Since the universe is expanding, did early man see a different moon than what we see now? Wouldn't it have been closer?

If there had been 2 moons a the very beginning, how would we ever know?

There is evidence that the Moon is still slowly moving away from Earth. What amazes me is the speculation of how the Sun is 400 times larger than the Moon, but the Moon is 400 times closer to Earth than the Sun, accounting for some spectacular eclipses. Though I don't know about a second moon.

Though I don't know about a second moon.

Cruithne:
http://en.wikipedia.org/wiki/3753_Cruithne

Since the universe is expanding, did early man see a different moon than what we see now? Wouldn't it have been closer?


Objects as local as the moon certainly do not move away due to expansion of the universe.

Objects as local as the moon certainly do not move away due to expansion of the universe.


so our moon has always been exactly the same distance away, just like we have always been exactly the same distance from the sun? So that would be proof that we have never had another moon right? (sorry Oli, that 'moon' doesn't count :p )

so our moon has always been exactly the same distance away, just like we have always been exactly the same distance from the sun? So that would be proof that we have never had another moon right? (sorry Oli, that 'moon' doesn't count :p )

No I'm not saying that, I'm just saying that because of gravity even the galaxy isn't even moving apart due to expansion.


Asking whether we never had more than one satellites is pointless.

..Asking whether we never had more than one satellites is pointless.


why??:confused:

How big? How long for?Is the Planetesimal stage of the earth included?

so our moon has always been exactly the same distance away, just like we have always been exactly the same distance from the sun? So that would be proof that we have never had another moon right? (sorry Oli, that 'moon' doesn't count :p )

No. Due to friction the moon is constantly moving away from Earth. Before it was closer to Earth than now, and on Earth the moon influence was much stronger. We are the lucky ones to see the moon and the sun with the same angular sizes. Later the moon will be further, and Earth will be more susceptible to killer asteroids.

No. Due to friction the moon is constantly moving away from Earth. Before it was closer to Earth than now, and on Earth the moon influence was much stronger. ..

so eventually we will have no tides?

Correct. At the point where other planets' and Sun's influence on the moon becomes stronger than that of Earth on the moon, the moon will become a minor planet of the solar system or it will be ejected from the solar system.

Correct. At the point where other planets' and Sun's influence on the moon becomes stronger than that of Earth on the moon, the moon will become a minor planet of the solar system or it will be ejected from the solar system.

How will it be ejected? Will it just go floating off or will another planet grab it?

If it will be ejected, it will be because of the gravitational slingshot effect. If it is not, some planet or the Sun will grab it making it their sattelite.

Correct. At the point where other planets' and Sun's influence on the moon becomes stronger than that of Earth on the moon, the moon will become a minor planet of the solar system or it will be ejected from the solar system.Not correct.

The sun already has greater gravitational effect (stronger force) on the moon than the Earth does. (If you do not believe, calculated the relative Mass/separations^2 ratios for both sun and Earth (except for factor "G", the gravitational force at the moon).

In fact, the moon is now going arround the sun in essentially the same elliptic orbit as the Earth is. I.e. The moon only appears to be going around the Earth when viewed from the Earth. In fact, it is always with a trajectory that is curving towards the sun. Never is the moon on a trajectory that is convex towards the sun (as you would expect it to be if it were going around the Earth like most man made satellites are).

If the Earth were magically removed there would be very little difference in the moon's orbit about the sun. That orbit now has slight
"wobbles" about the true ellipse, which are caused by the relatively weak gravity from Earth and of course if Earth disappeared or had no gravity, they would cease to exist, but viewed from Mars, it would not be a noticable change in the moons orbit if the Earth had zero gravity. Earth does NOT control the moon. Really Earth does not have a natural moon, but is the larger of two interacting masses that co-orbit the sun.

Thread is badly named, reflecting this common erroneous POV. Should be called "Sun's planatoid near Earth" or something like that.

...Thread is badly named, reflecting this common erroneous POV. Should be called "Sun's planatoid near Earth" or something like that.

LMFAO!! You have got to be kiddin' me. :rolleyes:

Thanks for all the other info though.

I agree the point where the influence of the other objects becomes more than that of Earth would not necessarily decide whether the moon is a sattellite of Earth or not. Wikipedia says that the Moon will continue to move slowly away from the Earth until the tidal effects between the two are no longer of significance, whereupon the Moon's orbit will stabilise.

What amazes me is the speculation of how the Sun is 400 times larger than the Moon, but the Moon is 400 times closer to Earth than the Sun, accounting for some spectacular eclipses.

That is really peculiar ain't it?

And it's so big relative to the Earth.

psik

Since the universe is expanding, did early man see a different moon than what we see now? Wouldn't it have been closer?

It used to be closer than it is today, but that has nothing to do with the expanding universe. The expansion of the universe essentially doesn't affect anything in our galaxy, or anything in our solar system. Local gravitational effects dominate there.

If there had been 2 moons at the very beginning, how would we ever know?

During the formation of the solar system, there were probably hundreds of moons flying around. Some ended up as part of the Earth; some formed our current Moon; some ended up in orbits completely different from the Earth; some were swept up by Jupiter. Some ended up as asteroids.

Objects as local as the moon certainly do not move away due to expansion of the universe.

I don't see how you can count on that. It depends on what theory you hold to, but if space itself is expanding, stretching out, I think that while the moon doesn't actually "move" further away the space between the Earth and the moon becomes longer.

I don't see how you can count on that. It depends on what theory you hold to, but if space itself is expanding, stretching out, I think that while the moon doesn't actually "move" further away the space between the Earth and the moon becomes longer.
:roflmao:
No it depends on whether you adhere to data like redshift and flux of stars in our vicinity, which show no trends of recession.

To be honest any so called theory you say has an object as close as moon receding from the earth oposing gravity confinment should be grounds for the author to be commited.


The friction explanation is the right answer.

In fact I've just looked it up and the local group is even confined - theres no trend of recession within the local group.

So our universe will stay the same, we will just get farther away from other universes?

So our universe will stay the same, we will just get farther away from other universes?

No the local group(our cluster of galaxies) and every thing there-in is still jossling(if you like) its just not itself expanding. Anything beyond in the visible universe is moving away from us at the hubble constant.

I agree the point where the influence of the other objects becomes more than that of Earth would not necessarily decide whether the moon is a sattellite of Earth or not. ...You are getting closer to the truth / correct understanding in this post, compare to the one I said was "not correct," but still error in the parts of your post above, which I made bold.

That "POINT" is not some time in the distant future, but was passed millions of years ago. The sun, not the Earth, has long been the dominate gravitational force on the moon. The moon is NOT a "sattellite of the Earth," but a body orbiting the sun, almost as if the Earth did not exist!!!!

It is difficult to imagine that the Moon comes on both sides of Earth 12 times per year but still moves in a trajectory always curved towards Sun. But since the gravitational attraction of Sun is stronger it should always be curved towards Sun.

I think it somehow does not matter how strong Sun's gravitation is, the Moon is always Earth's sattellite. Because the Earth-Moon system falls freely in Sun's gravitational field and so the Moon moves around Earth as if there was no Sun.

The Moon is a satellite of the Earth, not a separate planet. That the Sun exerts greater gravitational force on the Moon than does the Earth is not the correct metric for determining the Moon's status. The Moon lies inside the Earth's Hill sphere (http://en.wikipedia.org/wiki/Hill_sphere).

That is very interesting. So the Moon can have its own sattellite, and that one having own tiny sattellite and so on.

The Center of Mass, CoM, of the Earth/moon system is in elliptical orbit about the sun (neglecting the effect of Jupiter, etc.). Both Earth and moon "wobble" (the moon more than Earth) about this ellipse. The wobble of even the moon is so small, compared to the 1AU separation from the sun, that the moon's trajectory is always curving towards the sun. Both Earth and moon can be considered to be a satellite of the other or I prefer they are "co-orbiting" the sun. As the moon is slightly larger than Pluto, until Pluto lost its status as a planet, I would even say "a co-orbiting planet pair."

It is with a great deal of egotism and considerable error to think that the moon orbits the Earth. What actually happens is that the moon's "wobble" takes it closer to the sun than the CoM orbit when the Earth's "wobble" takes it further from the sun and conversely.

From our Earth based POV, the sun appears to be going around the Earth. Fortunately, after a long (~500 year) effort, most people who have been to school for at least a few years have learned this is false.

From our Earth based POV, the moon appears to be going around the Earth. Unfortunately, it will probably also take another 500 year effort, even for most people who have been to college to learn that this is also false.

Both these false primative beliefs ("moon goes around the Earth" and "sun goes around the Earth") are caused by viewing the moving body (sun or moon) from a moving platform. Most of the "Sun going around the Earth" is dye to the spin of the Earth, but even if the Earth were not spinning uneducated people would still hold the view that the sun goes around the Earth once each day. (The day for the nonrotating Earth is about 8766 hours long.)

If Earth were replaced by a tennis ball, the orbit of the moon would not noticably change if view from Mars, etc. I began my correction posts to at least show that the moon would not go flying off into space, etc which was the common POV of this thread. In that it seems I have succeeded, but I guess it is too much to expect to convenience others posting here that the moon does NOT orbit the Earth but, instead co-orbits the sun with the Earth.

Like a primative man viewing the sun go around the Earth, the posters here see the moon going around the Earth and their belief that it actually does so is too hard to change.

Ok. But the CoM is still inside Earth right?

I think so. Barycenter ~4725km from Earth center if I didn't blow the math. (moon mass 0.0123 of earth mass, earth-moon distance 384400km)

The view I prefer is that the Earth/Moon system is unique in the solar system. It is a twin or binary planet. ET astronomers would almost certainly classify it as such.

