Why can't we see the dark side of the moon?

Question

I know the answer seems obvious, but it seems like when you see the moon in the sky its always the same sky with the craters in the same formation. Why is it that we never see the other side? I really am curious so don't blast my question please.

Answer 1

Well it's true that from the dark side of the Earth you can always see only the same side of the moon. But that doesn't mean the moon is always facing us with that side only.
The situation is that the moon's rotation and orbit around earth just so happen to be synchronous.

Synchronous rotation is when the body that's orbiting (this case, the moon) around another body (Earth), takes the same time to orbit around it's own axis as it does to make one orbit around the other body.
So, the moon needs the same time to rotate around the Earth as it takes to rotate around it's own axis, which is 27.32 days.

That is why when we see the moon at night we always see only one hemisphere. If we could have seen the moon when it was day on Earth, we would have noticed that the other hemisphere was facing us.

But the Earth and the Moon are not the only case of a synchronous orbit.
This is also the case with Pluto and it's satellite Charon, Mars and both of it's satellites Phobos and Deimos, and other celestial bodies.

Here is also an image that shows how the synchronous rotation works:
http://ircamera.as.arizona.edu/astr_250/images/moon_rot.JPG

Answer 2

First, the "dark side of the moon" is a misnomer. The far side of the moon is brightly lit up half the time, but since it's always facing away from us, we never get to see it.

Now, the moon's rotation exactly matches it's revolution, so that in the time it takes to go one orbit around the earth, it turns so that the same side is always facing the earth. It's like if you walked in a circle around someone, but always turned to face him because you were afraid of him or something.

The reason why this happens is not well known, but most scientists believe it has to do with how the moon came to be created (they think a large chunk of the earth was blasted off by a collision with a another planet). That chunk became our moon. Long ago, the inside of the moon was somewhat squishy, and was affected by the earth's gravitation. The result was that the moon's rotation was affected until it slowly came to match the motion of the moon orbiting around the earth, which is why we only see the near side today.

Answer 3

Actually it is the hidden side, not the dark side. The side we see does get dark (when we see a crescent, it is because only a small portion of the side we see is lit, the rest is in the dark).

The reason that we only see one side is that the orbital period of the Moon around us (a month) and its rotation period are the same. It is turning on itself at the same rate as it is turning around us.

The reason it does that is called tidal "spin-lock". We know the Moon raises tides in Earth's ocean. What is less apparent is that the Moon also raises tides in Earth's crust and mantle. Because rocks flow a lot less than water, they are more difficult to measure, but they are there. And the tides are slowing down Earth's rotation by a very tiny bit.

Earth is far more massive than the Moon. Therefore, Earth raised far higher "rock" tides on the Moon (about 50 times more). These tides were enough to slow down the rotation of the Moon until it matched the orbital period.

The Moon's tides are still slowing down the Earth. Because the Earth is more massive and because the Moon's tidal force is less than Earth's, Earth's rotation has not yet slowed down to match the Moon's motion. This will take billions of years.

If the Earth-Moon system survives long enough, one day only one face of the Earth will be visible from the Moon. People living on the "wrong side" of Earth will not see the Moon.

Answer 4

The moon is "tidal locked" - it's period of rotation matches it's period of orbit. One side always faces Earth, and it's because the moon's center of gravity isn't right in the center - it's denser a few hundred miles outside it's core than on the other.

Think of a dumbbell floating in orbit, spinning. For a brief period of time, the large end pointing to Earth is attracted FAR more than the far large end, and this tends to slow it's rotation. Given enough time, that dumbbell will slow such that one large end is always pointed toward Earth, and the far large end is always pointed away - that's what happened with the moon.

Answer 5

To make it even simpler than these good explanations, hold a ball in your hand at arms' length and slowly spin your body, you always see the same side of the ball, but your friend 20 ft away sees all sides of the ball as it rotates AND orbits.

Answer 6

This is actually quite simple.
Because the earth is larger gravity forces the "face" of the moon to always face the earth.
The moon does not spin because it lacks an active core, and is too small to escape Earth's grasp.

Answer 7

there is a simple awnser to this question.......if you remember, we had learnt in junior classes that for the MOON...
1revolution(around the earth)=1 rotation
if u still don't understand what i mean....then......take a ball with a string. hold the string and then rotate the ball in a circular motion. you will see the same side of the ball (when u are facing it). that is because rotation is happening along with revolution.

Answer 8

as well as moving around the earth, the moon is also rotating on it's own axis (spinning around). It's a matter of the moving and the spinning working together in just the right way.

Try it yourself with an apple or orange. I agree that it is a tricky idea until you sit down and think about it :)

Answer 9

I will tell you my experiences with naked eye..
if you concentrate on Half moon, you can see its other half (faintly, infact very very faintly) but thats too too too difficult..
However, you cant see that because it is not reflecting any light from the sun.. the part of the moon which receives te sunlight is visible as moon has no light of its own!!

Answer 10

lol... Ask Pink Floyd