
The Apollo astronauts left behind retroreflectors on the lunar surface that scientists still bounce lasers off today, and the round-trip time has been measured precisely enough to prove the Moon is drifting away from Earth at 3.8 centimeters per year, about the rate your fingernails grow.
Apollo astronauts left passive mirror arrays on the Moon in 1969, 1971 and 1971. Lasers fired at those reflectors from Earth now measure the lunar distance to within centimeters, and the data shows the Moon receding at 3.8 cm per year — about the pace your fingernails grow.