What is the difference anyway? Consider an average planet and a pen orbiting it. However small pen's mass is, the barycenter is still not exactly the planet's center right? So I think the logical classification would be just by the distance between the barycenter and the center of the bigger object, without mentioning "binary planet" or "sattellite" at all.

If the sun pulls on the moon, why doesn't it rotate. We do.

If the sun pulls on the moon, why doesn't it rotate. We do.First, the moon does rotate, one 360 degree turn each moon month (~28 days). (Moon keeps the same side facing Earth. At full moon this side is pointing at the sun and about 14 days later towards deep space exactly away from sun. - hence it is rotating. Again humans tend to think it does not rotate because that is what it seems like, but not true.)

Second the sun is not the cause of Earth's rotation. Before the mass which is now Earth fell together under its own gravity, it was sort of a gas cloud.* The possiblity that this gas cloud had zero angular momentum is very improbable and even very slow rotation of this cloud will speed up as the mass becomes more concentrated, just as a slowly rotating ice scatter speeds up the rotation rate by bring out streched arms into her side.

No one is completely sure where the moon comes from,** probably was torn from Earth during near miss by passing "Earth size" or large mass (or by direct hit by smaller than Earth mass, (but it was most likely a "glancing blow"). In any case, moon had little rotation and the fact that its mass is not exactly uniform spherically means that the lower energy state is to keep the more massive side turned towards earth.
------------------------
*Probably streched out in long section about 1 AU from sun, perhaps this long section went all the way around the sun in orbit.
**If you "turn time backwards" - Calculate the separation between Earth and moon for earlier date.*** - you find that the moon was once so close to Earth that the strengty of gravity on one side was sufficiently greater than on the other, more distant side. There is a point back in time where this differential pull on the near and far sides is too strong for the tensile strength of rocks. I.e. the Moon would be ripped apart by the gravitational gradient. Thus we know that the moon has not been here as long as Earth has. I.e. We know that Earth got its moon later, but exactly how is still open to debate.

***Days are slowing getting longer as rotational energy disipates in the tides. Exactly how fast, even knowing the shape of the oceans is not easy and much harder as you go back to time when there was only one land mass. Some of the best data comes from old Chinese records of where on Earth total solar eclipses were seen. If you neglect the fact that the spin rate of Earth is changing and calculate where the 3000 year ago eclipse was total you will find that that that village did not see it, one hundreds of miles away did. - Thus we know quite accureately the CURRTENT rate of slowing of the Earth's rotation.

First, the moon does rotate, one 360 degree turn each moon month (~28 days). (Moon keeps the same side facing Earth. ...

I don't understand. If the same side is always facing earth, how is it rotating?

I don't understand. If the same side is always facing earth, how is it rotating?

It rotates around (roughly) the Earth's axis, rather than its own.

I don't understand. If the same side is always facing earth, how is it rotating?DID YOU NOT READ (in last post)

"...At full moon this {Earth pointing} side is pointing at the sun and about 14 days later towards deep space exactly away from sun. - hence it is rotating. Again humans tend to think it does not rotate because that is what it seems like, but not true ..."

It rotates around (roughly) the Earth's axis, rather than its own.This POV is also strongly influnced by fact you live on Earth. In fact the moon is on nearly perfect ellipse, but one that has slighth wobbles. In about 14 days these wobbles take the moon from its closer to sun diviation from the ellipse to it most distant point from the sun. In 14 days it rotates thru 180 degrees. It is true that this locking of the wobble period and rotational rate was caused by the Earth's gravity, but it does represent angular momentum and would continue to be one 360 degree rotation EVEN IF THE EARTH NO LONGER EXISTED. Surely one should thus not say it is rotating about the point where the Earth was, if Earth did noty exist. Why say that now when the Earth does exist?

Fact is that moon rotates 360 in ~28 days, regardless of where you wish to consider the "center of ortation." I prefer to think of moon as rotating about its own center of mass as it orbits the sun, as anyone who did not live on Earth surely would.

It rotates around (roughly) the Earth's axis, rather than its own.

why doesn't it rotate around its own axis?

Fact is that moon rotates 360 in ~28 days, regardless of where you wish to consider the "center of ortation." I prefer to think of moon as rotating about its own center of mass as it orbits the sun, as anyone who did not live on Earth surely would.
It also rotates about the common centre of gravity of the Earth-moon system (which is several km below the Earth's surface - roughly 1/81 of the distance from the centre of the Earth to the Centre of the moon).
If the Earth disappeared where would the C of G of the "system" be then?


why doesn't it rotate around its own axis?
Tidal locking:
http://en.wikipedia.org/wiki/Tidal_locking

It also rotates about the common centre of gravity of the Earth-moon system (which is several km below the Earth's surface - roughly 1/81 of the distance from the centre of the Earth to the Centre of the moon). If the Earth disappeared where would the C of G of the "system" be then?... I think the motion around the Center of Mass, CoM, should be called "orbits" not "rotates." This motion is a circle. The moon has a circular path about the CoM and as it goes around, it spins or rotates once each orbit.
This is the way we describe the motion of the planets. They "orbit" about the sun (go around it) and spin or "rotate" about their own axis. It is confusing to reverse the use / meaning of these terms only for the case of the moon.

I am not sure, but think Mercury does this also. I.e. it orbits the sun and spins or rotates once in each orbit (or perhaps it is 1.5 times in each orbit - I forget)

In answer to your final question: Deep inside the moon, but not exactly at its volume center.

later by edit (after looking at your wiki link):

My use of these terms is the standard, not yours. For example, your wiki link states:
"... A tidally locked body takes just as long to rotate around its own axis as it does to revolve around its partner. ..." I.e. one 360 spin or rotation per orbit.

I don't understand. If the same side is always facing earth, how is it rotating?

Try this:

Take two coins of the same size. Place them on a table, touching each other. Now, hold one of them in place with your finger (that's the Earth) and roll the other one around the first one with your other hand (that's the Moon).

Notice which way the rolling coin faces as it goes around. Look at which way it faces compared to the centre of the Earth, and compared to a fixed point somewhere else on the table.

A theory of expanding space needs a really good explanation why space cannot expand within solar space. I will accept the idea provisionally if someone claims to have calculated it out with some degree of certainty, but even the idea that space has stretched since the moment of creation is not certain.

On the other hand a sane and reasonable person could hypothesize that the pulls of the various planets and stars can stretch out space over time. It it is elastic that is how it is pulled on.

A theory of expanding space needs a really good explanation why space cannot expand within solar space. I will accept the idea provisionally if someone claims to have calculated it out with some degree of certainty, but even the idea that space has stretched since the moment of creation is not certain.

On the other hand a sane and reasonable person could hypothesize that the pulls of the various planets and stars can stretch out space over time. It it is elastic that is how it is pulled on.

Space overall can get bigger and the distance between galaxy clusters grow and grow, but small objects held together by gravity, like the Earth and moon, Earth and sun, all stars in this one galaxy, the few galaxys in out local group - stay the same distance apart. If you put 2 rocks on an elastic sheet and tied them together with string, they would stay at the same separation even when the sheet is stretched. Thats not hard to grasp, right?

I think so. Barycenter ~4725km from Earth center if I didn't blow the math. (moon mass 0.0123 of earth mass, earth-moon distance 384400km)

The view I prefer is that the Earth/Moon system is unique in the solar system. It is a twin or binary planet. ET astronomers would almost certainly classify it as such.

I think that if the barycentre is still inside Earth though not at its core, the moon can still be called our satelite because it orbits a point within the Earth. If the moon was 2 or 3 times heavier the barycentre would be OUTSIDE Earth, and both bodys would orbit a point in space between them. Then you could call us a binary planet. Isnt Pluto and Caron like that?

Space overall can get bigger and the distance between galaxy clusters grow and grow, but small objects held together by gravity, like the Earth and moon, Earth and sun, all stars in this one galaxy, the few galaxys in out local group - stay the same distance apart. If you put 2 rocks on an elastic sheet and tied them together with string, they would stay at the same separation even when the sheet is stretched. Thats not hard to grasp, right?



Over time the sheet might stretch, the way that a pair of blue jeans gets loser as you wear it. That's not too hard to grasp, is it?

actually the earth is getting further and further away from the sun because the sun is losing mass (due to the solar wind)
if you think that's insignificant take in account that the sun has shined for around 5 billion years and that it already has lost abouth a 100 earth masses and proberly will lose a equal amount before it goes to it's second stage.
Then again the earth has also have a natural cycle in wich it's migrates a bit.

http://en.wikipedia.org/wiki/Sun#Life_cycle

The sun already has greater gravitational effect (stronger force) on the moon than the Earth does.
Would you like to show us the math you are using, Billy T ?

Seems to me that if the Sun's gravity were stronger than the Earth's, the Moon would always have the same side turned towards the Sun.

Would you like to show us the math you are using, Billy T ?

Seems to me that if the Sun's gravity were stronger than the Earth's, the Moon would always have the same side turned towards the Sun.

If the same side is always pointing towards the Earth, wouldn't the same side always be pointed towards the sun?

If the same side is always pointing towards the Earth, wouldn't the same side always be pointed towards the sun?
Hard to follow your mental processes, Orleander!
When the same side is facing the Sun as is facing the Earth is when we see a Full Moon.

Hard to follow your mental processes, Orleander!
When the same side is facing the Sun as is facing the Earth is when we see a Full Moon.

sorry, I confuse easily. :o lol
I'm still not understanding all this, so I kinda gave up.

Are meteors still hitting the moon?

sorry, I confuse easily. :o lol
I'm still not understanding all this, so I kinda gave up.

Are meteors still hitting the moon?

Naw. The Moon has been in its present orbit for over 4 billion years. The meteors have learned to go around.

That is very interesting. So the Moon can have its own sattellite, and that one having own tiny sattellite and so on.

