1. Originally Posted by Dave Lee
Thanks
I do understand your point of view.
Actually, I fully accept the idea that the Moon orbits around the Earth, although, it can get twice stronger gravity force from the Sun.
It seems to me that even if the gravity force of the Sun will be 4 times stronger than the Earth, the Moon will still continues to orbit around the Earth.
Based on my knowledge as Electronic Engineer, I will call it "Threshold".
Which means, that the moon stay at that state because it was already position at that state (bonded by Earth gravity).
However, based on the "Threshold" analogy, the moon won't set that gravity connection at the first stage without getting higher gravity force by the Earth.
Do you agree with that analogy?
No, it doesn't apply. The moon doesn't choose one body or another to orbit, according to which provides the largest gravitational acceleration. It responds to the gravity of both, all the time. And it orbits both, all the time.

Grant Hutchison

2. Originally Posted by Dave Lee
Thanks
I do understand your point of view.
Actually, I fully accept the idea that the Moon orbits around the Earth, although, it can get twice stronger gravity force from the Sun.
It seems to me that even if the gravity force of the Sun will be 4 times stronger than the Earth, the Moon will still continues to orbit around the Earth.
Based on my knowledge as Electronic Engineer, I will call it "Threshold".
Which means, that the moon stay at that state because it was already position at that state (bonded by Earth gravity).
However, based on the "Threshold" analogy, the moon won't set that gravity connection at the first stage without getting higher gravity force by the Earth.
Do you agree with that analogy?
If so, we have to ask: Why the Earth could offer higher gravity force at the first moment?
It has nothing at all to do with thresholds. There are no discontinuities. There is no sort of hysteresis. There is no "connection". Gravity does not have any sort of "state".

The motion of the moon is due to the combined gravitation of the Earth, the sun, Jupiter, Venus, all the other planets, and every rock, speck of dust, and stray gas atom in the solar system, as well as that of all the stars, planets, and other assorted objects of the Milky Way, and those of every other galaxy in the universe.

As you've been told many times before, the two-body problem is an idealization, a simplification of real-world systems. There isn't an object anywhere in existence that follows a perfect orbit around a single primary.

3. Originally Posted by Dave Lee
Thanks
I do understand your point of view.
Actually, I fully accept the idea that the Moon orbits around the Earth, although, it can get twice stronger gravity force from the Sun.
It seems to me that even if the gravity force of the Sun will be 4 times stronger than the Earth, the Moon will still continues to orbit around the Earth.
Based on my knowledge as Electronic Engineer, I will call it "Threshold".
Which means, that the moon stay at that state because it was already position at that state (bonded by Earth gravity).
However, based on the "Threshold" analogy, the moon won't set that gravity connection at the first stage without getting higher gravity force by the Earth.
Do you agree with that analogy?
If so, we have to ask: Why the Earth could offer higher gravity force at the first moment?
Since you did not give any specifics about an electronics situation involving thresholds, I cannot agree or disagree about an analogy.

It appears that you are concerned about how the Earth could have captured a previously unbound Moon without having stronger gravity than it does now. That would have required a close encounter with another massive object at or near the time of the Moon's close approach. If the encounter geometry is just right, the other object's gravity could slow the Moon relative to the Earth just enough to make a capture happen, with the interloper being flung away by the kinetic energy exchange. This would be roughly analogous to using a retro rocket to slow a spacecraft down enough to become bound to a planet when it otherwise would have been a flyby, never to return. Such an encounter is considered highly improbable, and now the preferred theory is a collision with a Mars-sized body. Such a collision would break a lot of material loose from both bodies. Most of it would fly away, but if the geometry is favorable a relatively small portion could be moving slowly enough to remain gravitationally bound the the proto-Earth and become the Moon.

As for how much stronger the Sun's gravity could be and still not disrupt the Moon's orbit, the sky is the limit in principle. In a thought exercise we could substitute a billion solar mass black hole for the Sun and place it 1,000 astronomical units away. That would make the overall strength of the central body's gravity 1,000 times what we actually have, but the difference in strength at the Earth and Moon positions would be no greater than what we actually have, because of the inverse cube law for that effect. Thus the Earth's gravitational effect on the Moon would still be 100 times stronger than the disruptive effect of the black hole.

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Regarding my image of a portion of the Earth and Moon's orbit
around the Sun:
Originally Posted by Strange
So its meant to be only a tiny bit of the orbit? (I assumed I was
My apologies to you and Dave and anyone else who may have
been annoyed by that. I'll try to get around to upgrading it....

