It's not obvious that the sun isn't spinning around the earth instead. You could use coordinate acceleration in an earth-centered frame and the sun would be spi

It's not obvious that the sun isn't spinning around the earth instead. You could use coordinate acceleration in an earth-centered frame and the sun would be spinning around the earth. That's equally as correct as the conventional view. So I think a test can be that if someone doesn't understand that the sun is spinning around the earth, then they probably don't actually understand at the earth is spinning around the sun - they just believe it. I'm a physics teacher, and most teenagers don't have a clue about this at all. They think astronauts float around in space because there's no gravity there. If there's no gravity, then how does the earth stay in orbit around the sun? That shows they really don't understand it at all. It's difficult and you have to actually think hard over a long time to make all the pieces fit together.