“Is the Moon getting farther away from Earth?” – Judah, 9, Broken Arrow, Oklahoma
The Moon is indeed moving away from us at about 1.5 inches (3.8 centimeters) each year. Scientists find this out by bouncing lasers off special mirrors left on the Moon by astronauts. By timing how long it takes for light to travel to the Moon and back, they can measure the distance very accurately.
But the Moon’s distance isn’t constant. It changes throughout the month as it orbits the Earth. While it averages around 239,000 miles (385,000 kilometers) away, its path isn’t circular; it varies by about 12,400 miles (20,000 kilometers). That’s why some full moons appear extra large—these are called supermoons.
As an astrophysics researcher, I love studying how celestial objects interact. Tracking the Moon’s movement over billions of years helps us understand its and Earth’s evolution since they formed 4.5 billion years ago.
Tides and the Moon
So why is the Moon drifting away? It all ties back to tides. The Moon’s gravity pulls at the Earth, creating tides—bulges of water that shift as the Earth rotates. This pull is stronger on the side closest to the Moon and weaker on the opposite side, leading to two bulges. As the Earth spins, these bulges move, always trying to point at the Moon.
Interestingly, due to the Earth’s rotation, these water bulges don’t align perfectly with the Moon. Instead, they pull the Moon slightly ahead in its orbit, giving it an extra boost. Imagine a pitcher throwing a baseball—if they throw harder, the ball travels farther. This gravitational “tug” is why the Moon’s orbit is expanding over time.
Experts say that this gradual increase affects Earth too. As the Moon gains momentum, Earth’s rotation slows down, making days very slightly longer. But don’t worry, that change is minimal—just a tiny fraction of a percent each year. We’ll continue enjoying our familiar tides and eclipses for millions of years.
The Moon’s Past and Future
What about the Moon’s history? In the beginning, it was much closer to Earth—so close that it appeared larger in the sky. Fossil evidence shows that Earth’s days were shorter back then, roughly 23.5 hours about 70 million years ago when dinosaurs roamed the Earth.
Looking forward, will the Moon ever break free from Earth’s gravity? In a distant future, Earth could become tidally locked to the Moon, meaning we would only see one side. However, the Sun’s increasing brightness and eventual expansion will likely eliminate conditions needed for this to happen, likely destroying both the Earth and the Moon long before that.
The science of our Moon is fascinating! Though it’s gradually moving away, we can still marvel at its beauty during the night. Enjoy the tides, the eclipses, and all the wonders the Moon gifts us.
