Watching the constellations of stars move by every season and then return would pretty much tell anyone that the earth is moving a-round.<br /><br />Were the sun orbiting the earth, then the stars would not be moving except as the earth turns on its axis. Thus the full constellations would be seen every 24 hours. <br /><br />But on our earth the sun is in the way over half of the time and so those same constellations cannot be seen except seasonally. That argument was probably usable to argue that the earth did indeed orbit the sun.<br /><br />That it was missed by the ancients to refute Ptolemy, simply indicated that they had not throught the situation thru carefully enough, that is, they had a huge bias against thinking carefully enough. IE, the earth is the center of the universe and damm the evidence.