Interesting Facts about the Moon

by Fraser Cain on October 24, 2008

Want to stay on top of all the space news? Follow @universetoday on Twitter

The Moon. Image credit: ESA

The Moon. Image credit: ESA


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?

Reference:
NASA Solar System Exploration: Moon

About 

Fraser Cain is the publisher of Universe Today. He's also the co-host of Astronomy Cast with Dr. Pamela Gay.

Comments on this entry are closed.

Previous post:

Next post: