“Over the past decade, the average length of day has mostly been shrinking. This has been especially notable over the past five years or so, sometimes clocking in at less than 24 hours,” says Nicholas Stamatakos, an astronomer at the U.S. Naval Observatory’s Earth Orientation Department.

Here’s the science behind why Earth is spinning faster as it orbits the sun, if scientists think it will last, and why even the odd millisecond might impact critical technologies.

Why is Earth spinning faster?

Variations of Earth’s rotation are due to a complicated mix of factors but scientists say a few stand out.

The moon affects Earth differently during its orbit. When it’s positioned close to the equator twice a month, gravitational pull slows Earth’s spin a bit. But the moon also moves nearer the poles twice a month, and at those times the moon’s gravity helps Earth spin a bit faster.

Our planet and atmosphere rotate in sync, sharing a momentum that can’t be changed by only one of the two. Our atmosphere spins more slowly during the summer due to variations in the jet stream. This means the planet must speed up, to compensate and maintain the system’s angular momentum at a constant level.