On 07 Aug, Jack Lewis <jandj.lewis@xxxxxxxxxxxxx> wrote: > Dear Alan, How do we know that the radar ranging is accurate? I stuggle > to believe that radar can be used in this way. Oh come on! Radar has been in use since the 2nd world war! You send an incredibly high power radar pulse out, and it reflects back off the object you're looking at, and when it returns you see how long it has taken to do the double journey, and work it out by distance = speed x time. They do the same with laser beams to the moon, reflecting it off the reflector which the astronauts from Apollo 14 left on the moon for that purpose. They can measure the distance to the moon to within a millimetre! I'm told that there are some idiots who claim that man has never landed on the moon, and that all the photos were taken in a studio! Well the laser reflector proves conclusively that they did land, because it is used practically every week by astronomers. Alan Griffin