Flip-Flop: Did the Moon Do a Turnabout?

This seems like a good opportunity to ask ; Why is the moon more pitted with craters on one side ? I honestly haven't got a clue, and know nothing about it (apart from it being made of cheese). Please help me someone.

Only a thought, Kris, but is it possible, since the moon's gravity is only one-sixth that of earth, and the moon is (relatively speaking) very close to the earth, that Earth's gravity pulls the meteors which would hit at random, such that one side seldom gets hit, while the other is more "in the line of fire"?

This idea might not be able to sustain an attack of determined logic, but it's only 7:40 am here, and I'm still too sleepy to think it all the way through. I know its after noon, where you are, so when you come back to the keyboard, you'll probably be ready to tear this idea apart.

I'm interested in reading your thoughts on it.

Micah

The last parts of your post, #11, sum up pretty much what puzzles me. The more exposed 'dark side' is more evenly covered with craters. That would seem to make sense, but it begs the question, how many meteors (and over what time) did the Earth take the hit for ? OK, so the moon has a mix of volcanic and impact craters , but over time Earth must have had a lot of hits. I can only guess that the scale of time makes such events 'rare' (in our human concept of time), and impact's are by and large erased by tectonic activity, erosion, and weathering. There are however some well documented meteor craters on Earth ( Meteor Crater, Arizona, and Chixulub, Mexico), and impact evidence such as the KT boundary.

The Earths mass must have an effect on 'inbound', but I haven't the foggiest idea how much. Probably not much is my guess, but it depends on the direction and kinetic energy of the inbound. CR4 has many experts on astronomy, so I'm hoping this thread will gather pace and I can learn a bit more. Perhaps someone can clarify the moons surface structure in terms of how much is volcanic/meteor craters, and how much is lava flow ?

"I'm hoping this thread will gather pace and I can learn a bit more"

Amen to that!

The side with fewer craters may actually be the one that got hit more. If a lot of rocks hit, or some very large ones, the surface will heat up, turn molten and smooth out.

One would expect that the leading edge would be the one that got hit the most - just like your front windshield catches more rain than the rear.

Good point, but doesn't "leading edge" imply "the edge that is facing in the direction of travel"? I don't think that agrees with the actual orbital motion of the moon. It does not appear to be "pointing" ahead, but rather to be turning so that it describes a full "outward" rotation, every orbit of the earth, such that while it always has one side facing us, and indeed has one "point" facing (earth normal) north, and the other facing (earth normal) south, those aren't the "leading" sides. Rather, the side that best fits "leading" is the one that is away from us.

Of course that is predicated on the moon's orbit being in the plane of the earth's orbit. i.e., it travels around the earth such that its orbit send it alternately advancing and retreating along the earth's direction of travel.

I don't know if that is all true or not, and I can't draw diagrams on CR4 to explain what I mean, so I'll shut up now, and let someone better able weigh in on this.

Micah

The leading edge is the western hemisphere. Imagine a ball on the end of a string. You fling the ball around in a circle overhead, in a counterclockwise direction. When the ball is in front of you, the left hemisphere is leading edge, the right hemisphere is the trailing edge. The side with the string attached always faces you - the left side of that faces into the motion, the right side faces away from the motion.

But that's a direction relative to its orbit around the earth. Factor in earth's orbit around the sun and it becomes quite apparent that the moon doesn't have a constant "leading" face. Then you have to factor in motion along whatever direction the solar system is moving, then the galaxy, ad infinitum, ad naseum...

Hooker

The only motion that's relevant to asteroid impacts is the motion relative to the rest of the solar system. The western side of the moon is always leading it's motion. It's not a question of which way the moon is facing relative to the earth, sun or galaxy, just a matter of where the velocity vector of the moon points. It points west.

Sorry, I get a little confused when I'm dealing with 3D motion NOT fixed in relativity to the Earth. When you use West in this context, should I presume that's relative to a position standing on the Moon's surface?

And thank you for the answer. Clarifying this one point will bring it all into focus for me.

Micah

West relative to an observer on earth. When you look up at the moon, which side is pointing in the direction of the velocity vector? In other words, which side touches the horizon first? Since the moon travels east to west, it's always the west side. If there was a bunch of floating debris around the earth, that's the side that would bear the brunt of it. (If the debris was stationary relative to the sun, all of it would hit the western side and none would hit the eastern side, but since the debris is whizzing all around, only a majority would hit the western side.)

