Days are slowly getting longer as the Moon moves away
Researchers have found that as the Moon moves away, its gravitational pull on Earth is slowing the planet's rotation and gradually lengthening the length of the day. Thus, scientists predict that the length of the day on our planet may eventually be 25 hours. However, this will not happen in our lifetime – this process will take about 200 million years.
«As the moon recedes, the Earth becomes like a spinning ice skater who slows down as he stretches out his arms,» explains University of Wisconsin-Madison geologist Stephen Meyers.
The Moon is about 238,000 miles from our planet and takes about 27.3 days to orbit the Earth, the Daily Mail reports. But previous research has shown that the Moon is moving away from us by about 1.5 inches per year, meaning it will take longer to orbit our planet. At some point, the Moon will reach a stable distance and be visible from only one side of our planet.
For their study, Professor Meyers and his colleague reconstructed the deep history of the relationship between the Earth and the Moon. The scientists found that 1.4 billion years ago, a day on Earth lasted only about 18 hours.
To arrive at these estimates, the researchers invented a statistical method that couples astronomical theory with geological observations to peer into Earth's geological past. This allowed the researchers to reconstruct the deep history of the solar system. Billions of years ago, Earth's days were shorter, largely because the moon was closer to our planet, the scientists said. The researchers concluded that this caused our planet to rotate faster than it does today. But throughout Earth's history, the moon has been moving further away in a process known as «lunar decline.»
We know this thanks to astronauts on the Apollo missions, who installed reflectors on the Moon that allowed scientists on Earth to shine lasers on the lunar surface and accurately measure the speed of the Moon's recession, the Daily Mail notes. As the Moon gradually moves away, the Earth's rotation slows down. The reason for this is due to the influence of our planet's natural satellite on ocean tides. As the Earth rotates, the gravity of the Moon orbiting the planet affects the oceans, creating tides and the tidal effect. The Moon's gravitational pull causes ocean water to be «pulled» toward it from the side of the Earth that is closest to the Moon. At the same time, inertia tries to hold the water in place. But the gravity of the Moon is stronger, so the water rushes towards the Moon, says the Daily Mail.
Meanwhile, on the opposite side of the Earth, the Moon's gravitational pull is weaker simply because it is further away. There, the inertia is stronger than the Moon's pull, and the water tries to move in a straight line. This causes the water to move away from the Moon. The combined force of gravity and the Moon's inertia creates two tidal bulges, which stay in line with the Moon as the Earth rotates. But, the Daily Mail continues, the Earth rotates on its axis much faster than the Moon rotates around it. This means that the friction of the ocean basins moving underneath it also drags the water along with it. So the bulges move slightly ahead of the Moon's orbit, which tries to pull them back.
This gradually slows the Earth's rotation, while the Moon gains energy, causing it to move into a higher orbit. Other factors, including climate change, also affect the Earth's rotation, the Daily Mail emphasizes. As global temperatures rise, the polar ice caps are melting faster than ever before, spilling water into the Earth's oceans. All this meltwater is gradually moving away from the Earth's poles toward the equator, where the ocean is rising toward and away from the Moon. This has caused the Earth to become even wider at the center, and thus slow its rotation even further.
All this means that the Earth's day is gradually lengthening. The changes are so small that we will hardly notice them — they will not affect our circadian rhythms. But, as the Daily Mail notes, over millions of years these small changes will accumulate, eventually adding an extra hour to the Earth's daily cycle.