There is a limit, of course. http://en.wikipedia.org/wiki/Hill_sphere#Further_examples
An astronaut could not orbit the Space Shuttle (mass = 104 tonnes), where the orbit is 300 km above the Earth, since the Hill sphere is only 120 cm in radius, much smaller than the shuttle itself.

Lunar orbits are problematic not only because of the Moon's relatively weak gravity but also because of the Moon's lumpy gravity. The orbit of PFS-2 about the moon is particularly bizarre. http://science.nasa.gov/headlines/y2006/06nov_loworbit.htm
The orbit of PFS-2 rapidly changed shape and distance from the Moon. In 2-1/2 weeks the satellite was swooping to within a hair-raising 6 miles (10 km) of the lunar surface at closest approach. As the orbit kept changing, PFS-2 backed off again, until it seemed to be a safe 30 miles away. But not for long: inexorably, the subsatellite's orbit carried it back toward the Moon. And on May 29, 1972—only 35 days and 425 orbits after its release—PFS-2 crashed.

It is with a great deal of egotism and considerable error to think that the moon orbits the Earth. What actually happens is that the moon's "wobble" takes it closer to the sun than the CoM orbit when the Earth's "wobble" takes it further from the sun and conversely.

This is merely bad logic. The same bad logic applies to most moons, including Pluto and Charon. The same bad logic applies to our orbit about the galaxy (we aren't orbiting the sun!) It is not geocentricism that makes us think the Moon is a satellite of the Earth. It is math and physics. Astronomers use the Hill sphere as the metric for determining whether some body is a bound satellite of a some other object that is orbiting the Sun. They use the location of the barycenter to distinguish between satellites and double planets. If the moon were not a satellite of the Earth it would behave more like 2002 AA29 (http://neo.jpl.nasa.gov/2002aa29/2002aa29.gif).

If the same side is always pointing towards the Earth, wouldn't the same side always be pointed towards the sun?The moon is in synchronous orbit around the earth but all of its surface still gets lit by the sun(so faces the sun) thats why we get half moons, quarter moons, full moons etc... despite us basically only being able to see one face of the moon from our earthly home.

Over time the sheet might stretch, the way that a pair of blue jeans gets loser as you wear it. That's not too hard to grasp, is it?

No, coz thats just what I was saying myself mate. The sheet may stretch, but the rocks sat on dont move away from each other if theyre tied together!

Seems to me that if the Sun's gravity were stronger than the Earth's, the Moon would always have the same side turned towards the Sun.

The lock on the moon's rotation was done by TIDES, not gravity total. Tides are caused by the pull on 1 side of the moon being stronger than on the other side - the more the diference, the more the tide. The sun's gravity is so strong and the moon (and Earth) are so far from it that the diference felt across teh moon's width is tiny. But the moon is lots closer to Earth, and Earth's gravity drops off much faster than the sun's. So the diference, and tide, caused by Earth is much stronger, though the total gravity is less.

Its the same reason why the moon causes bigger tides on Earth than the sun, although the moons gravity is much weaker . If the moon's pull on all parts of Earth was the same, it would cause no tides at all.

...The lock on the moon's rotation was done by TIDES, not gravity total. Tides are caused by the pull on 1 side of the moon being stronger than on the other side - the more the diference, the more the tide. The sun's gravity is so strong and the moon (and Earth) are so far from it that the diference felt across teh moon's width is tiny. But the moon is lots closer to Earth, and Earth's gravity drops off much faster than the sun's. So the diference, and tide, caused by Earth is much stronger, though the total gravity is less.
Its the same reason why the moon causes bigger tides on Earth than the sun, although the moons gravity is much weaker . If the moon's pull on all parts of Earth was the same, it would cause no tides at all.

You are correct. I can only add: Gravity falls off as the inverse square (of separation between mass centers) and the gradient og gravity (tide producer) as the inverse cube.

You are correct. I can only add: Gravity falls off as the inverse square (of separation between mass centers) and the gradient og gravity (tide producer) as the inverse cube.

Which means: if the Moon were twice as far from Earth as it is, its tides would be only one eighth of their current strength. The Solar tides would then be the stronger, and there woulld be no ambiguity among us forumites about which body exerts the most gravity on our globe.

I wonder what the ocean tides on Earth were like in the distant past, when the Moon was much closer (and the Earth's rotation faster?)

I wonder what the ocean tides on Earth were like in the distant past, when the Moon was much closer (and the Earth's rotation faster?)weel, for one thing it wasn't safe to go down to to the beach unless you were amphibious.

Correct. At the point where other planets' and Sun's influence on the moon becomes stronger than that of Earth on the moon, the moon will become a minor planet of the solar system or it will be ejected from the solar system.

This would never happen, and not just because the Sun will expand into a red giant and likely envelop the Earth before it can occur.

Assuming that such a fate is avoided, the following would happen:

The moon will continue to recede from the Earth and the Earth will continue to slow its rate of rotation.

Eventually, the period of the Moon's orbit and the Earth's rotation will match, and the Earth will present the same to the Moon, just as the Moon presents the same face to us. at this point the moon will stop receding. (it was the difference between the two periods that caused the transfer of angular momentum, that led to the recession)

If these were the only two bodies we had to consider, this would be the final stable configeration, but it isn't.

The Sun also exerts an tidal influnence on the Earth, and will continue to slow the Earth's rotation so that it will become tidally locked with the Sun.

As the Earth begins to slow in its rotation, the Moon will now orbit in a shorter period than the Earth rotates. Once again there will be a difference between the Moon's orbital period and the Earth's rotational period, which sets up a new tidal interaction.

Under these new conditions(moon faster, Earth slower), the moon will start to approach the Earth rather than recede. It will continue to move in, orbiting closer and closer to the Earth, until it passes the Roche limit and is torn apart by tidal forces.

Earth becomes a ringed world.

This would take billions upon billions of years to occur, and as I said, the Earth and Moon aren't likely to last that long. In fact, I do believe that the Sun is due to swell to red giant stage before the Earth can even become tidally locked to the Moon.

Which means: if the Moon were twice as far from Earth as it is, its tides would be only one eighth of their current strength. The Solar tides would then be the stronger, and there woulld be no ambiguity among us forumites about which body exerts the most gravity on our globe.

I wonder what the ocean tides on Earth were like in the distant past, when the Moon was much closer (and the Earth's rotation faster?)I have read that the open ocean tides may have been much higher.

You are correct about the 1/8 th amplitude of the open ocean tides but those near shore and in inlets are more complex. I do not know if the 1/8 tide is less than that of the sun.

The Solar tides are roughly 1/3 the strength of the Lunar (in modern times).

Under these new conditions(moon faster, Earth slower), the moon will start to approach the Earth rather than recede. It will continue to move in, orbiting closer and closer to the Earth, until it passes the Roche limit and is torn apart by tidal forces.

Earth becomes a ringed world.

If, as you said, Earth & Moon survive the Sun's red giant phase, the timeframe for the Moon's final suicidal approach to Earth would be around 30-40 billion years. Of course, they may survive by moving further away from the Sun as it sheds mass in the form of a planetary nebula, weakening its gravitational field - this in turn will reduce the tidal effect it exerts, and hence stretch out the fate of Earth & Moon still longer.

By the time Earth finally has a ring system, the white dwarf Sun will almost certainly have faded to black and will be unable to illuminate the rings. A pity.

A long time ago our Earth was a moon and our Moon was like the earth. When the Ancient Earth (the current moon) died, it gave all its energy to its child which grew into this planet we call Earth. That's why the moon is so old and dead now.

Let me insert this point, if we base the effect of the moon on the earth, that of the moon and earth which we can measure, and assume our current given mass and density. The same determinations for the Suns effect on the earth and moon would give the the result that both the Earth and Moon should not move at all in rotation, and they should behave within our solar system as the planets Venus and Mercury, having only a revolution around the sun.

Without doubt the earth was larger in history and for that reason the moon was closer to the earth, the moon can get as close as 6500 miles(9000?) from the surface of the earth at which point it begins to break apart, lunar surface crust starts to uplift (having constant motion).
It appears that the earth shrinks every 8,000 to 13,000 years, as a result of magnetic pole reversal events, a estimated 12 to 25 miles is the amount of shrinkage per radius. of which gravity becomes more focused, resulting in more stationary events of kinetic energy (slower). earth prior had a more dense atmosphere, at one time exstending to the 9,000 mile mark in altitude currently called the hydrogensphere? existing from 4,000 miles to 9,000 miles with end tails to 16,000 miles.
It may appear that with enough time in history that the moon was actually joined with the earths atmosphere and formed a spot within the earths larger atmosphere looking simular to jupiters red spot. the time at which this would occur in earth history is a guess right know as the distrubance of the moons orbit with each magnetic reversal is a guess, but it appears that at one time the earths magnetic feild envolped the moon, given the smooth face that we see when we look at it (the face you see from earth.) the face of the moon defines that the earth was closer to the moon at that the moon had a different motion.
The event that the moon and earth shared the same atmosphere,creates a possiblity that life may have began on the moon before decending to earth, this exist as the earth does have more gravition effect on the moon than the moon has on the earth,( it is i belive currently held that virus and and bacteria can culture on the moon).


DwayneD.L.Rabon

Let me insert this point, if we base the effect of the moon on the earth, that of the moon and earth which we can measure, and assume our current given mass and density. The same determinations for the Suns effect on the earth and moon would give the the result that both the Earth and Moon should not move at all in rotation, and they should behave within our solar system as the planets Venus and Mercury, having only a revolution around the sun.