OK. So let's take it from the Earth's motion AND orientation relative to its orbit around the sun, and then take the moon's motion AND orientation relative to ITS orbit around the earth, and I think my question will become clearer.

The earth "rolls" at a steady once per 24 hours (+- a few seconds) while it is perigrinating around the sun, and has its axis of spin perpendicular to the plane of its orbit around the sun.

The moon does NOT roll around the earth, but does swing around it in a plane perpendicular to the earth's spin axis (it spins around the "waist" of the earth, instead of over its poles). Thus, since the moon doesn't spin relative to the earth (always keeps the same side facing us), its outside surface (relative to earth) is always facing directly away from earth's surface.

Thus, in the portion of earth's orbit that the moon is "ahead" of the earth, its outer surface faces any oncoming debris. During the portions of the orbit that the moon is either "moving ahead" or "moving behind" earth's position relative to the earth's orbit around the sun (the moon is "beside" the earth, but moving to either lead or lag it) the surfaces on the poles of the moon are most exposed to oncoming debris, and when the moon is behind the earth in the earth's orbit, the side facing the earth is facing oncoming debris. BUT, during the periods when the moon is "leading" or "following" in the trail, it's inner surface is always protected, either by its own mass, when leading, or by earth's mass, when following.

So, instead of all the impacts being on one side, it seems they should be distributed around the moon's surface with most of them falling naturally on the outside surface, relative to the earth, and the next higher incidence being around the moon's equator, at 90 degrees leading and lagging that side, with very few on the side facing earth. The poles would take equal numbers of "hits", somewhere in the middle of the total, but since those would always be at shallow "glancing" angles, they would create furrows, more than pits, with even that damage being modulated by the sideways travel of the moon's surface at point of impact, due to the moon's spin.

So, all that said, WHERE are the impacts showing up?

Micah

The impacts occur mostly in the western hemisphere (per the article).

Consider a lawn mower blade. Which side of the blade hits the grass? The leading edge - the edge that faces in the direction of the blade's velocity vector. Let the moon be the tip of the blade and the earth the hub, and pretend that the connecting blade is just gravity. Now assume that grass is flying by the blade from all directions. If the blade was standing still then it would be hit by grass equally on all sides, except where it is shielded by being in the shadow of the hub.

Now spin the blade. The leading edge will hit more of the grass - because it is driving into it. The trailing edge lies in the wake of the blade - the area that the blade has cleared away, and so gets hit less often.

That's the best I can do.

May be I am missing some thing from the original question. The original question, as I understood was if the surface of the moon flipped and now after 1959, we are seeing the other face of the moon? Yes, the hits would be on the face that is facing the earth.

Has any body seen the dark side of the moon or this face was dark side of the moon prior to 1959?

Yes the face should be the same as the moon is orbiting the earth so what is the big deal? Who cares which side of moon is faing the earth? However, I will stay with the forum to see how far the people's imaginations go. It will be amusing if not informative.

Regards;

Nadeem

The side of the moon facing the earth is the same as it has been for almost forever. But no one saw the other side of the moon until 1959.

Neither of these faces are what is addressed by the article, which speaks of the western (leading) and eastern (trailing) hemispheres, not the front and the back.

Then what happened in 1959? The moon is not rotating but orbiting so no way it will flip and bring the dark side facing the earth. That is bothering me and fail to understand. Or it is just a gimmick by the scientists who claim that the moon flipped.

Regards;

Nadeem

No one is claiming that the moon flipped in 1959. All that happened in 1959 is that the Soviets sent a probe to the other side of the moon and sent back some pictures. Until that moment, no one had ever seen that side of the moon.

The flipping of the moon referred to in the article happened millions or billions of years ago.

Thanks for expalining it.

I think there is an interesting and intelligent discussion is going on between duckinthepond andbhankii and I would stay to find out what you two learned ones come up with the sources.

I would not wait for 4.6 billion years and nor I will wait for 4.6 million or 4.6 thousand or 4.6 hundred or 4.6 decade to see about the moon flipping as no one is sure for even 4.6 years. But I will stick around to see where the conversation between you two goes.

Regards;

Nadeem

I totally agree that the solar system's and galaxy's motion is not relevant to this discussion. That was a totally failed tongue in cheek comment...

