MargenEvery year, the Moon drifts about 3.8 centimetres farther from Earth: roughly the rate your fingernails grow.
We know this with astonishing precision thanks to the mirrors the Apollo missions left on the lunar dust. For half a century, observatories have fired laser beams at those reflectors and timed the bounce: the exact distance, measured with light.
The tides are to blame. As it spins, the Earth drags its bulge of water a little ahead of the Moon, and that displaced mass tugs at it like a leash, speeding it up and pushing it into an ever-higher orbit. In exchange, our days grow longer, ever so slightly: when the dinosaurs walked the planet, a day lasted about 23 hours.
Nothing in the sky stands still. Not even the Moon of all the songs.
Source: NASA