Without doubt the earth was larger in history and for that reason the moon was closer to the earth, the moon can get as close as 6500 miles(9000?) from the surface of the earth at which point it begins to break apart, lunar surface crust starts to uplift (having constant motion).
It appears that the earth shrinks every 8,000 to 13,000 years, as a result of magnetic pole reversal events, a estimated 12 to 25 miles is the amount of shrinkage per radius. of which gravity becomes more focused, resulting in more stationary events of kinetic energy (slower). earth prior had a more dense atmosphere, at one time exstending to the 9,000 mile mark in altitude currently called the hydrogensphere? existing from 4,000 miles to 9,000 miles with end tails to 16,000 miles.
It may appear that with enough time in history that the moon was actually joined with the earths atmosphere and formed a spot within the earths larger atmosphere looking simular to jupiters red spot. the time at which this would occur in earth history is a guess right know as the distrubance of the moons orbit with each magnetic reversal is a guess, but it appears that at one time the earths magnetic feild envolped the moon, given the smooth face that we see when we look at it (the face you see from earth.) the face of the moon defines that the earth was closer to the moon at that the moon had a different motion.
The event that the moon and earth shared the same atmosphere,creates a possiblity that life may have began on the moon before decending to earth, this exist as the earth does have more gravition effect on the moon than the moon has on the earth,( it is i belive currently held that virus and and bacteria can culture on the moon).


DwayneD.L.Rabon

Wow! That's about the worst "science" I've ever read!! Almost pure fiction and hardly a word of truth anywhere in it. The Earth does not loose mass as a result of the magnetic poles flipping. Neither was it ever larger than today (except for possibly just before the collision that formed the Moon) and in fact, it gains mass every singe day of it's existence due to all the space debris that is constantly raining down.

That post is nothing but nonsensical, unsupported blather. :bugeye:

If the Moon was inside Earth's atmosphere, wouldn't it fall on Earth because of air friction?

Let me insert this point, if we base the effect of the moon on the earth, that of the moon and earth which we can measure, and assume our current given mass and density. The same determinations for the Suns effect on the earth and moon would give the the result that both the Earth and Moon should not move at all in rotation, and they should behave within our solar system as the planets Venus and Mercury, having only a revolution around the sun.


DwayneD.L.Rabon

Neither Mercury or Venus keeps the same face to the Sun( And even if they did, it wouldn't mean that they had no rotation, but that their rotational periods equaled their orbital periods.)
Mercury has a orbital period of 87.97 days and a rotational period of 58.6 days. This means that it has a mean Solar "day"(noon to noon) of 175.52 days.
Venus has a oribital period of 224.70 days and a retrograde rotational period of 243 days. This gives it a solar "day" of 116.75 days.

You're supposed to ignore the science and just believe the woowooism, Temur.

You're supposed to ignore the science and just believe the woowooism, Temur.


I LOVE the woowooism!!! :worship:

Neither Mercury or Venus keeps the same face to the Sun( And even if they did, it wouldn't mean that they had no rotation, but that their rotational periods equaled their orbital periods.)
Mercury has a orbital period of 87.97 days and a rotational period of 58.6 days. This means that it has a mean Solar "day"(noon to noon) of 175.52 days.
Venus has a oribital period of 224.70 days and a retrograde rotational period of 243 days. This gives it a solar "day" of 116.75 days.

Janus, I've no idea where he gets his "facts" - it appears that he just makes them up as he goes along. But the really sad thing is that once he's come up with them, he seems to truly believe they are accurate!

I've no idea where he gets his "facts" - it appears that he just makes them up as he goes along. But the really sad thing is that once he's come up with them, he seems to truly believe they are accurate!

Dwayne DL Rabon has been a notorious purveyor of psuedo-scientific garbage for years. One could say he's either boldy challenging the established view - or just making up nonsense for the fun of it. I think the latter.

If the Moon was inside Earth's atmosphere, wouldn't it fall on Earth because of air friction?

The Moon would break up long before it got close enough to Earth for the atmosphere to be significant.

...The Moon would break up long before it got close enough to Earth for the atmosphere to be significant.

how close would it have to be before it broke?

This is determined by something called the Roche Limit. (http://en.wikipedia.org/wiki/Roche_limit)
For the moon this is about 9500 km.

Well, the earth loses the surrounding atmosphere with each magnetic pole reversal, which results in a loss of mass. The prior larger earth in history having a larger atmosphere and appearantly denser atmosphere resulted in a a much less denser surface crust, a belive that a prior atmosphere that exstended to the 9,000 mile to 16,000 mile mark would exspand causing fluid motion for about 2000 miles?, the current atmosphere and ocean bodies move the earth across 23 degrees( haveing that much gravitional force in motion,being a pivot). the gravitional force of the oceans in total is enough to controll the motion of the moon.
So in a prior earth with a larger diameter as a result of atmosphere we find both sediment and water in greater abundance in the atmosphere, trace elements found in the upper atmosphere are a good indicator of what may have been the compnets of the atmopshere at the time, with a larger volume of helium. in general the current surface of the earth would be exspanded and less dense this would cause for a wider motion of the moon but a slower motion i susspect, eventually the moon may become near stationary in appearance from space floating on the earths atmosphere while the actuall heavier mass of the earth spins faster at the center of the earth.
the moon is actually 1/89th the mass of the earth which is less than that of the earths nuclear magnetic feild, and earths normal magnetic feild is many times stronger about 1250 times stronger, so even the current magnetic feild of earth could controll the mtion of the moon, actually float the moon much simular to a magnet floating on another magnet.
a larger earth would have a stronger magnetic feild and stronger nuclear feild making hold the moon in a earth atmosphere childs play. that of complete ease.

with each magnetic reversal the magnetic feild is lost for a given time frame and in that time the earths atmophere burns off and is blasted in to upper earth atmophere, as a result of the ionzation caused by the magnetic feild when it falls through the atmosphere, creating a hot plasma, that is ejected by lower mass that erupts from the denser mass of the earth ionzing from the same magnetic fall, in additon the suns solar radiation burns off earth atmophere.
the magnetic feild also supports lift of common dirt as every thing on earth is polarized by the magnetic feild with the loss of the magnetic feild so also is the loss of that polar support and the earths mass collaspes causing the earth to shrink.
lastly in the prior earth , a larger earth it actuall appears that mars may have been a moon of earth, the earth having to moons both mars and our current moon.
as for the solar system it appears in some calculations that most of the gas giants have a internal bodies, two bodies that orbit each other at thier center. on which will in end become a orbiting moon as that of the earth and moon.

DwayneD.L.Rabon

Dwayne, I mean really, would you just shove off, or stop talking nonsense. You are trying my patience.

I do note that your name is an anagram of " Wander on badly." I tend to think that says it all.

Dwayne DL Rabon has been a notorious purveyor of psuedo-scientific garbage for years. One could say he's either boldy challenging the established view - or just making up nonsense for the fun of it. I think the latter.


Yes, while I was still in my initial read-only mode, I saw several dozen of his purely nonsense posts. In fact, as I recall, pretty much ever single one of them was like a child babbling.

I wish you were correct in your assessment but I'm afraid it's not accurate. He has an unhealthy obsession with numbers (especially big ones) and frequently (for him) sticks pretty closely to a few subjects that he seems to think he understands - though as you say, it's just pseudo-scientific garbage. Things like the pole reversals (as he's launched into yet again here) being the cause of mass extinctions, that the temperature at the Earth's core is near absolute zero (!!) and a few other choice topics.

I also remember him calling himself an absolute genius more than once. And bragging that he was home-schooled (tutored) by a high-ranking military officer - a colonel, I believe the claim was. All in all, I'm afraid (sadly so) that he actually believes all the junk he posts here. I must say that I had difficulty accepting that at first but he finally convinced me.

All in all, I'm afraid (sadly so) that he actually believes all the junk he posts here. I must say that I had difficulty accepting that at first but he finally convinced me.

A certifiable nutcase then. Poor fellow (or is "he" female?)

Incredible after all these years, Dwayne's universe is still mixed up with ours.

Yeah I guess so, seems that thier are a few missing screws with several people on the forms: and as i recall the you three have never provide any argument other that slander comments, although i have sought each of out for your argument. it seems there that several of you have quite a imagination, spout of the mouth, or keyboard.

I have to assume that the common taught in the USA is not the common taught where where you dwell.

Still more than interested in your arguments, please mind i won't be hood winked like your employers, can't loaf for your pay check and daily bread with Old Dwayne, my fellow earthlings

DwayneD.L.Rabon

Dwayne,
you're falling to pieces. There were no esoteric numbers in that post, although you still managed to be largely unintelligible.
You have never visibly sought anyone out for an argument, as you put it. You have merely regurgitated more numeric bile when challenged on your first mathematical expectoration.
Fact: either you are mentally imbalanced, in which case I urge you to seek professional help immediately. Or, you a very large troll in which case you deserve all the ridicule and contempt which is heaped upon you.

Let us know which of the two categories applies, please.

Did the moon have grass? maybe a few less potholes.

what do you mean?

Let's Start A fresh!!

What about the event of life starting on the moon, confuses you.
Simply the gravity of the earth is greater than the moon, this defines that a smaller life form one less than two pound could have formed on the moon,prior to life on earth.
Is not the moon in the so called life Zone of our solar system.
Sure enough it would seem rather odd to say life started on the moon with out some exsplaination, and so, as it appears the earth was once much larger than it is today, assumably it was as large as jupiter its self, of which the moon may have taken its orginal formation, given the assement of soil samples ectra that are declared the same age and near compostion as earth.
it would only follow to reason that the moon was within the physical enviroment of the larger past earth, assuming that such a prior earth body was mostly gaseous, simply the moon would float in such a enviroment of atmosphere. considering a density of 1 or higher as that of jupiter. life in such a case could there for exist on the moon, and in earths case orginate from there, in calculation i found a seperation of the moon from the earth atmosphere at about 10,000 miles, Earth radius 10,000 miles, this event would have occured some 248,000 years ago, where the earths terristal density was about 2.8.
Given the gravity of earth being higher it is more lilky that earth would premote life on the moon before the moon premote life on the earth, thats simple logic.

