The Moon Is Slowly Running Away From Earth

Thanks to laser-reflecting mirrors left on the Moon's surface by the Apollo missions, scientists have been able to precisely measure its distance from Earth for decades.

The result: the Moon is drifting away at about 3.8 centimeters a year — a side effect of the same tidal friction that's slowing Earth's rotation.

The long-term consequence is dramatic: hundreds of millions of years from now, the Moon will be far enough away that its disc will no longer fully cover the Sun, and total solar eclipses will become impossible — only annular ones will remain.

For now, we're living through a lucky coincidence: the Moon happens to sit at just the right distance and size to look nearly identical in the sky to the far larger, but far more distant, Sun.