The Moon Drifts 1.5 Inches Further From Earth Each Year

Right now, as you read this, the Moon is quietly sneaking away from us. Not dramatically—it's not ghosting us like a bad date—but at a measured pace of about 3.8 centimeters (1.5 inches) per year. That might not sound like much, but over millions of years, it adds up to a cosmic separation story.

We know this with remarkable precision thanks to the Lunar Laser Ranging Experiment. Astronauts from the Apollo missions left reflectors on the Moon's surface, and scientists on Earth bounce laser beams off them to measure the distance down to the millimeter. It's essentially playing catch with light across a quarter-million miles of space.

Why Is the Moon Leaving Us?

The culprit is tidal friction. Earth's gravity creates bulges in the Moon, and the Moon's gravity creates tides in Earth's oceans. As our planet rotates, these tidal bulges don't align perfectly with the Moon—they get dragged slightly ahead by Earth's spin.

This misalignment creates a gravitational tug that acts like a tiny rocket booster, gradually pushing the Moon into a higher orbit. Meanwhile, the Moon pulls back on Earth's tidal bulges, slowing down our planet's rotation. It's a cosmic exchange: Earth loses rotational energy, and the Moon gains orbital energy.

What Does This Mean for Earth?

As the Moon drifts away, Earth's days get longer. Currently, our days are increasing by about 1.8 milliseconds per century. That's imperceptible to us, but over deep time, it matters enormously.

About 1.4 billion years ago, when the Moon was closer, Earth's day lasted only 18 hours. Going further back to when the Moon first formed—roughly 4.5 billion years ago—it was about 10 times closer than today, and an Earth day lasted just 5 hours.

Will We Lose the Moon?

Not likely. The Moon won't drift away forever. Eventually, in about 50 billion years (if Earth and the Moon survive that long), the Moon's recession will stop. At that point, the same side of Earth will always face the Moon, just as the same side of the Moon always faces Earth today. They'll be tidally locked in a cosmic stare-down.

But don't worry—the Sun will engulf both Earth and Moon in about 5 billion years, long before that happens.

The Historical Detective Work

Scientists have confirmed this gradual separation by studying ancient coral fossils and tidal rhythmites (layered sedimentary rocks formed by tides). These natural timekeepers preserve records of day length and tidal patterns from hundreds of millions of years ago, providing physical evidence of the Moon's ancient proximity.

So yes, the Moon is leaving us—slowly, measurably, and inevitably. But at 1.5 inches per year, you've got time to appreciate those moonlit nights before it becomes a slightly smaller dot in the sky.