The Moon is slowly drifting away from Earth at the same speed your fingernails grow.

We know exactly how fast the Moon is moving because of mirrors left on its surface. In 1969, Apollo 11 astronauts Neil Armstrong and Buzz Aldrin placed a special reflector on the Moon. Later missions like Apollo 14 and 15 left more. Scientists at places like the McDonald Observatory in Texas fire lasers at these mirrors and time how long the light takes to bounce back. This lets them measure the distance to the Moon with incredible accuracy.The reason the Moon is leaving us is all about energy. As Earth spins, the gravity from the Moon pulls on our oceans, creating tidal bulges. Because Earth rotates very fast, these water bulges actually sit slightly ahead of the Moon. This extra mass of water pulls the Moon forward, giving it a little boost of energy. This boost acts like a cosmic slingshot, pushing the Moon into a higher path around our planet.As the Moon gains energy, Earth loses it. This causes our planet to spin a tiny bit slower every year. Scientists studying ancient rocks found that 1.4 billion years ago, a day on Earth was only 18 hours long because the Moon was much closer. Back then, the Moon was likely only 14,000 miles (22,500 kilometers) away. Today, it sits about 238,855 miles (384,400 kilometers) from us.If this kept happening forever, the Moon would eventually take 47 days to go around Earth once. Our days would also become 47 days long to match. However, this won't happen for billions of years. Scientists believe the Sun will change and grow much larger before the Moon ever gets that far away. For now, we just get slightly longer days and a slightly more distant neighbor in the sky.