Maybe I'm missing something completely, but the hemisphere of the moon facing the earth's orbital path when it's on the sunward side of the earth is not the same hemisphere as when the moon is on the opposite non-sunward side of the earth. And since the primary approach vector of "most" asteroids is against the earth's orbital path, it would seem to me that the moon would take most hits from that direction with varying impacts between the two extremes.

Possibly I don't understand "western side of the moon".

Hooker

I am agreeing with hooker on this one. From the north the moon travels counter clockwise around the earth. That would make the eastern side the leading side. The moon only appear to travel to the west because of earths daily rotation. think this thru, the moon rises approximately one hour later each day. That means it it farther east compared to when you saw it rise the previous day. It just takes 29 days to get back to where it started after one rotation around the earth.

I think in the story that when they say eastern they mean the formerly eastern side which is now the western side after the 180 degree flip.

I read a lot of the followup posts, and gave up on trying to understand them all and decide which makes the most sense (or find the one authoritative answer that I can believe).

If I had access to one of those--don't know what you call them--those things that have spheres of various sizes with (usually) mechanical gearing, and access to a sandblaster, I'd be tempted to do some experiments. ;-)

Or, to be a little less destructive, use something softer than sand--not sure what that would be--ground up walnut hulls, flour (an explosion hazard) and coat the "moon" sphere with glue.

I don't immediately know which direction to aim the sandblaster, but I'm guessing that could be figured out--I guess at first thought, aimed toward the earth, from the direction the earth is traveling towards.

I guess someone could make a computer model as well.

Ok, after a little study of my own, I think the basic premise of the article (as presented) is wrong when it talks about the western hemisphere of the moon getting hammered more because it is the "leading" hemisphere. This seems to presume that the moon's orbit is the only significant factor.

The moon orbits the earth at 1.023 km/s.

The earth orbits the sun roughly 30 times faster at 29.658 km/s.

That means the moon's relative speed around the sun varies; 30 km/s +/- 1 km/s, or 30 times faster than around the earth.

There is no way you can convince me (who only has a rudimentary knowledge of orbital mechanics and some basic vector math) that the "western" (leading) hemisphere of the moon would have significantly more impacts than most of the rest of the sphere (excluding the relatively small area that is blocked when the moon is trailing the earth).

I'm sorry but the approach vectors of flotsam and jetsam would more than favor impacts more tangential to earth's orbit no matter where the moon is in its own orbit. This is why we're always advised to watch the eastern sky near sunrise for the greatest view during the regular meteor showers we encounter. They tend to come in nearly tangential to earth's orbit.

I'm more than willing to listen to corrections to the above as long as it takes into account the earth's orbit.

Hooker

Thought I'd put a spin on things here

The rotation of the moon—the time it takes to spin once around on its own axis—takes the same amount of time as the moon takes to complete one orbit of the Earth, about 27.3 days. This means the moon's rotation is synchronized in a way that causes the moon to show the same face to the Earth at all times. One hemisphere always faces us, while the other always faces away.

Factor in that it's slowing progression of .000237 arcseconds per year, extropolate that by 4.6 billion years and .................you get 109' (it was probably spinning a lot faster 4 billion years ago). Fast forward to 4.6 billion years from now and......the cratering of the dark side will probably look like what we see from the earth side today.

This is based on what again? The moon is tide locked to the earth, it will always have the same face towards us - due to it's lopsidedness and gravity. What am I missing?

Earth tides are pushing the moon away and are slowing it's rotation.

It's based on the slight differance between it's synchronous rotation around the earth which means that in time the dark side will be facing us.

Do you have a source for this? I can't believe anything unless I read it on wikipedia.

Not wiki. I'll see if I can find an online source for you. I think it would be found under Einsteinian geodetics or something like that. Maybe Einsteinian gravitation.

http://einstein.stanford.edu/content/sci_papers/papers/ParkinsonBW_1988_12.pdf

http://einstein.stanford.edu/content/sci_papers/index.html#nav

http://einstein.stanford.edu/MISSION/mission1.html

It's in here somewhere.........anyway......this is the gizmo they used to determine orbital analysis

There's a fair chunk on Earth Tides within CR4, but it depends how credible you think various people are. eg ; http://cr4.globalspec.com/thread/10065/Why-are-tides-high-OPPOSITE-the-moon contains some good stuff. You'll have to scan thru it a little to find the relevent bits.

For an "alternative" view (pun intended) of the moon find a copy of the book:

"Secrets of Our Spaceship Moon"

I'm not advocating it's conclusions just making readers of this thread aware of it. ;)