Originally Posted by Strange
It would be interesting to see the whole orbit in one image - then
you could zoom out to see the whole thing or zoom in to see the
little slice you have posted.
The computer I used to make it (back in 2009, for a thread here
on BAUT/CosmoQuest) only has an 800 x 600 pixel screen.
At the scale I chose to use, 1 pixel = 100,000 kilometres, the circle
representing the Earth-Moon barycenter is about 3000 pixels in
diameter. I had to make an entire circle in my graphics creation
program. It doesn't have an option to make an arc. So the full
image was something over 3000 x 3000 pixels. When reduced
enough to fit on the 800 x 600 screen, the circle was very spotty.
Dots and dashes instead of a solid line. I chose to keep only a
width that I thought most readers would be able to view full-size
on their monitors, 1600 pixels. A height of 260 pixels was enough
to show the orbits going to the left and right edges of the image,
so adding more height wouldn't be useful. A modern 4K screen
has 4096 x 2160 pixels, so it could show the full width of the
orbit, and the image could scroll up and down.

The monochrome CRT monitor I saw demonstrated in the 1980's
was 5000 x 5000 pixels.

-- Jeff, in Minneapolis
Last edited by Jeff Root; 2018-Jan-29 at 12:07 AM.

5. Originally Posted by Dave Lee
In one hand you claim that "dust and gas that was orbiting the sun", so it seems that this matter is under the Sun gravity, however, in the next hand you claim: "It formed because a denser-than-average volume".
So, what is the source of that power which had set that denser-than-average volume? if it isn't the Sun Gravity while it is orbiting the Sun, than what is it?
You really seem to be having difficulty understanding that even while both the earth and the moon orbit the sun, they are simultaneously attracted to one another. And the International Space Station is orbiting the sun while simultaneously orbiting the earth (and being attracted to the moon as well). Everything in the universe is attracted to everything else in the universe. Until you can understand that and visualize it somehow I think you are going to have difficulty understanding how things work.

6. Originally Posted by Jens
You really seem to be having difficulty understanding that even while both the earth and the moon orbit the sun, they are simultaneously attracted to one another.
Ideally, post 20 should make it plainly apparent to Dave that one gravity well can live embedded in a larger gravity well.

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Originally Posted by Dave Lee
So, what is the source of that power which had set that denser-than-average volume?
No "power" involved. A molecular cloud has mostly gas molecules and some dust particles moving randomly. Chance alone will create volumes that are denser then average. In addition, shock waves from supernova can also cause over-dense regions as speculated for the formation of the Solar System.
See Nebular hypothesis and Formation and evolution of the Solar System.

Originally Posted by Dave Lee
Few more question:...
There is no assumption that "the Earth and Moon had been formed separately". The origin of the Moon is based on evidence. The most plausible explanation for the Moon is the giant-impact hypothesis.

We do not assume "they both had been formed together at the same moment", etc. (see above).

We do not "set a gape of about 2 Billion years between the Sun formation to Planets/Moons formation". Age of Sun = approximately 4.6 billion years. Age of Earth = approximately 4.54 ± 0.05 billion years.

The "same power (or process)" did create the entire Solar System - see the Wikipedia articles above.

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I believe that the number-one cause of denser regions *inside* a
giant molecular cloud is that the dust particles shield the interior
from the light of nearby stars. Some parts of the interior cool
more than other parts. The cooler parts become more dense.
Those regions can eventually collapse to protoplanetary disks.

-- Jeff, in Minneapolis

9. Originally Posted by Jeff Root
My apologies to you and Dave and anyone else who may have
been annoyed by that.
That's OK. Not annoyed just confused.

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Originally Posted by Jens
even while both the earth and the moon orbit the sun, they are simultaneously attracted to one another.
Yes, that that is correct.

Originally Posted by Jens
And the International Space Station is orbiting the sun while simultaneously orbiting the earth (and being attracted to the moon as well).
Don't you think that the Space station is orbiting around the Earth while the Earth is orbiting around the Sun?
If the Earth will be stripped away from the Sun, don't you agree that the Space station should continue to orbit around the Earth and not around the Sun?

Originally Posted by Jens
Everything in the universe is attracted to everything else in the universe.
That is correct.
However,
We must distinguish between orbital path to general "attracted" power.
So even if the moon is attracted by Pluto, or the Space station is attracted by the Moon, it has no real impact on the orbital path (maybe some sort of tidal).
Therefore, do you agree that there is some difference between orbital path to tidal?
Last edited by Dave Lee; 2018-Jan-29 at 01:53 PM.