DwayneD.L.Rabon

If Earth was so big what is the reason for it to become small as it is today?

If Earth was so big what is the reason for it to become small as it is today?

It wasn't, of course. That's just more of his rambling nonsense. Not long ago, I read on NASA's website (and I've seen it in other places as well) that the Earth actually gains mass every single day from the space debris that rains down on us. In other words, it's NEVER been larger than it is right now - and it will be slightly bigger tomorrow. :)

Repeative magnetic pole reversals. like 50 of them or something like that.


DwayneD.L.Rabon

will the moon erode away?

I was wondering if only Americans had been on the moon. I read that the Russians made several hard landings and soft landings. What's the difference?

What's the difference? The Russians landed automated machines, not people.

what's the difference between hard landings and soft landings? We made them too.

what's the difference between hard landings and soft landings?

Hard landings are a euphemism for crash landings. The earliest Moon probes, like the Ranger series, simply kept transmitting pictures until they impacted on the surface. The technology to decelerate in a vacuum, and land intact, either didn't exist or was uneconomical at the time.

Soft landings, of course, were essential in the Lunokhod and Apollo programs.

Did the moon have grass? maybe a few less potholes.

Writers used to assume that the Moon originally had an atmosphere and hydrosphere, which were lost to space due to its low escape velocity - in that case, life could perhaps have got started there, including vegetation (and might still exist, in some unimaginably hardy and insulated form, perhaps tapping underground pockets of gas and water...)

However, rock samples returned from the Moon show virtually no volatiles, including water. If the current theory of Lunar formation via a giant protoplanetary collision with Earth is correct, then very little water or gases would have been incorporated into the yong Moon - such light compounds would have simply dispersed in space, not accreted. Our poor Moon was probably airless, waterless and lifeless right from the start. :bawl:

Let's Start A fresh!!

What about the event of life starting on the moon, confuses you.
Simply the gravity of the earth is greater than the moon, this defines that a smaller life form one less than two pound could have formed on the moon,prior to life on earth.
Is not the moon in the so called life Zone of our solar system.
Sure enough it would seem rather odd to say life started on the moon with out some exsplaination, and so, as it appears the earth was once much larger than it is today, assumably it was as large as jupiter its self, of which the moon may have taken its orginal formation, given the assement of soil samples ectra that are declared the same age and near compostion as earth.
it would only follow to reason that the moon was within the physical enviroment of the larger past earth, assuming that such a prior earth body was mostly gaseous, simply the moon would float in such a enviroment of atmosphere. considering a density of 1 or higher as that of jupiter. life in such a case could there for exist on the moon, and in earths case orginate from there, in calculation i found a seperation of the moon from the earth atmosphere at about 10,000 miles, Earth radius 10,000 miles, this event would have occured some 248,000 years ago, where the earths terristal density was about 2.8.
Given the gravity of earth being higher it is more lilky that earth would premote life on the moon before the moon premote life on the earth, thats simple logic.

DwayneD.L.Rabon

"Fresh", nothing! Just more Rabon nonsense. :bugeye:

However, rock samples returned from the Moon show virtually no volatiles, including water. If the current theory of Lunar formation via a giant protoplanetary collision with Earth is correct, then very little water or gases would have been incorporated into the yong Moon - such light compounds would have simply dispersed in space, not accreted. Our poor Moon was probably airless, waterless and lifeless right from the start. :bawl:

:bawl::bawl:

The Moon acts as a precise measurement of the truths of astrology. I dont think I need to say more because they are well documented.:)

Temur is correct in his last post. We will not loose the moon. But it's orbit will stabilize and we will loose our tides and our rotation. But by that time, the Earth will unhabitabal as the sun will have expanded and gotten hotter, making life on Earth rather uncomfortable.

Is the moon shaped like a pear? Seems like with one side always facing us, that side we pull on would get pulled out a bit.

You mean tidal effect?

You know, I think Orleander is a very smart lass and she knows well how much of a slave we men are to testostrone.

You mean tidal effect?

I don't know.
OK, our moon doesn't spin on its own axis because the gravitational pull of the earth is so strong, right? Why then would the moon develop into a sphere and not a pear shape? Wouldn't the gravitaional pull of the moon pull it more to one side....our side?

You know, I think Orleander is a very smart lass and she knows well how much of a slave we men are to testostrone.

what?
<giggle>

I don't know.
OK, our moon doesn't spin on its own axis because the gravitational pull of the earth is so strong, right?
First of all, the Moon does spin on its own axis, At a rate of 1 rotation per orbit around the Earth. (This leads tot he fact that the Moon does not keep the exact same face pointing towards the Earth at all times. The Moon's orbit is slightly eccentric, meaning that it changes distance from the Earth during its orbit. When it it nearer the Earth it orbits slighty faster than when it is further. OTOH, the Moons rate of spin is constant. So at times the spin lags behind the orbit and at time it speeds ahead. From Earth this makes the Moon appear to rock back and forth on its axis and brings a part of the "farside" of the moon into view over the course of a orbit. This rocking back and forth is called "Libration".

Why then would the moon develop into a sphere and not a pear shape? Wouldn't the gravitaional pull of the moon pull it more to one side....our side?

Any shape the Moon finally settled on happened when it was younger and hadn't solidified yet.

The Moon does have bulge, but it is on the farside, and apparently formed when the Moon was "softer" and had a more eccentric orbit.

The Moon did not always rotate with the same period as it orbited as it does now. Some models show that this bulge could have formed during a time when it rotated at a rate of three rotations per 2 orbits.

First of all, the Moon does spin on its own axis, At a rate of 1 rotation per orbit around the Earth. (This leads tot he fact that the Moon does not keep the exact same face pointing towards the Earth at all times. ....

AURGH!! I'm still not getting this even after 5 pages.
WTHell is the dark side of the moon then and if the moon does rotate why do we never see it?

Check out these image, it is looking down on the moon's orbit from above:

http://home.earthlink.net/~parvey/sitebuildercontent/sitebuilderpictures/orbit4.gif

The top pic is of the situation as it exists with the Moon. Note that that in order for the moon to keep one face to the Earth, it must turn as it orbits.

The second pic is what would happen if the moon didn't rotate. Note that in this case, the Moon does not keep the same face to the Earth at all times.

There is no "dark side" of the Moon, there is a "far side" of the Moon. That side which never faces the Earth.

I give up. I am just too stupid. I don't see how the moon can turn and yet we never see the far side.

Hello Qrleander

Attach a string to a ball. Swing it around your head. The point on the ball where the string is attached always faces you. Someone standing out of the way would see the ball rotating as well as orbiting you.

:)

Imagine you are dancing wals with somebody. Then you don't see his back but he will be spinning, or in other words, he can see every wall of the room as he rotates right?

Orleander, the reason is in the synchronization of orbit and spin/rotation. Here is an experiment to explain it, take a pen that has some writing on the side. Put it at the far end of you peripheral vision. Place the written material so that it is at a ninety degree angle to your line of site. At this point, the writing should not be visible to you. Now slowly move your extended hand holding the pen so that it is directly in front of you. You will notice that you are now able to read the writing on the pen. You did not move, the pen did not rotate, and you are seeing a different face of the pen because your perspective has changed. In order for you to see the same face of the moon the moon needs to rotate.

Ps I still think you are an extremely intelligent lass!

In order for you to see the same face of the pen, the pen would need to rotate as it moves around you.

I give up. I am just too stupid. I don't see how the moon can turn and yet we never see the far side.

Okay, try this. In the following animation I shaded the "planet" red and white and it rotates at the same rate as the "moon" orbits. Note that the white side of both the moon and planet always face in the same direction. It is obvious that the planet rotates, and if the moon always faces in the same direction as the planet, then the moon must also rotate as it makes its trip around the planet, even though it always keeps one face towards the planet. In fact, it must rotate in order to keep the same side towards the planet.

http://home.earthlink.net/~parvey/sitebuildercontent/sitebuilderpictures/orbitanim.gif

Okay, try this. In the following animation I shaded the "planet" red and white and it rotates at the same rate as the "moon" orbits. Note that the white side of both the moon and planet always face in the same direction. It is obvious that the planet rotates, and if the moon always faces in the same direction as the planet, then the moon must also rotate as it makes its trip around the planet, even though it always keeps one face towards the planet. In fact, it must rotate in order to keep the same side towards the planet.

http://home.earthlink.net/~parvey/sitebuildercontent/sitebuilderpictures/orbitanim.gif

Nice one, if you cant understand it from that animation you really are hopeless.

Nice one, if you cant understand it from that animation you really are hopeless.As an old teacher, I seldom give up on a "Hopeless Student."

Now imagine that the "moon" in the animation is slowing enlarging until it is equal to the "Earth" and both orbit their common mass center. Which one is not rotating? The moon? Ok, then change the labels on these identical co-orbiting objects so now, with the new labels applied, would you claim the Earth is not rotating?

Earth orbits the sun and also spins on its own axis. This is exactly what the moon does? Does that mean from the sun's point of view we have a far side that is never seen?

The moon rotates around us, but I don't see it spinning on its own axis. If it was a ball of yard attached to the earth, how would it spin on its own axis?

Earth orbits the sun and also spins on its own axis. This is exactly what the moon does?
the difference is that the Earth takes one day to make one rotation and 365 days to orbit the sun, while the moon takes 27.33 days to make one rotation and 27.33 days to make ooen orbit.
Does that mean from the sun's point of view we have a far side that is never seen?
no, because of the above difference in the period of the orbit and the period of the rotation.

The moon rotates around us, but I don't see it spinning on its own axis. If it was a ball of yard attached to the earth, how would it spin on its own axis?

Imagine you were standing on top of the moon in the animation (assuming that in the animation we are looking from "above" the pair looking down.
Now imagine stars in the sky. What would you see. The star would appear to travel in circles around the point straight above your head.

