I've heard we only ever see one side of the moon. Is this true?

Question

If it is true that we never get to see the "dark" side of the moon, then does anyone know why it is that the moon doesn't rotate like the earth?

Answer 1

Yes, it is true. From the earth we only see the same side of the moon.

This is because the moon IS rotating, but at the same speed that it is orbiting ... so the same side is always facing us.

Traditionally we have called the side facing away from us the "dark side" of the moon, but this is an incorrect name. it is not always dark, but sometimes the side facing the sun (bathed in sunlight) is not facing in this direction. In general half of the moon is *always* illuminated by the sun (except during a lunar eclipse) ... so when you see a crescent moon, you're seeing the edge of what is facing the sun.

Here is the first picture taken of the far side of the moon ... by the Russian spacecraft Luna 3 on October 7, 1959.:
http://en.wikipedia.org/wiki/Image:Luna3mosaic.jpg

Better pictures were taken by the Apollo missions.

Here is an entire wiki page on the far side of the moon (including quotes from Pink Floyd's "Dark Side of the Moon" album. :-) )
http://en.wikipedia.org/wiki/Far_side_of_the_Moon

Answer 2

Well, err, not exactly.

One side of the moon always faces earth, so YOU have only ever seen one side. But of course, MEN have seen the other side, since the apollo moon missions and various lunar orbit satalites have photographed the "far" side many times.

Next, the moon DOES rotate. As it orbits the earth it rotates once each orbit so that the same side is always facing the earth. This is called "Tidal lock" and it is held in place by the same forces that cause the tides each day on earth.

So, Finally, there is no dark side, only a FAR side. The far side is light when the near side is dark ( A "new moon" ) and the far side is dark when the near side is light (a full moon) THis happens once a month.

Answer 3

Yes, the moon is lock into an orbit where it's period of revoulation is equal to it's period of rotation. This was caused by tidal force.

Just a bit of advice, call it "the far side of the moon", not the "dark" side.

Answer 4

Actually, the moon DOES rotate. Millions of years ago, the moon rotated much faster than it does today, however, because of tidal forces (gravity between the earth and moon), it has slowed down, and is tide-locked with the rotation of the earth.

Answer 5

the same side of the moon is always facing earth..and the moon does rotate & revolve like earth...it takes about i think 27.3 days to complete its full cycle (moon phases)

Answer 6

We actually see slightly more than "one side of the Moon," although not very much more.

The Moon is essentially "tidally locked" to the Earth, so that as is orbits the Earth in space, it is also rotating with one face pointing towards the Earth. However, there's (literally) a slight twist or two that I'll get to, later.

If you still find this hard to imagine, here's a simple experiment.
First find two or more friends, a basketball, and a flashlight. Hold the basketball out at arms length, with the nozzle or something else easily identifiable stuck onto the side of the basketball away from you. (Leave the flashlight alone for the moment.) Now rotate slowly around while your friends watch the basketball. You will keep on seeing the same face of the basketball. However, your friends will see the nozzle or other feature rotating around. As you turn once around, your friends will see the basketball rotate once in space.

This is analogous to what the Moon is doing, making one rotation in space per month, while we on Earth see none. In fact, no matter what the actual rotation in space of any orbiting object, outside observers who watch it will always differ with someone at the orbit's centre by exactly 1 rotation, when counting the number of rotations per orbit.

As to calling the opposite face of the Moon "the dark side," how anthropocentric is that?! When you look at anything on Earth, is the other side of it the "dark side?" Does light only radiate from YOU?!

Do the previous basketball experiment in a darkened room, after giving one of your friends the flashlight. Imagine he or she is the Sun, and have them shine the light onto the basketball as it rotates. You will then see the successive "phases" of the lit-up basketball, and while you are seeing part of the full illumination, your friends will see light on part of what you call "the dark side." In fact,when you see nothing on your side, at precisely "New Basketball" (like you can't see the Moon at precisely astronomical "New Moon"), the so-called "dark side" is FULLY ILLUMINATED.

Now to the slight "twists" I mentioned early on. The Moon's orbit is eccentric, so its distance from Earth varies by +/- 5%. Because of this, its angular speed in its orbit varies up and down by +/- 10%. Since the Moon is a very large body, IT continues to rotate at an essentially constant rate in space; there's simply no way that Earth's tidal forces can operate in a mere month to keep the Moon "tidally locked" to the Earth on a month-long timescale. The result is that:

THE MOON ROCKS!

By that, I mean that from Earth, we see the Moon appearing to be sometimes ahead in its orbital position relative to its spatial rotation, and sometimes behind it. So we see "a little bit around the corner" of the usual "face", on opposite sides at about two week intervals. (Some astronomy texts have pictures showing some features on the right or left limb that are present in one of the pair, absent in the other.) Let's call that a "horizontal rocking."

There's another, "vertical rocking." This is a bit harder to visualize. The Moon's orbital plane is "tilted" at about 5 degrees to the Earth's orbital plane. Also, the Earth's spin axis is also "tilted over" by about 23 1/2 degrees. Because of that, anyone on the spinning Earth will see slightly over or under the average "top of the Moon" at different times in the month.

The net result is that we see slightly more than half of the Moon's surface. (I think it's about 53%, with no guarantee.)

A corresponding point is this. At any moment, there's a point on the Moon that is DIRECTLY under the Earth. For that point, the Earth is directly overhead. (It's called the "sub-Earth point.) Now, because of the Moon "rocking," that point will wander around on the near face of the Moon. You can draw an ellipse-like shape on a picture of the Moon's near face, and at some time during successive months, the "sub-Earth point" will wander around within this ellipse.

Finally, the Moon used to rotate faster in space, but it wasn't completely spherical. Earth's gravitational "tidal" forces acted on the equivalent of the Moon's "bulges," changing its rate of rotation in space. It's a complicated long-term story, that also involves dissipation of some gravitational tidal energy in the Earth's oceans. The end result is that the Moon has backed off from the Earth, its original orbital period has lengthened until it got "locked" with one face towardsEarth as it is now, and the length of Earth's day has also changed. The long, long distant future probably involves a much longer month still, with Earth's rotation itself locked with the Moon --- two ballroom dancers doomed to face one another for ever!

I hope this helps.

Live long and prosper.

Answer 7

yes we only see one side of the moon
the time period of the rotation of earth about its axis is equal to the time period of the revolution of the moon about the earth. therefore we see only one side of the moon

the far side of the mooon is always dark and there are no clear photograps of it.
therefore we see only one side of the moon

Answer 8

yes it is true. not sure exactly what the proper mechanics consist of but it does have something to do with the gravataional field of the earth and that of the sun.