A Day on Earth Is Getting Longer

The silent dance between the Earth and Moon is subtly reshaping our experience of time. The Moon’s gravity pulls on our planet's oceans, creating tidal bulges on opposite sides of the globe. As Earth spins, it drags these bulges of water slightly ahead of the Moon in its orbit. The Moon’s gravity, in turn, pulls back on this displaced mass, creating a braking effect known as tidal friction. This gentle but relentless force has been slowing Earth's rotation for billions of years, acting like a cosmic brake.

This transfer of energy has two major consequences. First, it lengthens our day, though the change is imperceptible in a human lifetime. The effect accumulates dramatically over geological time, which is why ancient corals from 400 million years ago show that a year contained around 400 shorter days. Second, as the Earth loses rotational energy, that energy is