So I'm taking physics this semester, and our teacher for it's a pretty cool guy. Really smart, eccentric, rambles on and loses the plot, etc. Think he's going to be a great teacher.
Anyway, while driving home the point on the difference between rote memorization and actual learning, he asked us to name one thing, one thing that proves that the earth goes around the sun, and not the other way 'round. And he bet a free test grade weighted A than no one would have an answer.
Well, I got to thinking. First thing to mind was libration of the moon; but that only proves that the moon goes around the earth. Then I thought of all the astronauts and instruments we've sent into space; but that just proves that the earth is round. Then I got it. Parallax of the stars as the earth goes around the sun!
Ding ding, free A for me on first day of class. Apparently he usually gets just one or two people each semester (and he teaches ten classes a semester) who can provide a proof, and I was one of those this year.