The Moon is Moving Away from the Earth

Is the Relationship Over? The most beautiful thing in a clear, star studded sky…is a full moon. Generations upon generations of modern day man has enjoyed the spectacular event of the Earths’ full moon. Even before man…the moon was there. Scientist say the moon has been around for 4.5 billion years. Now, that’s a long time!

They also believe both the Earth and the moon were formed at the same time, becoming locked in orbit with each other. Okay, you already know about the moons’ gravitational pull on the Earth. This is what causes our daily low and high tides, but the Earth also has a gravitational pull on the moon.

This force pulls the moon, causing it to become distorted into the shape of an egg, and creating tidal bulges on the surface of the moon. The Earths’ constant pull on these tidal bulges causes the rotation of the moon to slow down from its’ faster rate, to its’ present rate of 29.5 days.

The tidal bulges that are created on the Earth by the moon, are not exactly located directly below the moon. Instead, they are located slightly ahead of the moon, and because the Earth is spinning faster than the moon, this causes the gravitational force on the tidal bulge to pull on the moon, slightly increasing the orbital velocity, and when the orbital velocity of the moon increases, the rotation of the Earth slows.

It’s this unique relationship between these two bodies that is causing the moon to slowly move away from the Earth…about an inch a year. Although it’s not noticeable now, scientist say in about a million years, the effects will be very noticeable.

How Noticeable Will This be

How noticeable? Well, the tides will be much weaker, because of the weaker gravitational pull. When the tidal energy slows, the Earths’ oceans and crust will continue to slow our spin. The process will cause the days on Earth to become longer. Eventually, the result is that the Earth will show only one face to the moon, just as the moon does today.

Right now, our day is increasing at 0.0018 seconds each century, and the lunar orbit is increasing by 3.8 centimeters a year. Some scientist say 15 billion, while others say in 50 billion years from now, the orbit of the moon will stabilize at 1.6 times its present size, and for those of you who are always saying, ‘there’s not enough hours in the day’… a day on Earth could possibly be as long as 1,000 hours.

How Do We Know The Moon Is Moving Away

During the Apollo 11, 14 and 15 moon landings, apparently astronauts left retro-reflectors on the moon. Scientist can aim a laser pulse through a telescope at one of the retro-reflectors, and wait to see how long it takes for a return pulse. Since we know the speed of light, they can then determine how far the moon is from Earth. They also use orbiting satellites to take measurements, and they have been collecting data like this for over 25 years.

The question however, is will it really matter how long or how short an Earth day will be 15 or 50 billion years from now, and should we even care? These assumptions are based solely on the fact that Earth will still have liquid oceans at that time – to provide the tidal interactions necessary with the moon.

Scientist are also saying that as the sun evolves, the oceans on Earth will begin to evaporate, and the tidal interaction will be much slower, and in 1-2 billion years, the oceans will evaporate completely, and both the moon and Earth will have been eaten by our growing red giant sun!


Scientific American