What is the distance between the earth and the moon?
This is the average distance. among the objects left on the moon by Apollo astronauts was a small mirror. Scientists bounced a laser beam of light from the Earth off the small mirror. they then measured the time it took the beam to reflect back to the Earth. Since they knew the speed of light, they could judge the distance to the moon accurately.
Z = ct
Z = Distance to an Object
c = speed of light
t = time it takes for light to reach us (laser beam or reflected sun light).