Earth Is Slowing Down: Scientists Track the Spin—Will Days Ever Reach 25 Hours?

Earth is slowly stretching out its days from about 24 hours toward 25 hours because the Moon is gently tugging on our planet to slow it down.

Imagine you are spinning on a playground merry-go-round. If someone grabs your hand and pulls backward as you spin, you start to turn more slowly. The Moon does exactly this to Earth. It creates a giant ocean tide that drags against Earth's surface like sand under bare feet, acting as a brake for our planet's rotation. This process is called tidal braking.

Every day, the Moon’s gravity pulls on Earth's oceans, creating high tides. Because Earth spins faster than the Moon orbits, these tidal bulges get dragged slightly ahead of the Moon. The Moon pulls back on this bulge, slowing Earth down very little bit every year. Just like a spinning top eventually wobbles and stops, our planet is gradually losing speed. We are gaining about 1.7 milliseconds per century in day length. It seems tiny, but over millions of years, it adds up significantly.

In the distant future, yes, Earth’s days will stretch to 25 hours and eventually match the Moon's orbit perfectly. This is called a tidal lock. When that happens, one side of Earth will always face the Moon, just like the Moon already shows us only one side from our view here on Earth. The change won't happen overnight, so you won't notice your bedtime changing tomorrow morning. But in hundreds of millions of years, sunrises and sunsets will feel much longer to everyone living here.