Days on Earth are getting longer as the Moon gradually moves away from our planet, new research shows.
Scientists have discovered that as the Moon moves further away, its changing gravitational impact on Earth is slowing the planet’s rotation and making the days longer.
They predicted that days on our planet might eventually reach 25 hours in length, but noted that would take about 200 million years.
The Moon is slowly moving away from our planet, causing Earth’s days to become longer and longer.
“As the Moon moves away, Earth is like a figure skater, spinning and slowing down as he stretches out his arms,” explained geoscientist Stephen Meyers, a professor at the University of Wisconsin-Madison.
The Moon is located about 238,000 miles from our planet and takes approximately 27.3 days to complete a single orbit around the Earth.
But previous research found that the Moon is moving away at a rate of about 1.5 inches per year, meaning it will take longer to move around our planet.
At some point, the Moon will reach a stable distance and will only be visible from one side of our planet.
For their study, Meyers and his colleague reconstructed the deep history of the Earth’s relationship with the Moon.
They discovered that 1.4 billion years ago, a day on Earth lasted only about 18 hours.
To make this calculation, the researchers invented a statistical method that links astronomical theory with geological observation to analyze the Earth’s geological past.
This allowed them to reconstruct a deep history of the solar system.
Earth’s days were shorter billions of years ago, largely because the Moon was closer to our planet.
This caused our planet’s rotation to spin faster than today, the researchers concluded.
But throughout Earth’s history, the Moon has been moving further and further away, in a process known as “lunar recession.”
We know this thanks to astronauts on the Apollo missions, who placed reflectors on the Moon that allowed scientists on Earth to shoot lasers toward the lunar surface and measure exactly how fast the Moon is retreating.
As the Moon gradually moves away, the Earth’s rotation slows down. The reason for this has to do with the Moon’s impact on ocean tides.
As the Earth spins, the gravity of the orbiting Moon pulls on the oceans, creating high and low tides.
The Moon’s gravitational pull causes ocean water to “bulge” toward it on the side of Earth that is closest to it.
At the same time, inertia tries to keep the water in place, but the Moon’s gravity is stronger, so the water bulges toward the Moon.
Meanwhile, on the opposite side of the Earth, the Moon’s gravitational pull is weaker simply because it is farther away.
As the Moon orbits the Earth, its gravity pulls on the ocean, causing bulges to form around the Earth’s core. This is partly what is causing the Earth’s rotation to slow down.
There, inertia is stronger than the Moon’s gravity and the water tries to continue in a straight line, which causes it to move away from the Moon.
The combined force of the Moon’s gravity and inertia creates two tidal bulges that remain aligned with the Moon as the Earth rotates.
But the Earth spins on its axis much faster than the Moon’s orbit, meaning that friction from the ocean basins moving beneath it also drags water along.
The bulges then move slightly ahead of the Moon’s orbit, which tries to push them back.
This gradually slows the Earth’s rotation while the Moon gains energy, causing it to move into a higher orbit.
Other factors also influence the Earth’s rotation, including climate change.
As global temperatures rise, polar ice is melting faster than ever, pouring water into Earth’s oceans.
All that meltwater gradually moves from Earth’s poles toward the equator, where the ocean bulges toward and away from the moon.
This has caused the Earth to grow even larger at its center, thereby slowing its rotation even further.
All of this means that Earth’s days are getting longer. The changes are so small that we won’t really notice them and they won’t affect our circadian rhythms.
But over millions of years, those small changes will add up to add an extra hour to Earth’s diurnal cycle.