We don't all think the earth isn't the centre of the universe just because Copernicus said so. That's the point. It's not authority, it's all repeatable experiments and confirmable logic. Science. Not faith. Regards, Mike. Quite true. But all these confirming experiments are done within the paramaters of the first concept. Quite naturally they will fit and be repeatable. Prior to copernicus all the calculations also confirmed the earlier view and were repeatable. (locally) If you read my little story/example to Alan on the subject of absolute immobility as being a real concept, you should see that the alien right from the start had absolute faith that the larger stone was immobile and that the other one including himself (when he landed on it) was in orbit around the other stone. Of course every experiment he did within his paramaters of belief would prove him right. But as the author (creator?) of this test I can say with absolute certainty that he is wrong. He would have to jump the mental barrier of his perceptions, and say what if....and consider alternative possibility.... So then he might say "Orbital motion is acceleration. And go about detecting it. et al. What is my point? In this debate there are two faiths and within two different sets of parameters, using the same laws of motion in Newtonian physics, both of which can be demonstrated to have merit. I dispense with special relativity simply because it is a mathmatical concept which proposes certain physical properties to exist according to his theory of relativity, when such physical properties may also exist under a different reality, there being a real aether for example. These equations according to my opinion are fed with what I would call "probability factors". These worry me, because whereas we were previously able to safely talk of doppler shift in terms of an aether, by arbitarily for no reason other than it not being detected by Michelson, they dismissed the aether, it became necessary to throw in a new probability and name it the relativistic doppler. etc. They appear, even if it is not the intention, to keep seeking a proof of their previous belief, by making more numerous and complicated theories and calculations whenever their observations go against them. At this stage from the purely scientific angle I am neutral. I want a real experiment that can safely show one way or the other. Alans aberration so far doesn't work for me.But ....has anyone thought of this or has relativistic doppler made it irrelevant? For the sake of this experiment I am assuming the heliocentrical earth orbiting the sun. Take a star that has a known stable light spectrum and is equally visible from two positions 180 degrees apart on the earth orbit. As far as I can know, perhaps the speed is not sufficient, but would a red shift on the away movement of the earth be detectable against a blue shift on the up side 180 degrees 6 months later? Just an idea. I look forward to someone saying light doppler does not work with a moving observer.??? Philip.