I like these two contributions by Allen and Philip, and suggest that we reply to them on a point by point basis, with no more than 2 points per posting. Otherwise some are going to be bogged down with huge, and difficult to comprehend, e-mails. Allen - I reject your claim that the distance to the Sun and Moon can be obtained by simple triangulation, using two points on the surface of the World as a baseline. This is untrue because of the atmosphere, which refracts incoming light towards the normal. I.e., the atmosphere makes things outside it seem further away (at any angle except zenith). The "accepted" amount of refraction is based upon the assumed distance to these objects and is therefore another instance of circular reasoning. Neville. Send instant messages to your online friends http://uk.messenger.yahoo.com