Why The Moon Is Getting Further Away From Earth

The Moon is not only beautiful, it is vital to our ecosystems and wildlife

The speed at which the Moon is moving away from Earth could affect life on the planet, but this could take billions of years to happen, writes space scientist Dr Maggie Aderin-Pocock.

It’s easy to take the Moon for granted, even on a clear night when it can light up the sky. It really feels as if it has always been there just as it is now, throughout history. But that’s not strictly true.

It is thought that the Moon was formed when a proto-planet about the size of Mars collided with the early Earth around 4.5bn years ago. The debris left over from impact coalesced to form the Moon. Computer simulations of such an impact are consistent with the Earth Moon system we see in the 21st Century.

The simulations also imply that at the time of its formation, the Moon sat much closer to the Earth – a mere 22,500km (14,000 miles) away, compared with the quarter of a million miles (402,336 km) between the Earth and the Moon today.

  The Moon continues to spin away from the Earth, at the rate of 3.78cm (1.48in) per year, at about the same speed at which our fingernails grow. Without the Moon, the Earth could slow down enough to become unstable, but this would take billions of years and it may never happen at all. The migration of the Moon away from the Earth is mainly due to the action of the Earth’s tides.

The Moon is kept in orbit by the gravitational force that the Earth exerts on it, but the Moon also exerts a gravitational force on our planet and this causes the movement of the Earth’s oceans to form a tidal bulge.

Due to the rotation of the Earth, this tidal bulge actually sits slightly ahead of the Moon. Some of the energy of the spinning Earth gets transferred to the tidal bulge via friction. This drives the bulge forward, keeping it ahead of the Moon. The tidal bulge feeds a small amount of energy into the Moon, pushing it into a higher orbit like the faster, outside lanes of a test track.

This phenomenon is similar to the experience one feels on a children’s roundabout. The faster the roundabout spins the stronger the feeling of being slung outwards. But the energy gained as the Moon is pushed higher is balanced by a reduction in the energy of its motion – so an acceleration provided by the Earth’s tides is actually slowing the Moon down.


6,000 years ago, the moon would have been about 800 feet closer to the earth.

While 3.78cm may not seem like much, this small difference over a long enough period of time could affect life on Earth, making the planet slow down. On early Earth, when the Moon was newly formed, days were five hours long, but with the Moon’s braking effect operating on the Earth for the last 4.5bn years, days have slowed down to the 24 hours that we are familiar with now, and they will continue to slow down in the future.

We can see some evidence of the slowdown in the fossil records of some creatures. By looking at the daily growth bands of corals we can calculate the numbers of days that occurred per year in past periods, and from this we can see that days are getting longer, at a rate of 19 hours every 4.5bn years.

The length of a day, or in other words the rotation speed of the planet, plays a big part in its stability.

Just like keeping a plate spinning on a stick, the key is to have the plate spinning fast, as if it slows down it crashes to the floor. In a similar way, as the Earth’s rotation slows down, our whole planet may start to slowly wobble and this will have a devastating effect on our seasons.

We have the seasons we currently do, due to the Earth’s tilt at an angle of 23 degrees on its axis. During summer the Northern Hemisphere is tilted towards the Sun so we get longer days and warmer weather. However in winter the Northern Hemisphere is tilted away from the Sun giving us shorter days and cooler weather.

If this were to change, and the Earth became unstable, then parts of the world could experience much greater temperature swings than we are used to through any given year, with freezing Arctic temperatures in winter followed by blazing hot temperatures in summer.

CGI enhanced image of what the Moon would look like if it was significantly closer

When the Moon was younger, it would have been much closer

As humans we have the ability to adapt to our local surroundings to meet our needs. If humans are still around when and if it happens it is quite likely we would survive these massive changes with air conditioning in the summer and a lot of heating in winter.

Unfortunately most animals are not so adaptable and if these changes happened rapidly due to an unstable planetary wobble, then most animals would not be able to evolve quickly enough to hibernate or migrate out of harm’s way.

The human race has little to fear at present. By the time any change occurred, humans might even have generated technology that could speed up the Earth’s rotation or transport us to other liveable planets within our galaxy. Source: BBC News


 Interesting Facts About The Moon



 Think you know everything there is to know about the Moon? Think again! Here are 10 interesting facts about the Moon. Some you might already know, and some will be totally new to you. Enjoy!

