Moon Is Slowly Drifting Away

This cosmic dance is powered by a gravitational tug-of-war between Earth and its satellite. The Moon's gravity pulls on our oceans, creating a tidal bulge. Because Earth rotates much faster than the Moon orbits, this bulge is dragged slightly ahead of the Moon's position in the sky. The gravitational pull from this leading bulge of water then acts like a subtle slingshot, constantly accelerating the Moon and nudging it into a higher, more distant orbit. This transfer of energy isn't free; it comes at the expense of our planet's own rotational speed, causing Earth's day to lengthen by a minuscule amount over time.

Scientists can track this gradual separation with astonishing precision thanks to retroreflectors placed on the lunar surface during the Apollo missions. By firing powerful lasers from Earth and measuring the round-trip travel time of the light, they can pinpoint the Moon's distance to within millimeters. While the annual drift is imperceptible in our lifetimes, its long-term consequences are profound. Today, we experience total solar eclipses due to the remarkable coincidence that the Moon and Sun appear the same size in our sky. In about 600 million years, however, the Moon will have receded so far that its apparent size will be too small to completely obscure the Sun, forever ending the spectacle of totality for future Earth-dwellers.