Our moon is slowly ditching Earth

The Moon appears slightly smaller in the sky each year as it drifts further away. It drifts 3.8 centimeters further away from Earth annually, roughly the same rate your fingernails grow.

This celestial breakup is caused by tidal friction. As the Moon's gravity pulls on Earth's oceans, it creates a bulge of water that actually sits slightly ahead of the Moon's position. This bulge tugs the Moon forward, giving it a boost of energy that slingshots it into a higher, wider orbit.

Energy is a zero-sum game in physics. Because the Moon is gaining energy to move away, Earth is losing it. Our planet's rotation slows down by about two milliseconds every century to pay for the Moon's travel.

Go back 620 million years, and an Earth day lasted only 21 hours. Eventually, the Moon will move so far away that it will no longer appear large enough in the sky to fully block the sun, making total solar eclipses physically impossible.

In billions of years, the Earth and Moon could theoretically become tidally locked, though the Sun will likely expand and end the system before that happens.