Every year, our Moon drifts about 1.5 inches farther from Earth. This quiet, almost invisible migration is slowly lengthening our days — a subtle reminder that our planet’s relationship with its satellite is anything but static.
For billions of years, Earth and the Moon have been locked in a gravitational dance that constantly reshapes both bodies. As the Moon gradually retreats, it’s not only slowing Earth’s rotation but also altering the tides and the rhythm of our oceans.
The gravitational tug-of-war behind the Moon’s drift
The Moon was born roughly 4.5 billion years ago, after a colossal collision between young Earth and a Mars-sized object. The impact hurled debris into orbit, which eventually coalesced into our satellite — once far closer than it is today.
In those early eons, the Moon loomed enormous in the night sky, pulling at Earth with tremendous force. Its gravity whipped up titanic tides and dramatically affected our planet’s spin.
The cause of its gradual retreat lies in those same tides. The Moon’s pull creates two bulges in Earth’s oceans that slightly lead its position in orbit because our planet spins faster than the Moon revolves. That offset acts like a cosmic brake — tugging the Moon forward, giving it energy, and pushing it outward into a higher orbit. At the same time, Earth’s own rotation slows down, making our days ever so slightly longer.
The Moon is slowly moving away from Earth, and this phenomenon is causing the days on Earth to lengthen. © Kyoshino, iStock
Proof written in light and stone
NASA scientists have confirmed this slow-motion drift using laser reflectors left on the lunar surface by the Apollo missions. By bouncing laser beams off them and timing the reflections, they’ve measured the Moon’s retreat at exactly 3.8 centimeters per year — accurate to the millimeter.
Ancient seashells tell the same story. A 2020 study in Paleoceanography and Paleoclimatology examined growth rings in 70-million-year-old Cretaceous mollusks. Like tree rings, these patterns revealed that Earth once had 372 days in a year — meaning each day lasted just 23.5 hours during the age of the dinosaurs.
Together, the evidence is clear:
• When the Moon was closer, Earth’s days were shorter.
• As the Moon drifts away, our rotation slows.
• Each inch of distance adds a fraction of a second to the day.
• This process has continued steadily for billions of years.
What the future holds for Earth and its Moon
If this gravitational waltz continued indefinitely, Earth would eventually become tidally locked — spinning once for every lunar orbit, always showing the same face to its companion. The tides would vanish, replaced by nearly still seas.
But that future will never come. About a billion years from now, the Sun’s growing radiation will boil away Earth’s oceans, silencing the tides and halting the Moon’s outward drift.
Long before that, we’ll see smaller, subtler changes. Total solar eclipses will become rarer and less complete as the Moon appears smaller in the sky. We’ll also notice weaker tides, changing the way our planet’s waters move and breathe.
In several billion years, the Sun will swell into a red giant, eventually engulfing both Earth and its faithful satellite — bringing this ancient cosmic partnership to its end.
This slow but relentless evolution is a humbling reminder that even the most stable systems in our universe are in constant motion, reshaping the world beneath our feet.
