Link #137: You Always See The Same Side Of The Moon!

May 2, 2016

Link #137: You Always See The Same Side Of The Moon!

Moon is the closest heavenly object to our planet in the universe. So, it’s not that surprising that mankind has always wanted to know more about it. For instance, we spoke about how the US government almost nuked the surface of the moon just to intimidate their opponent, Soviet Union, in our last article.

In fact, what we didn’t mention was that the Soviet Union had a similar program in place. Fortunately, both space powers decided to not pull the trigger. Who knows what a nuclear explosion on the moon could’ve done.

For all we know, we may have gotten to see the other side of the moon. After all, we’ve never really seen it before because only one side of the moon has ever been visible to Earth!

Can You Only See One Side Of The Moon?

Third Quarter Moon — *Image Credit: NASA Goddard Photo and Video/CC BY 2.0*

Most people don’t realize it but only one side of the moon has ever been visible to Earthlings. In fact, if you get a sequence of clear skies, then you’ll clearly be able to tell that the side of the moon you’re seeing is the same.

Because of this fact, astronomers and scientists have given the two sides of the moon different names. The side that is always facing the Earth is called the near side of the moon while the side that is turned away is called the far side of the moon.

Why Can’t We See The Far Side Of The Moon?

Moon's rotation and revolution around Earth — *Moon’s rotation and revolution around Earth. Image credit: Siyavula Education/CC BY 2.0*

In order to understand why you can’t see the far side of the moon, you need to understand how the moon rotates with respect to its revolution. Imagine yourself always facing your friend while making a round around him.

You will both revolve and rotate in a way that you will always be facing your friend. In other words, the time you take to rotate your body fully and complete a full circle around your friend will be the same.

Moon does the same thing to Earth (Please see Illustration above). In the case of the moon, the time taken to complete a full rotation and revolution is around 29.5 days. This phenomenon is called synchronous rotation or tidal locking. Because of this process, we only ever get to see about 59 percent of the moon.

What Is Tidal Locking?

*Tidal locking of the Moon with the Earth. Author: Stigmatella aurantiaca/CC BY-SA 3.0*

Tidal locking is a difficult concept to understand as it involves a wide variety of forces such as gravity, friction, and the masses of the bodies concerned. In the simplest of terms, you can explain tidal locking as a result of tidal friction between two bodies in space.

This tidal friction occurs when tidal forces on both the bodies go against each other. The tidal forces are caused by the gravitational pull of the two bodies. Finally, the gravitational pull of the two bodies is a result of the masses of the two bodies. The smaller the mass of one body with respect to the other, the quicker it will get tidally locked.

Moon has been tidally locked to Earth for millions of years. Typically, when tidal locking occurs, 50 percent of the smaller body is visible. However, since moon has an elliptical orbit around Earth, we can see 59 percent.