But I didn't think of them. I have been rereading the Sherlock Holmes stories and thought of Watson's amazement at the detective's nescience in the matter.
My surprise reached a climax, however, when I found incidentally that he was ignorant of the Copernican Theory and the composition of the Solar System. That any civilized being in the nineteenth century should not be aware that the earth traveled around the sun appeared to me to be such an extraordinary fact that I could hardly realize it.In that bit of dialogue Arthur Conan Doyle touches on the continuing points of the discussion. First, educated people are just supposed to know this. Notice he doesn't mention how they are supposed to know this, nor does anyone getting worked up over the 25% of Americans when it comes up these days. The truth is, there are very few people who can demonstrate it by observation. The math and the record-keeping alone eliminates most people. (In a cloudy area like Seattle, people might never find it.) The sun continues to look as if it goes around the earth, and we continue to say that the sun rises and sets. A lot of us could illustrate it - heck, my second son did something similar for his 2nd-grade science fair when he put up a refrigerator box and invited people inside to show how the phases of the moon worked. Flashlight and tennis ball, I think. (It was cool.) A few could put forth a convincing argument that the retrograde movement of some planets, which has been known for many centuries, suggests that while they do orbit, they are not orbiting the earth, suggesting that they at least orbit the sun, and so too us. But that's not a proof, and the idea of retrograde movement of Mars is also something that 99% of us know only because we read it somewhere.
"You appear to be astonished," he said, smiling at my expression of surprise. "Now that I do know it I shall do my best to forget it."
"To forget it!"
"You see," he explained, "I consider that a man's brain originally is like a little empty attic, and you have to stock it with such furniture as you choose. A fool takes in all the lumber of every sort that he comes across, so that the knowledge which might be useful to him gets crowded out, or at best is jumbled up with a lot of other things, so that he has a difficulty laying his hands on it. Now the skillful workman is very careful indeed as to what he takes into his brain-attic. He will have nothing but the tools which may help him in doing his work, but of those he has a large assortment, and all in the most perfect order. Depend upon it there comes a time when for every addition of knowledge you forget something that you knew before. It is of the highest importance, therefore, not to have useless facts elbowing out the useful ones."
"But the Solar System!" I protested.
"What the deuce is it to me?" he interrupted impatiently; "you say that we go around the sun. If we went around the moon it would not make a pennyworth of difference to me or my work."(A Study In Scarlet)
So educated people have this told to them, usually pretty early on and repeated in a variety of contexts, so it really should be embedded by the time you get out of highschool even if you aren't studying much science. Thus it is true that we should be as surprised as Watson when someone doesn't know it. But it is largely a measure of believing your teachers and the people one reads, not any personal scientific merit on our own part. Because of the partly-correct story about Galileo, there is also some association that if people don't believe it, it must be because some nefarious religious people have suppressed the idea. In the absence of any known Christian school or home-school curriculum that actually teaches a Ptolemaic universe, it's not very, uh, scientific for people to come to that conclusion. But it fits the prejudices, as above, so the data matters* little.
A more likely conclusion is that 25% of the population wasn't paying very close attention in school and doesn't read much, and are thus unreliable sources for many types of information, not just astronomy.
Secondly, Doyle recognises through Holmes that the information doesn't directly change life for most of us. I don't use the information in either work or hobby. Farmers, foragers, and fishermen knew enough about the seasons to keep the rest of us alive without having a heliocentric theory of the universe. We are affected indirectly by the technology developed by people who did need to know it, but even that is not so thoroughgoing as one would think. Even most of the sciences don't rely much on knowledge of the solar system.
The long hard struggle of learning to reason uses math and science as one of its key classrooms. Thus we rather automatically assume that people who don't know much science must not be able to reason very well. You will find that to be true in your everyday experience, of course, because we try to educate children with some general knowledge of many things. If they don't know basic science, then basic history and geography may also have passed them by. But science and math aren't the only classrooms, and reasoning can be taught without very much of those. Nearly all of the science of Aristotle or Plato has been overturned, but their reputations for reasoning remains solid.
*Yes, I know that many of you think that should be "data matter" instead, and until a very few years ago I would have agreed with you and gone back and changed it after typing it. I am on the other side of that divide now. I have a reasonably good command of my native language. What sounds correct to me is by definition, correct. Were I writing or speaking in some formal setting I might change it so as not to be a distraction to the audience. But the change might be even more of a distraction.