The Moon is fixed

[notthecheatr]

Why is it that the moon always shows us the same face - it does noot rotate on its axis relative to the Earth - is this normal or is our moon a special moon?

"Special" is a matter of opinion. There is, to my knowledge, no scientific test for specialness. Or if there is, it exists in psychology, not astronomy

The moon is special to us because it is our moon. Tidal lock may seem surprising, but as many moons as there are out there I'm sure it's not really that unique.

What exactly is your point here?

[morphius]

Because it rotates at the same rate that it orbits Earth.

Why does it rotate at the same rate as the earth?

or...

why did “it became gravitationally locked to the Earth.”

[Zeebadee]

Eventually, the earth will establish the same relationship with the sun - one half of the earth will cook.

[notthecheatr]

Why does it rotate at the same rate as the earth?

or...

why did “it became gravitationally locked to the Earth.”

Sometimes it helps to read what other posters have said as a response to the question before asking the same identical question... just sayin

Some more, some of which I was not aware:

Relative to the Earth, the Moon makes one rotation every 29.5 days. That happens to also be the time it takes for the Moon to complete one revolution around the Earth. This might seem like a coincidence, but it's not.

In the past, the Moon used to rotate much faster than it does now. But over millions of years, the effect of the Earth's gravity has slowed down the Moon's rotation until it became gravitationally locked to the Earth. This is why we always see the same side of the Moon.

It would seem logical to say that at any one time we can see 50% of the Moon's face. If the Moon were flat, that would be correct, however we know the Moon is a sphere. And the spherical shape of the Moon hides the area close to the perimeter and we can, at any one time, see only 41% of the Moon's face.

Even though the same side of the Moon's faces us, we do see a bit more than half of the Moon's face. Over time, because of librations, we can see up to 59% of the Moon's surface.

Librations are irregular motions of the Moon in its elliptical orbit around the Earth. They are measured using longitudinal and latitudinal coordinates. Both are computed from a central point that is at a fixed geographical location on the lunar surface. This point is in the Sinus Medii, a small plain just below and to the right of he large rayed crater Copernicus. Two meridians emanate from this point: the Central Meridian runs north and south, and the Lunar Equator runs east and west.

Different librations affect different sides of the Moon and each contribute added surface area. The added viewable surface area changes from day to day and month to month. Some librations overlap, but the maximum amount of lunar surface that we can see over time is 59%.

The longitudinal libration is produced by the elliptical orbit of the Moon. Because of the nature of the elliptical orbit, the speed of the Moon changes depending on which part of the orbit it is in. When moving from its fastest point (closest to Earth) to its slowest point (farthest from Earth,) the Moon's speed is slowing down. But, because the Moon's rotational speed stays the same, for a period of time the Moon's face is not pointed directly at us, and this "lag" effect allows observers to see an extra bit of the lunar surface. In effect, we are "peeking" around the edge of the Moon! When the Moon is one quarter of the way around the Earth, it is 97 degrees through its rotation.

This libration is called longitudinal because the extra surface areas exposed are along the lines of longitude (perpendicular to the equator.) The total extra surface area we can see from longitudinal librations is about eight degrees.

There is also a libration that is latitudinal. The plane of the Moon's orbit is titled 5 degrees to the ecliptic. For half the lunar cycle, the Moon is above the ecliptic and for the other half it is below the ecliptic. Each of these half cycles expose an extra bit of the Moon. The extra surface area shown during these librations is at the top of the northern hemisphere or the bottom of the southern hemisphere. The total extra surface area we can see from latitudinal librations is almost 7 degrees.

There is one more librations called Diurnal Librations. This librations occurs every day. Observers can "see" over the top of the Moon as it is rising. Likewise they can see under the bottom when it is setting. Diurnal librations are caused because the radius of the Earth adds an extra 4000 miles of height for looking "over" or "under" the Moon when it is on the horizon. This daily libration gives us an extra one percent of lunar surface area for viewing.

Why do We See only One Side of the Moon?

