Moon Drifting Away: The Slow Recession Explained
Science has confirmed a long-persisting drift: the Moon is gradually moving farther from Earth. The rate is about 1.5 inches (3.8 cm) per year, a tiny but measurable change that has intrigued scientists for decades. The figures come from Lunar Laser Ranging (LLR) experiments that bounce laser pulses off corner-cube reflectors left on the Moon by Apollo astronauts and later missions, then measure the return trip with extreme precision. Over years of data, these pulses reveal how the Moon’s distance from Earth shifts—and how fast that shift is happening.
How scientists measure the drift
LLR works by firing a laser from Earth toward retroreflectors placed on the Moon’s surface. When the light hits these mirrors, it bounces straight back to Earth. By timing the round trip with extraordinary accuracy, researchers calculate the Moon’s distance to millimeters over time. This method has remained reliable since the Apollo era and continues to be refined with modern instrumentation. In short, photons travel to the Moon and back, and every photon adds a data point to our understanding of the Earth–Moon system.
As reported by The Conversation and highlighted by WION, these measurements are complemented by models of lunar orbit and Earth’s gravity field. The result is a robust picture of a slowly receding Moon that has altered the dynamics of our planet for billions of years and will continue to do so for billions more.
Why the Moon is getting farther
The core reason is tidal forces. The Moon’s gravity creates two tidal bulges on Earth: one on the side facing the Moon and one on the opposite side. Because Earth spins, these bulges are not perfectly aligned with the Moon’s position. The rotation drags the bulges slightly ahead, and the gravitational pull of these forward-shifted bulges exerts a net forward tug on the Moon, boosting its orbital energy. In effect, energy is transferred from Earth’s rotation to the Moon’s orbit, causing the Moon to speed up a little and drift outward. Simultaneously, Earth’s rotation slows down ever so slightly, lengthening our day by a small amount each century.
Monthly variations and long-term trends
It’s important to note that the Moon’s orbit is not a perfect circle. Its distance from Earth varies by roughly 20,000 km (about 12,400 miles) over the course of each orbit. When the Moon is at perigee (closest approach) the distance is shorter; at apogee (farthest point) it’s longer. This monthly fluctuation can lead to brighter or larger-looking full Moons on occasion, commonly referred to as “supermoons.” The long-term, average recession, however, is the steadily increasing distance that results from tidal energy transfer, superimposed on these regular orbital changes.
What it means for Earth and Moon
Though the rate—about 3.8 cm per year—is small, it is a fundamental aspect of the Earth–Moon relationship. Over long timescales, the shifting distance influences tides, the locking of rotational dynamics, and the stability of orbital interactions. For now, the drift is a natural, measurable consequence of gravitational physics: a reminder of how interconnected our planet is with its natural satellite. It’s not a sign of danger; rather, it provides valuable data for understanding planetary formation, tidal dynamics, and celestial mechanics.
Sources and credibility
For background on lunar recession and its measurement, scientists cite Lunar Laser Ranging data and analyses published in venues like The Conversation, with coverage and context provided by WION as a preferred source. NASA and partner institutes continue to monitor the Earth–Moon system to refine models and confirm the long-term trend.