1. The Moon formed out of the Earth

Scientists now think that the Moon was formed when a Mars-sized object crashed into our planet about 4.5 billion years ago. The collision was so large that a huge spray of material was ejected into space. The orbiting ring of debris gathered itself into a sphere, and formed the Moon. How do we know that this is how the Moon probably formed? The Moon seems to be much less dense than the Earth and lacks a lot of iron in its core. Scientists think that the Moon is made up of the upper crust material, which has mostly lower density, than the composition of the Earth.

2. The Moon only shows one face to the Earth

Although the Moon used to rotate in the sky compared to our point of view, it has been slowing down billions of years. And at some point in the distant past it just stopped turning from our perspective. The Earth’s gravity holds the Moon in orbit, but it pulls differently at various parts of the Moon. Over a long period, gravity slowed down the Moon’s rotation so that it finally stopped, and always displayed one face to the Earth. A similar situation has happened with most of the large moons in the Solar System. In fact, in the case of Pluto and Charon, but objects are tidally locked to each other, so they present only one face to the other.

3. The Moon is slowly drifting away

Although the orbit of the Moon seems nice and stable, our only natural satellite is actually drifting away from us at a rate of 4 centimeters a year. This is happening because of the conservation of momentum in the orbit of the Earth. In about 50 billion years from now, the Moon will stop moving away from us. It will settle into a stable orbit, taking about 47 days to go around the Earth (it takes 27.3 days today). At that point, the Earth and the Moon will be tidally locked to each other. It will look like the Moon is always in the same spot in the sky. Of course, the Sun is expected to consume the Earth in about 5 billion years, so this event may not happen.

4. The Moon looks the same size as the Sun

This is an amazing coincidence. From our perspective here on Earth, but the Moon and the Sun look approximately the same size in the sky. Of course, the Sun is much much bigger than the Moon. The Sun happens to be 400 times larger than the Moon, but it’s also 400 times further away. This wasn’t always the case. Billions of years ago, the Moon was much closer than the Sun, and would have looked larger in the sky. And the Moon is moving away from us, so in the distant future, the Moon will look much smaller than the Sun.

5. The Moon causes most of the tides… but not all

You might know that the tides on Earth are caused by the gravitational pull of the Moon. But it’s not the only thing pulling at the Earth’s water, the Sun is helping out too. This is why we get very high and low tides from time to time. When the gravity of the Moon and the Sun line up, we get the biggest and smallest tides. Did you know that the Moon is also pulling at the crust of the Earth causing it to bulge up? You actually move a few meters every time the Moon is overhead, but you just don’t notice.

6. Gravity on the Moon is only 17% of the Earth

Want an easy way to lose some weight? Take a trip to the Moon and stand on its surface. Since the pull of gravity on the Moon is only 17% the pull of gravity on the Earth, you’ll feel much lighter. Just imagine, if you weighed 100 kg on the Earth, you would feel like you only weighed 17 kg on Earth. You would be able to jump 6 times further and carry objects 6 times as heavy. In fact, you had wings attached to your arms, you could even fly around inside a dome on the Moon under just your own muscle power.

7. The official name for the Moon is… the Moon

I know it’s kind of confusing, but the only real name for the Earth’s Moon is “the Moon”. When the Moon was given its name, astronomers didn’t know that there were moons orbiting other planets. And so they just called it the Moon. Now that we know there are other moons, it all comes down to the capitalization. The Earth’s moon is referred as “the Moon”, with a capital “M”. Other moons are given a lowercase “m” to show the difference.

8. The Moon is the 5th largest natural satellite in the Solar System

You might think that the Moon is the largest satellite in the Solar System. I mean look at it, it’s huge! But there are actually larger moons in the Solar System. The largest moon is Jupiter’s Ganymede (5,262 km), followed by Saturn’s Titan, Jupiter’s Callisto, Jupiter’s Io, and finally, the Earth’s Moon with a mean diameter of 3475 km.

9. Only 12 people have ever stepped onto the surface of the Moon

Only a tiny group of astronauts have ever set foot on the surface of the Moon. These were the astronauts on board the Apollo missions going from 1969 to 1972. The first person to ever walk on the Moon was Neil Armstrong. And the last person on the Moon was Gene Cernan, who followed his partner Jack Schmitt into the lunar lander on December 14, 1972.

10. And we’re going back to the Moon

NASA has been given the mission to return humans to the Moon, and set up a permanent research station. At the time of this writing, astronauts are expected to set foot on the surface of the Moon again in 2019.

Want more information about the Moon? Here’s NASA’s Lunar and Planetary Science page, and here’s a link to NASA’s Solar System Exploration Guide.

You can listen to a very interesting podcast about the formation of the Moon from Astronomy Cast, Episode 17: Where Did the Moon Come From?


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