Now, are these stars really moving in circles, or do you see this because the moon you are standing on is spinning?

The problem you are having is that you are judging spin in reference to the line connecting the planet and the moon, when in fact, spin is judged by the stars in the sky.

...The moon rotates around us, but I don't see it spinning on its own axis. ... Perhaps your POV of view / disagreement is not really about the moon rotating but in the phrase "about its own axis." If some object in a box (like the animation box) has its "red side" first aligned or pointing towards "wall 1" and them a little later towards "wall 2" etc. thru walls 3 and 4 until it is again facing wall 1, I think you should agree it must have been rotatating, do you not?

I.e. is your real objection the "about its own axis" part?

If so, we need to be more clear about what is defined as "rotation" and what is defined as "orbiting."

OK, the moon orbits us. Does it have its own axis, like we do? If so, why does Earth only see one side?

OK, the moon orbits us. Does it have its own axis, like we do? If so, why does Earth only see one side?

Yes, it does.

Consider this, Orelander - you are sitting in a chair facing someone who is standing. They move around you in a circle, facing you all the time.

If they did not rotate slowly, you would also see their one side, then their back and then their other side - eventually their face again. So they MUST be turning all the time - though slowly - for you to see ONLY their face all the time. :)

Just to add to what Read-0nly said. Think of the cardinal directions as you do this. The person starts to the East of you and faces West towards you. As he circles you, he has to keep changing the direction he faces in order to keep facing you, so that by the time he is North of you he is facing South, West of you, facing East, and South of you, facing North. He is turning around his own axis facing different directions the whole time.

If he did not turn around his own axis, then he would face West the whole time. Then when he was North of you, you would see his left side. When he was West of you, you would see his back, and when he was South of you, you would see his right side. IOW, you would see every side of him as he circled you.

Conservation of angular momentum (so far as I understand it) means that as a planet's rotation is slowed down by tidal drag--as the Earth is by the moon--the Moon moves further away. 2 inches per year if my information's correct.

Yes, it does.

Consider this, Orelander - you are sitting in a chair facing someone who is standing. They move around you in a circle, facing you all the time.

If they did not rotate slowly, you would also see their one side, then their back and then their other side - eventually their face again. So they MUST be turning all the time - though slowly - for you to see ONLY their face all the time. :)

So if I have a rock on a piece of string and swing it round my head that rock will always have the same face towards me - does that mean it's rotating on its own axis (while anchored by the string)? :D

So if I have a rock on a piece of string and swing it round my head that rock will always have the same face towards me - does that mean it's rotating on its own axis (while anchored by the string)? :D

Yes, because being anchored to the string causes it to.

Now change up the experiment a little. Intead of anchoring the string directly to the rock, let's assume that there is a rod that extends through the center of mass of the rock and exends beyond the ends. You attach your string to this rod by means of a y shaped yoke. (So that if you hang the rock by the string you can spin it freely along an axis perpendicular to the string.

Further assume that there is no friction between the yoke and rod.

If you swing the rock around your head now, the rock will continue to face in the same direction at all times, and will not always have one face towards you. (just as in the example with the person and chair above.) In this situation the rock is free to do as it wants rotation wise.

When the string is anchored to the rock it is forced to keep one side towards you.

Yes, because being anchored to the string causes it to.
Which sort of contradicts your comment about "turning" to keep one face toward the viewer in the centre.
It can't turn on its own axis because the string anchors it.

OK, the moon orbits us. Does it have its own axis, like we do? If so, why does Earth only see one side?


I think it's more or less like this:

http://www.geocities.com/sapta_lena/monnearth.jpg


@ Janus58: I hope you dont mind I grab your animation :p

Which sort of contradicts your comment about "turning" to keep one face toward the viewer in the centre.
It can't turn on its own axis because the string anchors it.

No, it turns because of the string. One rotation on its own axis per revolution around your head. The string just prevents it from rotating at any different rate than this one to one ratio.

I think the problem some people are having is in separating the concepts of orbital motion from the rotation of the object around it own axis.

Orbital motion is simply the path the center of gravity of the moon takes around the planet.
Rotational motion is how the moon changes the direction it faces over time.

The two motions are completely separate and independent of each other.

It seems that some seem to think that if we say one object "orbits" another, that keeping one side always facing the object it orbits is assumed to be part of its orbital motion. As if this is the natural state of an "orbit". It is not. There is no connection between an object's orbit and the direction it faces.

When we do see such a correlation, it is because outside forces (such as tidal forces, or the tug of a string) have acted on the object to cause it.

Ya, but it's turning on an axis at the end of the string (i.e. your head) not its own axis.

Ya, but it's turning on an axis at the end of the string (i.e. your head) not its own axis.

Two separate motions measured with respect to two different reference points, and it's doing both

This is an object traveling around a central axis and not turning on its own axis.

http://home.earthlink.net/~parvey/sitebuildercontent/sitebuilderpictures/orbitamin2.gif

And the one in this post:

http://sciforums.com/showpost.php?p=1504422&postcount=108

is doing both.

If you were an ant on the string tied ball, which is orbiting a second larger object, (ball always presenting only one side to larger object of course) and smart enough to note in which direction the string was pointing out into space, then you would see that "sting extended point" in the heavens moving around large circle amoung the stars. Thus the string tied ball is rotating.

MORE GENERALLY:

Any motion of any ridged body can be considered to be composed of two distinct types of motion: Rotation and Translation.

A vector (or speed & direction if you are not familiar with vectors) is associated with both and these vectors can change with time, but at any given instant, their directions are uniquely defined.

EXAMPLE:
Translation part:
If you place yourself on the rigid object and have the normal egotistical attitude then you do not consider that you are translating. For example while sitting at your desk you actually have a very complex translation with the sun thru space (in essentially a constant direction and speed, neglecting the small wobble Jupitor makes in the sun's trajectory thru space) and you are also in near circular orbit about the sun, so this is the next major part of your translation motion but now the direction of this slower component is not constant. It is constantly and steadly changing (after one year it will start repeating). There is still a third and minor component of your total translation, due to fact your desk is not at the mass center of the Earth (actually the Earth moon system as that is what is orbiting the sun, not the Earth).

Rotation part:
Even though you sit facing your desk and looking out the large window on the other side of the desk for 24 hours without thinking that you are rotating you are in fact rotating. For example, you see the sun rise and about half a day later you see it set thru the window. Now for most of man's history it was thought that you were not rotating and that the sun was going around the Earth, but I am assuming you know better than ancient man did. Thus, you are rotating even if sitting at your desk with both your hands glued to the desk. Your rotational rate is 15 degrees/ hour.

POINT of this example:
Is that you should "look to the heavens", not your local enviroment, to tell if you are rotating or not.*

(Leaving the example and returning to the ant on the ball):

Yes, it sure seems to the ant (from his local obsservations) that he is not rotating, but this is a very intelligent ant. He knows how to tell if he is rotating or not. He saw the string sweep out a 360 degree circle in the heavens while he made one orbit around the "larger object" so he understood that despite the local appearances, he was rotating.

Please be smarter than ancient man and as smart as that ant. :D

PS to Janus58:
For god's sake let them continue to think the moon is orbiting the Earth. - I am not up to showing that is an erroneous concept. (One I held until you explained the error to me. - thanks again for doing so.)
--------------------------
*Initially I had "must" instead of "should" in this sentence and only changed as it is not technically true with "must." (If you could precisely measure gravity at all points of interest and exactly determine the shape of a liquid surface, you could also tell if you were rotating, even if you could not observe the heavens. - Think what shape water takes in a bucket if it is rotating water to understand the point.)

I think it's more or less like this:

http://www.geocities.com/sapta_lena/monnearth.jpg


@ Janus58: I hope you dont mind I grab your animation :p

Hallelujia and praise be to inzomnia!! I THINK I GOT IT!! In my head, I had a different axis. So sometimes the man in the moon is upside down?

Eheheh, not really, actually I heard the angle should be somewhat tilted. :p


So sometimes the man in the moon is upside down?


I dont think so. Its like on earth, there is this gravity that help us to stay not upside
down. But I am not sure though, what if we are in the middle/core center inside
the moon, maybe it could be at some point upside down, lol.

Hallelujia and praise be to inzomnia!! I THINK I GOT IT!! In my head, I had a different axis. So sometimes the man in the moon is upside down?

Sorry, but no. The moon's axis does not point along the line joining it with the Earth. Besides with such an arrangement, the axis could only point along that lie at two points of the orbit, As the axis would always point in the same direction relative to the image no matter where it was relative to the Earth.


Here's another try at a animation to get the idea across. This one shows the Libration I talked about earlier.

In it, the planet still makes one rotation per orbit of the Moon. The Moon also makes one rotation per orbit. (note that the Planet's red and white sides always face the same way.

The orbit however is now elliptical. In this case the moon travels faster in its orbit when it is nearer the planet then when it is further away. Notice how the moon does not always keep the same point facing the Planet. (the part of the moon visible to fromt he planet is shown as brighter in the image.)

IOW, both the moon and planet rotate around their axie at a constant rate while the orbit varies in speed.

http://home.earthlink.net/~parvey/sitebuildercontent/sitebuilderpictures/librationanim.gif

P.S. the orbital speed to distance ratio does not match that of a actual satellite, and is only a rough aproximation. I just didn't want to spend the extra time fitting in the proper equations, since it did not effect the principle demonstrated.

I think you've got to specify which frame of reference you are speaking of, and rotating relative to what.

For example, an astronaut sitting on the surface of the moon and looking at Earth directly overhead would correctly conclude the moon is not rotating on its axis relative to the Earth. The Earth would stay in essentially the same location throughout the month. The astronaut would see the Earth spinning on its axis. The astronaut would see the sun move across the horizon, taking 28 days to come back to the same location in the sky. The moon is rotating relative to the sun and the stars, but it is not rotating relative to the Earth.

