After all its closeness and pull, the final truth is this: the Moon is slowly moving away from Earth.

The change is subtle—about an inch and a half each year—but relentless over deep time. The Moon’s orbit is widening. Earth’s days are lengthening. The system is still adjusting, four and a half billion years after it began.

We know this with unusual precision. During the Apollo missions, astronauts left small arrays of mirrors on the Moon’s surface. From Earth, scientists fire laser pulses at them and time the return. That steady two-and-a-half-second round trip, measured year after year, shows the distance increasing by millimeters, confirmation that the Moon’s retreat is real and ongoing.

It comes down to friction—oceanic, relentless, barely perceptible. The Moon raises tides in Earth’s oceans and flexes the planet itself. As those tides move, friction steals a trace of Earth’s rotational energy. That energy doesn’t disappear. It migrates outward, nudging the Moon into a slightly higher orbit. Earth slows. The Moon recedes. A slow trade, endlessly repeated.

There was a time when the relationship was far more intense.

Models of the very early Earth suggest a day once lasted only five hours. The Moon loomed enormous—dozens of times wider in the sky—circling overhead in a matter of hours, driving tides so strong they sloshed across the planet. Days were quick. Nights brief. The world itself was in motion. Over billions of years, that relentless pull traded Earth’s spin for the Moon’s distance, stretching the day and retuning life’s clocks.

The Moon still rises on schedule. It looks unchanged. Familiar. But it is farther away than it once was—by a margin too small to notice, and too steady to halt.

In roughly 600 million years, the geometry will finally fail. The Moon will be too small in the sky to cover the Sun completely. Every eclipse after that will be annular—a ring of fire where darkness used to be. Total solar eclipses, the kind that stop traffic and make grown adults weep, will be gone forever.