 | Dear Gramps, Does the earth rotate around the sun, or is it the other way around??? My physics teacher asked for a list of reasons why I believed one way or the other. I said that I believed our solar system was heliocentered, not geocentered, but I didn't have much luck in finding reasons to back up my belief. I looked in the encyclopedia, but it didn't recognize the word "helio", and I looked through several web pages about space programs and educational programs about our solar system, but none seemed to have the answer I was looking for. Can you help?? love, Ashley. |
Dear Ashley,
Let's see-- The sun is 93 million miles away, so the diameter of the earth's orbit-- or the sun's orbit--(whichever is moving) is 186 million miles. If you took a picture through a telescope of a given star field at one time, then again six months later, since you'd be shooting from two positions separated by 186 million miles The near stars, such as alpha centari, which is only 4.2 light years away, would show up on the photograph in a slightly different position against the background of more distant stars if the earth were rotating around the sun. This is called parallax. If the earth were stationary in the star system and the sun were rotating, then the star field in both photos would be the same. By the way, one of the dictionary definitions of parallax is -- the angular difference in direction of a celestial body as measured from two points on the earth's orbit.
Gramps.