Steven, first thanks for you rare input. I have two questions. First, though I think I know it, could you please explain in laymans terms what you mean by dynamic equivalence. secondly you said. The second is where the Earth does rotate, but is situated at the centre of the universe. This model is actually a special instance of the acentric model where one has simply just assumed that the Earth is at the centre, and therefore the sun must orbit the Earth once a year. I cannot understand what you infer here. If the earth rotates then why would the sun also orbit the earth annually. It seems that both movements would either be additive or subtractive. Maybe it was a ploy to get round the Geostationary satellite. I tried it once as an explanation, but it contradicts the bible... so I backed away. Philip.