The science blogging community has been having a good laugh over the past few days about a “scientific” conference being held in South Bend Indiana (near Notre Dame!) on how Galileo was wrong about the heliocentric solar system. Yup, it’s a conference to discuss and review the science and politics of the geocentric model supporting the idea that the Earth is at the center of the solar system.
Along with the expected jabs at the whole notion, a study showing that only 79% of Americans believe the Earth travels around the Sun is often cited. Comments about this usually range from simple ridicule of public knowledge to condemnation of science education in the country. Others say the blame shouldn’t be placed on education but on religious institutions instead. I’ll stick with blaming education.
Bear with me as a make a statement that will, at first, seem as if I’m part of the ignorant 21% of America. Geocentrism (the hypothesis that the Sun and all the planets revolve around the Earth) should not necessarily be ridiculed out of hand as a completely silly notion. When standing on the Earth making observations of the universe it does an amazing job explaining what you can see and measure using simple instruments. It is a good scientific theory in that it uses those measurements to construct a hypothetical model of how the solar system works and makes testable predictions which can be observed.
“But what about retrograde motion of the outer planets?” you may ask. Excellent question! Your class participation is duly noted. We can see that, from the perspective of the Earth, at times some planets appear to stop in their orbit of the Earth, move backwards for a bit, then proceed forward once again. Geocentrism can explain that by placing those planets in their own, smaller orbit about a point which itself orbits the Earth. Back when geocentrism was the accepted theory of how the solar system worked, scientific predictions were made and the future observations were very accurate. The heliocentrics of the day also tried to explain such motion, but their predictions were less accurate. Science, rightly so, considered the Sun-centered model to be wrong. Geocentrism fit the data better and made better predictions.
Here in Chicago the Adler Planetarium has an amazing display of mechanical models of the solar system. I recall seeing one showing just how an Earth-centered solar system works. If you are ever in Chicago it’s worth taking a look at the collection.
The Sun-entered model made such bad predictions because planetary orbits are not circular. Once Kepler developed the theory that planets swept their orbits out in ellipses rather than circles supporters of the now-altered Sun-centered model were able to make predictions just as accurate as supporters of the Earth-centered model. The two theories now had equal evidence to support them. Some hung onto the Earth-centered model since it was better established. Others preferred the Sun-centered model for its simplicity.
There were developments, though, that tipped the balance in favor of the Sun-centered solar system. Ethan Siegel over at Starts With a Bang! explains why and compares the two competing theories. To summarize, the invention of the telescope allowed for new observations. First it was noticed that Jupiter had its own set of moons which obviously orbited Jupiter and not Earth. While this observation discredited the religious notion that everything in the universe revolved around our planet, it was not the nail in the coffin of geocentrism. After all, the outer planets already were thought to revolve around their own central point in an epicycle. Imagining that moons could orbit planets while those systems orbited the Earth was not difficult.
What was difficult to explain, though, was the telescopic observation that Venus had phases and that the phases coincided with an apparent increase or decrease in observed size of the planet. That observation was repeated by independent astronomers again and again. No geocentrist was able to come up with a plausible, testable model to explain the observation. The heliocentric model, on the other hand, actually predicted such an observation. Science finally had the final nail to drive into the geocentric coffin.
The scientific theory that the earth was at the center of the solar system was still a good theory. You could use the scientific method to make predictions and test those predictions. It was rightly accepted as the best model until previously unavailable observations were made. It was rightly discarded once a different theory better fit the observations while still making good testable predictions. A geocentric solar system model wasn’t silly. It was good science. It just happened to be wrong.
The Sun is at the center of our solar system with the Earth and other 7 planets revolving about it in nearly perfect ellipses. One in five Americans do not know this. I blame our education system. For an explanation of why you will need to stay tuned to this channel.