tychonic system, which answered most of the criticisms of the other geocentric and geostatic systems without getting into all of those absurd claims about a moving Earth.”
There were other scientific challenges for proving Copernicus. They couldn’t detect parallax, as it turned out the observations were not yet precise enough. Some stars appeared as disks in telescopes, which turned out to be an illusion but argued against Copernicus at the time. Scientists expected to observe a Coriolis effect if Earth rotated, but Coriolis didn’t get around to finally seeing it until 1835.
“The physics that underpinned Copernicanism wasn’t fully developed until Newton,” Danielson said, “and the scientific impediments to a full-scale acceptance of Copernicanism were not removed until the 19th Century.”
Danielson gives Galileo credit for being right in the end.
“His book was powerful. He so firmly planted the idea that there was an A or a B, so established that way of thinking, it became easy for us to forget” that Tycho’s was long the preferred model until Newton came up with the physics that supported the Copernican model.