Robert B. re your post - From Robert Bennett Wed Apr 04 03:59:20 2007. I think at last I see where the problem lies! All this time I've been assuming you were arguing from a scientific position, in particular that your definition of orbital period would be the same as the definition used by the rest of the scientific community, ie one orbit is one 360 deg revolution by a satellite about its primary, not the time between successive appearances above a fixed zenith. This allows the same definition of an orbital period to be used for any satellite regardless of whether either it or its primary is rotating or not and if so, in what direction. It's so much simpler if we only need one universal rule. Added to this is the fact that with an immobile Earth, the two are synonomous. First may I ask whether you agree or dissagree with this assessment? Next, may I ask whether you believe that the orbital period of a satellite, as understood by the wider community, for constant seperation, is affected or is not affected by the direction of its revolution, and if it is, in what manner? Paul D Send instant messages to your online friends http://au.messenger.yahoo.com