Next, consider that we changed the orientation of the moon's axis exactly 180 degrees. North was now south, etc. The astronaut sitting on the moon would see no difference in his observation of the Earth. An observer on Earth would see no difference in his view of the tidally locked side of the moon. But the astronaut sitting on the moon would see the sun reverse its direction across the moon's horizon. Again, the moon is rotating relative to the sun and the stars, but it is not rotating relative to the Earth. It's a matter of frame of reference as to whether the moon is rotating or not.

I think you've got to specify which frame of reference you are speaking of, and rotating relative to what.

For example, an astronaut sitting on the surface of the moon and looking at Earth directly overhead would correctly conclude the moon is not rotating on its axis relative to the Earth. The Earth would stay in essentially the same location throughout the month. The astronaut would see the Earth spinning on its axis. The astronaut would see the sun move across the horizon, taking 28 days to come back to the same location in the sky. The moon is rotating relative to the sun and the stars, but it is not rotating relative to the Earth.

Next, consider that we changed the orientation of the moon's axis exactly 180 degrees. North was now south, etc. The astronaut sitting on the moon would see no difference in his observation of the Earth. An observer on Earth would see no difference in his view of the tidally locked side of the moon. But the astronaut sitting on the moon would see the sun reverse its direction across the moon's horizon. Again, the moon is rotating relative to the sun and the stars, but it is not rotating relative to the Earth. It's a matter of frame of reference as to whether the moon is rotating or not.

This type of change of refernce doesn't address the situation at hand. While the Astronaut might not consider himself rotating relative to the Earth, neither does he consider himself revolving around it.

The question at hand is:

From a reference frame in which the moon is considered as revolving around the Earth, is it also rotating around its own axis? and the answer is yes.

Janus58,
This type of change of refernce doesn't address the situation at hand. While the Astronaut might not consider himself rotating relative to the Earth, neither does he consider himself revolving around it.
That is actually a strawman argument, Janus58. The astronaut sitting on the moon is not rotating relative to the Earth. He is revolving around the Earth, which he can easily determine by looking at the stars' motion. An anology would be our familiar merry-go-round oft used in science. A person sitting on the edge of revolving merry-go-round would represent the astronaut on the moon. Both are revolving around a central axis. Do we normally state the person on the merry-go-round is rotating on his axis (or ass, :D )? In the frame of reference of a bystander not on the merry-go-round (consider one on the sun for the moon), the bystander will see all sides of the revolving rider, just as an observer at the sun would see all sides of the moon. The reason those observers see all sides of the rider and the moon is due only to their revolving around a distant axis, not because they are rotating on their own axis. I know you are explaining it as is written in textbooks and online physics sites, but the part about the moon rotating on its own axis is a bit a of a semantics mistake, I believe. The moon does rotate in a global frame of reference, but it does not rotate about its own axis because it is tidally locked with the Earth.

Wrong, wrong, wrong. oh so wrong.
Really nothing more need be said.

why does the white side of the earth never see the moon?

why does the white side of the earth never see the moon?

The animations aren't meant to exactly reproduce the Earth and Moon, but a simular situation where the planet makes one rotation in the same time as the moon makes one orbit. I did this for two reasons.

1. If I reproduced the actual rotation of the Earth, it would have to rotate 27.3 times for every orbit. In essence, it wouldn't be a red and white ball but a pink blur of one.

2. The rate at which the planet rotates doesn't matter in the situation being discussed, so I picked a convenient one, one which showed how the directions which the rotating planet and the moon faced always stayed the same. It was an additional visual aid to try and get the concept across.

Janus58,

That is actually a strawman argument, Janus58. The astronaut sitting on the moon is not rotating relative to the Earth. He is revolving around the Earth, which he can easily determine by looking at the stars' motion. An anology would be our familiar merry-go-round oft used in science. A person sitting on the edge of revolving merry-go-round would represent the astronaut on the moon. Both are revolving around a central axis. Do we normally state the person on the merry-go-round is rotating on his axis (or ass, :D )? In the frame of reference of a bystander not on the merry-go-round (consider one on the sun for the moon), the bystander will see all sides of the revolving rider, just as an observer at the sun would see all sides of the moon. The reason those observers see all sides of the rider and the moon is due only to their revolving around a distant axis, not because they are rotating on their own axis. I know you are explaining it as is written in textbooks and online physics sites, but the part about the moon rotating on its own axis is a bit a of a semantics mistake, I believe. The moon does rotate in a global frame of reference, but it does not rotate about its own axis because it is tidally locked with the Earth.

Hmm. how to put this, oh yeah,

http://www.youtube.com/watch?v=WrjwaqZfjIY

I know it's a but flippant, But any time someone says that they are right and the textbooks wrong, I think its deserving.

Janus58,
I know it is a bit flippant, but appeal to the youtube is not an argument. Point out my mistake, if you can, and explain the definition of 'tidally locked' while you are at it. An example of rotation would be the gondola of a farris wheel. The gondola rotates about its axis within the frame of the farris wheel as the farris wheel revolves around its own axis. Or do you claim the gondola does not rotate on its axis? I also recall you stating that the moon did not orbit the Earth, but it was an illusion caused by the moon's and the Earth's mutual orbit of the sun. Textbooks state that the moon orbits the Earth well within the Earth's Hill sphere, thus it orbits the Earth. Were you stating the textbooks are wrong, or were you wrong when you made the argument?

Janus58,

That is actually a strawman argument, Janus58. The astronaut sitting on the moon is not rotating relative to the Earth. He is revolving around the Earth, which he can easily determine by looking at the stars' motion. An anology would be our familiar merry-go-round oft used in science. A person sitting on the edge of revolving merry-go-round would represent the astronaut on the moon. Both are revolving around a central axis. Do we normally state the person on the merry-go-round is rotating on his axis (or ass, :D )? In the frame of reference of a bystander not on the merry-go-round (consider one on the sun for the moon), the bystander will see all sides of the revolving rider, just as an observer at the sun would see all sides of the moon. The reason those observers see all sides of the rider and the moon is due only to their revolving around a distant axis, not because they are rotating on their own axis. I know you are explaining it as is written in textbooks and online physics sites, but the part about the moon rotating on its own axis is a bit a of a semantics mistake, I believe. The moon does rotate in a global frame of reference, but it does not rotate about its own axis because it is tidally locked with the Earth.

Egad - where in the world did THIS come from???

You took something very, very simple and turned it into a complex, convoluted mess absolutely full of errors!

I'd suggest you study a bit more on this topic. In fact, you can get what you need to know simply by re-reading all the valid posts in this thread.

How wonderful he didst create this masterpiece.

Look upon its size...it doth fit the Sun like a well placed coin during an eclipse.

Its cycle doth coincide exactly to a female period.

It doth show its only side in perfect confluence with thee exact synchronocity ov rotation.

It doth then result in thy biggest selling albumof all time...Thee Dark Side of thee Moon.

Moon...we worship thy female goddess nature.


All that you touch
All that you see
All that you taste
All you feel.
All that you love
All that you hate
All you distrust
All you save.
All that you give
All that you deal
All that you buy,
beg, borrow or steal.
All you create
All you destroy
All that you do
All that you say.
All that you eat
And everyone you meet
All that you slight
And everyone you fight.
All that is now
All that is gone
All that's to come
and everything under the sun is in tune
but the sun is eclipsed by the moon.

"There is no dark side of the moon really. Matter of fact it's all dark."

Janus58,
I know it is a bit flippant, but appeal to the youtube is not an argument.
It was not meant to be an argument, just a statement.
Point out my mistake, if you can,
OK

The astronaut sitting on the moon is not rotating relative to the Earth. He is revolving around the Earth, which he can easily determine by looking at the stars' motion.
Let's start here. The astronaut cannot determine that he is revolving around the Earth by looking at the stars (excluding using parallax.). He can conclude that the moon is rotating on its axis or that that the stars are revolving around him. (in which case, the Earth is simply suspended overhead). The reason being that the moon's orbital path around the Earth has nothing to do with a moon-based observer's perception of the stars motion. A case in point, as I already have pointed out, the Moon has an eccentric orbit. and travels around the Earth at different speeds during its orbit. An observer on the moon would not see the motion of the stars vary to match however.
He could conclude that he was revolving around the Earth, In which case, he would have to automatically conclude that the moon was also rotating in order to keep the Earth in the same place in the Moon's sky. (actually oscillating around a point in the sky due to the varience of orbit.)

An anology would be our familiar merry-go-round oft used in science. A person sitting on the edge of revolving merry-go-round would represent the astronaut on the moon. Both are revolving around a central axis. Do we normally state the person on the merry-go-round is rotating on his axis (or ass, )? In the frame of reference of a bystander not on the merry-go-round (consider one on the sun for the moon), the bystander will see all sides of the revolving rider, just as an observer at the sun would see all sides of the moon. The reason those observers see all sides of the rider and the moon is due only to their revolving around a distant axis, not because they are rotating on their own axis.
No, you see what you see because the rider both revolves around the center and rotates on it own axis. Revolving around an axis does not automatically imply that the object changes the direction it faces as it does so. If the carousel horse and rider were not rigidly tied to the carousel, but rather attached by a pole passing through their Cog though frictionless bearings, then the observer would not see different sides of the rider and he revolved around the center, bt rather the same side at all times.

I know you are explaining it as is written in textbooks and online physics sites, but the part about the moon rotating on its own axis is a bit a of a semantics mistake, I believe. The moon does rotate in a global frame of reference, but it does not rotate about its own axis because it is tidally locked with the Earth.

and explain the definition of 'tidally locked' while you are at it.