[morphius]

Sometimes it helps to read what other posters have said as a response to the question before asking the same identical question... just sayin

where do you think I got the quote of “it became gravitationally locked to the earth.” :)

as a matter of fact, I would like to review the papers where this statement came from? IOW, how did they come about this conclusion? Did they do an experiment in a lab to come up with that? Where is this model of their findings?

There are a lot of questions that need to be answered in more detail.

I believe that the best (short) answer was given by friedrichseneca, and I read wiki about all that but was still not satisfied with the evidence.

So that explanation does not answer the why that occurs. And I don't believe one knows why exactly but I would like to now how one came about that conclusion, hey, in lay mens terms as possible that is :)

I just go (try to go) by the philosophy of “Tell a man there are 300 billion stars in the universe and he'll believe. Tell him a bench has wet paint on it and he'll have to touch to be sure.”

believe it or not, what you can understand is not that hard to understand by the rest.

So why is it that the moon becomes oval and from the oval shape, one half is more affected by “earths gravitational pull” than the other side?

Also, that means that all sides of the moon have been “locked” to earth at some point. That means there is a time of how long one side of the moon is “locked” to the earth.

I am expecting a real good answer from you :)

[Dan74]

You can come to that conclusion through basic science skills and observation.

[Angry Citizen]

Put simply, gravitational 'locking' occurs because gravity's effects trail off as a function of the inverse square of distance (in other words, it decreases dramatically with distance). One half of a spherical body is always being affected by higher gravity than the other half. This creates something similar to a 'drag' effect on the rotation of the body. Given eternity, all bodies in orbit will become gravitationally locked to one another; however, eternity does not really exist for our purposes, and thus only smaller bodies in very close proximity to a larger body will undergo gravitational locking, such as Mercury to the Sun, and the Moon to the Earth.

[morphius]

You can come to that conclusion through basic science skills and observation.

I can understand your logic behind this claim. And that is from arrogance and beliefs of being able to understand more than the rest with just very little of explanation. Which that is fine and dandy... anyone can give short answers. For all I know you could have googled and gave a very short answer “Because it rotates at the same rate that it orbits Earth.”... which I believe you did. But that does not really mean that you know what you are really talking about.

Now define “basic science skills”? I hope you are not just defining your own skills (googleling skills?) of know how as “basic skills”?

Also, observations are subjective. Yeah, you might believe that “your observations” are unique, and they are, but they are not really that unique that other people cannot understand. IOW, you just want to make yourself look good :)

All I ask is for you to explain the beginning. I don't want to hear the middle or the end, I want to hear the beginning. I believe that everyone does.

But I have a feeling that you cannot because you just want to bully. So I just had to say what I had to say 'cause I believe that I have basic science skills and basic observations too, but when did those basic skills make everyone who poses the basic skills understand anything?... specially those with the advance skills? So all who poses the basic science skills and the basic observation skills understand anything? just the basic skills, right? or, should i say, your basic skills of knowing how to use google.

In what school grade did they teach these basic skills? (in what grade did they teach about the moon being locked to the earth?)

[morphius]

Put simply, gravitational 'locking' occurs because gravity's effects trail off as a function of the inverse square of distance (in other words, it decreases dramatically with distance). One half of a spherical body is always being affected by higher gravity than the other half. This creates something similar to a 'drag' effect on the rotation of the body. Given eternity, all bodies in orbit will become gravitationally locked to one another; however, eternity does not really exist for our purposes, and thus only smaller bodies in very close proximity to a larger body will undergo gravitational locking, such as Mercury to the Sun, and the Moon to the Earth.

Thanks for the answer but I want to go deeper, starting from where the person who discovered this... e.g. was it from the micro world? e.g. studying some protons and neutrons? Or by measuring the moon radius? Stuff like that. Then do they base all other “locking” on that?

Now, if they base “locking” on the micro world, then the big world follows the same laws as the micro world? If they do, then our galaxy is locked to something bigger too. I mean why not?... based on that "basic" understanding.

Now, if gravitational pull is “different” in the micro word than in the big world, (we may call it “attraction” in the micro world and gravity in the big world) then we cannot assume our findings in the micro world are the same findings in the big world, IMO. I just want to know from the beginning, or as close to the beginning as the last (knowledgeable) person understands.

