[FlorinAndrei]

At some point you have to rely on "givens". You can't go turtles all the way down.

[JoeAltmaier]

Sure you can. Ham operators bounce a wave off the moon. Time the round trip. Speed of light. Or send a blip thru a spool of fibre optic cable, measure the transit time. It CAN be directly measured.

[sliverstorm]

So how did you figure out how far away the moon was?