Tidal locking refers to a situatition where there is a correspondence between the period of an object's rotation and the period of it orbit due to gravitational interaction between the two bodies (in the case of the Moon. 1:1). It does not necessarily mean that it keeps the same face facing the object it orbits. Cases in point are the moon which exhibits libration and Mercury which has a 3:2 tidal lock with the Sun, where it rotates 3 times for every 2 orbits.


An example of rotation would be the gondola of a farris wheel. The gondola rotates about its axis within the frame of the farris wheel as the farris wheel revolves around its own axis. Or do you claim the gondola does not rotate on its axis?
You can't have it both ways. Either the gondola rotates around its axis within the frame of the ferris wheel and within said frame The ferris wheel does not rotate around its axis, or Or the Ferris wheel rotates around its axis, while the gondola travels around this axis, while not rotating around its own. You are trying to eat your cake and have it too.

I also recall you stating that the moon did not orbit the Earth, but it was an illusion caused by the moon's and the Earth's mutual orbit of the sun. Textbooks state that the moon orbits the Earth well within the Earth's Hill sphere, thus it orbits the Earth. Were you stating the textbooks are wrong, or were you wrong when you made the argument?

Actually, I said that it could be argued that the Moon primarily orbits the Sun, and thus secondarily orbits the Earth and that thus the Earth-Moon system could be considered a double planet rather than planet-satellite system. The recent definition of planet however appears to preclude this designation.
The particulars of the Earth-Moon-Sun orbital characteristics can be found in any good textbook,(One I have discusses both the Moon's Geocentric and Heliiocentric orbits). and some textbooks might even have broached the subject of the Earth-Moon system definition.

OTOH, no text book would allow for simultaneously considering the Moon revolving around the Earth, and not rotating around its own axis as you have tried to do.

I'd just like to note here that inzomnia's picture is wrong.

The Moon's axis of rotation is parallel to the Earth's axis; the Moon's axis does not point radially towards the Earth as in the diagram.

If inzomnia's picture was correct, then we would not always see the surface features of the moon with the same orientation. Instead, we'd see the moon appear to rotate as we looked at it in the sky - sometime the "man in the moon" would be the right way up, sometimes upside down, sometimes sideways, from our point of view on Earth. Obviously, that is not what we see from a fixed point on the Earth's surface.

Everything in this world is tilted in relation to something.

So the moon is as well.

http://www.jb.man.ac.uk/distance/strobel/nakedeye/nakedeyc_files/moonorbb.gif

Janus58,
The astronaut cannot determine that he is revolving around the Earth by looking at the stars (excluding using parallax.). He can conclude that the moon is rotating on its axis or that that the stars are revolving around him. (in which case, the Earth is simply suspended overhead). (my italics)
If the astronaut concludes the moon is rotating on its axis, he must also conclude the Earth orbits himself and the moon in synchronicity with the rotation of the moon, or else the Earth would not stay almost motionless in his sky. An intelligent astronaut could measure the relative masses of the Earth and moon and conclude that the much larger mass of the Earth is not orbiting the smaller mass of the moon. Therefore, he concludes the moon is orbiting (revolving around) the Earth and that the moon is not rotating on its axis relative to the Earth. He could also conclude the moon does rotate relative to the 'fixed' stars. Those are the frames of reference I was speaking about that you insist on ignoring.
If the carousel horse and rider were not rigidly tied to the carousel, but rather attached by a pole passing through their Cog though frictionless bearings, then the observer would not see different sides of the rider and he revolved around the center, bt rather the same side at all times.
And if a frog had wings, he wouldn't have to bump his ass every time he took a step. :D
It does not necessarily mean that it keeps the same face facing the object it orbits. Cases in point are the moon which exhibits libration and Mercury which has a 3:2 tidal lock with the Sun, where it rotates 3 times for every 2 orbits.
Mercury is not tidally locked with the sun, that was a mistake in old textbooks. Mercury rotates three times for every two orbits around the sun. It is called a 3:2 spin-orbit resonance, not a tidal lock.
You can't have it both ways. Either the gondola rotates around its axis within the frame of the ferris wheel and within said frame The ferris wheel does not rotate around its axis, or Or the Ferris wheel rotates around its axis, while the gondola travels around this axis, while not rotating around its own. You are trying to eat your cake and have it too.
I'm sorry, I wasn't clear as to what I meant by 'within the frame of the farris wheel'. I didn't mean the farris wheels frame of reference, but the actual circular steel frame that the gondula is attached to. The gondula rotates within the circular steel frame as the steel frame rotates relative to a ground observer.
Actually, I said that it could be argued that the Moon primarily orbits the Sun, and thus secondarily orbits the Earth and that thus the Earth-Moon system could be considered a double planet rather than planet-satellite system. The recent definition of planet however appears to preclude this designation.
I wasn't necessarily objecting to your description, but rather to your model differing from that written in most elementary textbooks. I always understood that the primary disagreement with your model was because the barycenter of rotation ( the center of mass) of the Earth/moon system fell within the physical body of the Earth.

I'd just like to note here that inzomnia's picture is wrong.

The Moon's axis of rotation is parallel to the Earth's axis; the Moon's axis does not point radially towards the Earth as in the diagram.

If inzomnia's picture was correct, then we would not always see the surface features of the moon with the same orientation. Instead, we'd see the moon appear to rotate as we looked at it in the sky - sometime the "man in the moon" would be the right way up, sometimes upside down, sometimes sideways, from our point of view on Earth. Obviously, that is not what we see from a fixed point on the Earth's surface.

Not only that, but in reality, it wouldn't be possible for the Moon to keep its axis of rotation pointing at the Earth through out the entire orbit. In which case, with one rotation per orbit, we would see something like this over the course of an orbit:

http://home.earthlink.net/~parvey/sitebuildercontent/sitebuilderpictures/weirdrot.gif

Janus58,
(my italics)
If the astronaut concludes the moon is rotating on its axis, he must also conclude the Earth orbits himself and the moon in synchronicity with the rotation of the moon, or else the Earth would not stay almost motionless in his sky. An intelligent astronaut could measure the relative masses of the Earth and moon and conclude that the much larger mass of the Earth is not orbiting the smaller mass of the moon. Therefore, he concludes the moon is orbiting (revolving around) the Earth and that the moon is not rotating on its axis relative to the Earth. He could also conclude the moon does rotate relative to the 'fixed' stars. Those are the frames of reference I was speaking about that you insist on ignoring.

You are confusing "point of view" and "frame of refernce", they are not the same thing. Once the Astronaut concludes that the Moon is revolving around the Earth, he uses that frame of reference to determine that the moon is rotating to maintain the same face to the Earth, regardless of what "his point of view" says. He doesn't use one frame of reference to measure the revolution and another for the Moon's rotation. That would be no different than saying that while the Earth travel's around the Sun, we measure the Earth's rotaion around its own axis relative to itself, and the Earth doesn't rotate. You don't measure the moon's revolution around the Earth by a different reference than you do its rotation.

And if a frog had wings, he wouldn't have to bump his ass every time he took a step. :D
If you are quite through being foolish.
The situation of the Horse and rider set on frictionless bearings is a much closer analogy to a moon orbiting a planet than one where they are rigidly attached to the frame of the carousel.
If it is the term "frictionless" that you are worried about, it is perfectly allowable condition in a theorectical example. But if you insist, we can replace it with "extremely low friction"( Just enough frction so that after some few hundred million or so trips around the carousel, the horses will match the rotation of the carousel.). That would make it even a closer analogy to an orbiting moon. Add in that the carousel changes it speed over the course of a rotation, and you come even closer to the Earth-Moon system.
The point of the argument remains the same; there is no special conection between the direction the horses face and their circular motion around the center of the carousel.
Mercury is not tidally locked with the sun, that was a mistake in old textbooks.
Don't put words into my mouth, I never said or implied that Mercury kept one side towards to the Sun. I explictly said that it had a 3:2 rotation to revolution ratio
Mercury rotates three times for every two orbits around the sun. It is called a 3:2 spin-orbit resonance, not a tidal lock.

And the Moon has a 1:1 resonance. Actually, it is a moot point whether or not the term "tidal lock" is limited to just 1:1 resonances or includes others.

On another note, I'm surprised that you aren't claiming that Mercury is in a 1:2 resonance (rotates once for every 2 orbits). After all, its Solar day is 176 days compared to its 88 day orbit. Since you seem to think that the Moon's rotation should be judged by the Earth's preceived motion in its sky, then it seems that, to be consistant,you should claim that Mercury's would be judged by the Motion of the Sun in its sky.


I'm sorry, I wasn't clear as to what I meant by 'within the frame of the farris wheel'. I didn't mean the farris wheels frame of reference, but the actual circular steel frame that the gondula is attached to. The gondula rotates within the circular steel frame as the steel frame rotates relative to a ground observer.
Again, you seem to want to jump back and forth between points of view and frames of reference willy nilly whenever you wish.

Let's approach this from another angle (so to speak).

Assume we have the situation as mentioned earlier in this thread where the moon's axis lies parallel to the plane of it orbit(90° axial tilt), and it rotated on its axis once per orbit (relative to the stars), and appears from the Earth as I show in my last post. You'd agree that the Moon does indeed rotate on its axis in this case wouldn't you, and if not, why not?

Now make the axial tilt 80°, is it still rotating on its axis? At 70°, 45° or 30°?

And at what point between 90° and 0° axial tilt do you claim that the moon suddenly stops rotating on its axis?

As an old teacher, I seldom give up on a "Hopeless Student."

Now imagine that the "moon" in the animation is slowing enlarging until it is equal to the "Earth" and both orbit their common mass center. Which one is not rotating? The moon? Ok, then change the labels on these identical co-orbiting objects so now, with the new labels applied, would you claim the Earth is not rotating?

Duh! I was the first one to explain tidal force induced synchronous orbit in this thread.

Well i would