But thanks anyways for the answer. That makes sense from my “basic skills.”

[gallo]

Thanks for the answer but I want to go deeper,

That's nice and all, but I don't think that this board is a place where that desire has a chance to go much deeper than the answers already given. You are asking about a very specialized field known as planetary physics. I used to know a JPL planetary physicist (physics and astronomy) who posted to several boards, especially creationism v. evolution boards, but I haven't seen him around for several years and he never posted to this board.

I must say that I am completely at a loss on this topic. Some people on this board think that I weigh in every topic. But that's not true. I actually only address those fields in which I have acquired some specific knowledge. Planetary physics is not one of those fields.

I think that you have already received the best answer you are going to get from Angry Citizen. That answer seem logical to me.

For more information, I think that you will have to enroll in some astronomy/physics program in a university. Good idea.

[Angry Citizen]

I don't know how it was discovered. I can tell you, however, that classical mechanics is what applies to tidal bulging and other effects which cause the phenomenon, not quantum mechanics (I'm assuming that's what you mean by the distinction between the macro and micro world).

Imagine if a football were orbiting the Earth. The football's elongation is analogous to the tidal bulging caused by the Earth's gravitational field. (Side note: This would be much easier if I could just draw the pictures, but alas.) Imagine if the ends of the football WERENT constantly pointed at the Earth. What would happen? Well, the ends would have a torque exerted on them by the uneven gravitational conditions (see my previous post on the inverse square nature of gravitational force). This induces a rotation that is either counter to the innate rotation of the body (if it's spinning too fast for tidal locking to take place) or consonant with it (if it's spinning too slowly). Given sufficient time, tidal locking is an inevitability in all gravitational systems.

However, you're incorrect that the Milky Way is tidally locked with another system. This betrays a misunderstanding of what I said earlier. The Milky Way is not rotating around another galaxy which is close by. This is a prerequisite for any observed instance of tidal locking. Body A (which we take to be the larger of two masses) much always be in close proximity to body B (which we take to be the smaller of the two). Examples include the Earth/Moon system, the dwarf planet Pluto and its companion Charon, and assuming the existence of Gliese 581g is ever confirmed, it too is likely to be tidally locked. What do these systems have in common? Very, very short orbital radii. In the case of Pluto, it's interesting to note that it is also tidally locked to Charon, just as Charon is tidally locked to Pluto. This is a result of the relative lack of mass inequality in the system.

One doesn't need an astronomy or physics program to understand this. A mechanics (read: not the guy who fixes your car) class will teach you everything you need to know about torques and gravity wells to understand why the moon and other bodies are tidally locked. (Side note: The term 'gravitational locking' has been bugging me ever since I came into this thread, and I only recently remembered why. The appropriate term is tidal locking.) However, if you give me a couple years, I'll be happy to apply an aerospace engineer's orbital mechanics class to this thread -- although at present I don't see much of a need to.

[juliettelixora]

That's nice and all, but I don't think that this board is a place where that desire has a chance to go much deeper than the answers already given. You are asking about a very specialized field known as planetary physics. I used to know a JPL planetary physicist (physics and astronomy) who posted to several boards, especially creationism v. evolution boards, but I haven't seen him around for several years and he never posted to this board.

I must say that I am completely at a loss on this topic. Some people on this board think that I weigh in every topic. But that's not true. I actually only address those fields in which I have acquired some specific knowledge. Planetary physics is not one of those fields.

I think that you have already received the best answer you are going to get from Angry Citizen. That answer seem logical to me.

For more information, I think that you will have to enroll in some astronomy/physics program in a university. Good idea.

its not a bad idea that we have some general knowledge about some queries and some certain things. But based on my experience the more we tend to learn the more we realize how few our knowledge is.

And speaking about going to school or university well know a days it's more like of the same thing learning online. But the advantages about learning online and especially learning alone is that no one can guide you to the learning process. No teacher or professor to correct you from your wrong beliefs.