re "different DYNAMICS of launching something to rendezvous with the Moon " Philip, I hope I am right in this assessment of your current position? However, the whole issue gets clouded over all too easily by APPEARANCES. To sort this out, we MUST understand that the only reason a heliocentric system is said to be equivalent to a geocentric system DYNAMICALLY, is if the World rotates in BOTH of them. Do you follow? Neville. I agree absolutel;y!.. Re the "dynamics", and the "appearances" ....Understanding it completely though is not easy. I have difficulty with "appearances" for example in working out in my mind which way the moon is really moving in the heliocentric model.. I have no such problem with the geocentric model... Given a pen and paper I realised I had the moon going the wrong way in my post, yet none "got me" for it. I cannot even begin to imagine the gyrations if the earth was spinning, but NOT orbiting the Sun annually. Philip