Philip M I'm sorry Philip, I got preoccupied going through your post checking the numbers and my mind wandered when I got close to the end. I hadn't arrived at understanding just what it was you were trying to show. Correct me if I haven't figured it out yet -- you're not directly concerned with the speed the Moon is moving, only its contribution to determining whether the Earth is moving. If this is so, then is it your purpose to show that a beam of light -- fixed in space -- will paint a band of light on the Moon's surface as it sweeps by at 1. 30 km/s +/- 1 km/s (depending on which side of its orbit it is on) if the Earth is moving or 2. 27 km/s if the Earth is not moving; and that this can be determined from the length of the band? Firstly, I must agree with Robert B that you'll need an awfully powerful laser. However, if you were to adapt my strategy of measuring the angle of lead for a hit on the LRRR, I don't see why this is not feasible. Of course you would need to conduct the experiment at full moon or new moon rather than half moon to maximise the effect. But you have only a 3 km/s +/- 1 km/s difference -- not a lot to play with. The difference in angle of lead is then a minimum of 298 u deg and a maximum of 596 u deg. This is less than A. Centauri's parallax. If however you take a two stage approach to the problem, you may be able to improve your chances. There are four possibilities - Earth moves at 30 km/s Moon moves at 1 km/s Earth moves at 30 km/s Moon moves at 27 km/s Earth moves at 0 km/s Moon moves at 1 km/s Earth moves at 0 km/s Moon moves at 27 km/s First, measure whether the Moon is crossing the Earth's orbit at 1 km/s or 27 km/s. This has two possibilitie outcomes - Earth moves at 30 km/s Moon moves at 1 km/s (T) (1) Earth moves at 30 km/s Moon moves at 27 km/s (F) (2) Earth moves at 0 km/s Moon moves at 1 km/s (T) (3) Earth moves at 0 km/s Moon moves at 27 km/s (F) (4) or- Earth moves at 30 km/s Moon moves at 1 km/s (F) (5) Earth moves at 30 km/s Moon moves at 27 km/s (T) (6) Earth moves at 0 km/s Moon moves at 1 km/s (F) (7) Earth moves at 0 km/s Moon moves at 27 km/s (T) (8) If the first set is found, then repeat the tests at new and full moon. We need to determine whether the required angle of lead is atan ( 30+/-1 / 384 400 ) or - atan ( 1 / 384 400 ) If the result is ~ 4.32 m deg or ~ 4.62 m deg then (1) is true. If the result is ~ 149 u deg then (3) is true. If the second set is found, again repeat the tests at new and full moon. We need to determine whether the required angle of lead is atan ( 30+/-27 / 384 400 ) or - atan ( 27 / 384 400 ) If the result is ~ 8.5 m deg or 447 u deg then (6) is true If the result is ~4.0 m deg then (8) is true. Some of these possibilities are easier to differentiate than others. (6) when velocities add would stand out as would (3) neither of which fit either the helio or geo(static) models. The two favoured models are the closest together. What a shame. Oh! Well it was fun thinking about it. Paul D ____________________________________________________________________________________ Yahoo!7 Mail has just got even bigger and better with unlimited storage on all webmail accounts. http://au.docs.yahoo.com/mail/unlimitedstorage.html