Hey, i've got a question which I hope you guys can help me with. It is observed that Mars is somewhat brighter when in opposition (ie. sun- earth - mars in that order) that at other times. How can this be explained using a) The Ptolemaic model and b) The Copernican model of the solar system. (Assume that Ptolomy's construction describes the actual motion of the planet) I know that at diffrent times of the year, mars appears brighter. I think it was a 2 yr cylce. It's 'cause Mars gets closer to earth at that time. "Opposition for Mars occurs about every two years, when Mars appears opposite the sun as seen from Earth. Now the planet rises in the east when the sun sets in the west and arcs across the sky -- a brilliant reddish light -- all night long. This happens, of course, around the time we on Earth are flying between Mars and the sun." But does anyone have any good explanations? I don't really understand this question either, if anyone can clarify it, it'd be great ! Thanks a lot !!