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Originally Posted by cjameshuff
It has nothing at all to do with thresholds. There are no discontinuities. There is no sort of hysteresis. There is no "connection". Gravity does not have any sort of "state".
I'm not sure that I understand your message.
What do you mean by: "There are no discontinuities."
Do you mean that the moon will continue to orbit around the Earth at any sort of Sun gravity?
So, even if the Sun/moon gravity will be increased by 100 or over 1000 with reference to Earth/moon gravity, it won't be able to strip away the moon from the Earth?

12. How about the force due to the motion of Earth-Moon system going around the Sun it pulls the two outwards. There is balance between the forces that determines the orbit of the Earth-moon around the sun. Plus you have force from the Moon going around the Earth. The distances between everything is not static and changes from point to point. (darn this what I will be thinking about all day if not week.)
Last edited by astrotimer; 2018-Jan-29 at 02:27 PM.

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Originally Posted by Reality Check
We do not "set a gape of about 2 Billion years between the Sun formation to Planets/Moons formation". Age of Sun = approximately 4.6 billion years. Age of Earth = approximately 4.54 ± 0.05 billion years.
However, why do we set any sort of gape in time?
4.6 B - 4.54 B = 0.06 Billion.
So, even if it is quite close to the error bar (± 0.05 billion years), we still have a gape of about 0.01 B year.
I wonder what is the reason for that gape?
Why don't we say that the whole Solar system had been formed about 4.54 B ± 0.06 billion years?

14. The planets took a while to form. Plus often some planets would form and then get smashed apart and start to rebuild again, we only know how old the plants that still exist have been around.

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Originally Posted by Hornblower
It appears that you are concerned about how the Earth could have captured a previously unbound Moon without having stronger gravity than it does now.
Yes, that is correct

Originally Posted by Hornblower
That would have required a close encounter with another massive object at or near the time of the Moon's close approach. If the encounter geometry is just right, the other object's gravity could slow the Moon relative to the Earth just enough to make a capture happen, with the interloper being flung away by the kinetic energy exchange. This would be roughly analogous to using a retro rocket to slow a spacecraft down enough to become bound to a planet when it otherwise would have been a flyby, never to return. Such an encounter is considered highly improbable, and now the preferred theory is a collision with a Mars-sized body. Such a collision would break a lot of material loose from both bodies. Most of it would fly away, but if the geometry is favorable a relatively small portion could be moving slowly enough to remain gravitationally bound the the proto-Earth and become the Moon.
So, in order to place the moon in place, there is a requirement for "another massive object at or near the time of the Moon's close approach."
How do we get this massive object at the requested size, requested position and requested timing.
Don't you think that the chance for that is very low?

Look how many moons there are in our system.
Think how many "massive objects" are requested to place all the moons on track.

If there were massive objects, where are they?
Why they are not part of our current solar system?

I still can't understand why we don't assume that the Earth & moon had been formed at the same moment and at the same place?
Why do we insist on another massive object to set the gravity bond between the two?

Why can't we just assume that at the first moment the gravity power between the Moon/Earth was much higher than the Sun/Moon Gravity?
However, do you agree that in this case, that massive object isn't needed?

Originally Posted by Hornblower

As for how much stronger the Sun's gravity could be and still not disrupt the Moon's orbit, the sky is the limit in principle.
Wow.
So you claim that even if the Sun/Moon gravity will be increased dramatically (sky is the limit) with regards to the Earth/moon Gravity - the moon won't be stripped from the earth orbital path.
Last edited by Dave Lee; 2018-Jan-29 at 09:05 PM.

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Originally Posted by astrotimer
The planets took a while to form. Plus often some planets would form and then get smashed apart and start to rebuild again, we only know how old the plants that still exist have been around.
Do you agree that we know the current status of our Solar system, but we really don't know how was it when it was formed?

17. Originally Posted by Dave Lee
Do you agree that we know the current status of our Solar system, but we really don't know how was it when it was formed?
I think we know roughly how it is created but we do not and probably never know every collision that had taken place over time.

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"The Moon is thought to have formed about 4.51 billion years ago, not long after Earth. The most widely accepted explanation is that the Moon formed from the debris left over after a giant impact between Earth and a Mars-sized body called Theia."

from the Wiki aricle Moon.

Dave, do you dusagree with this mainstream explanation? If so, what do you propose as an alternatyve?

19. Originally Posted by John Mendenhall
Dave, do you dusagree with this mainstream explanation? If so, what do you propose as an alternatyve?
No, the OP will not be advocating any alternatives in the Q&A forum.

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"The Moon is thought to have formed about 4.51 billion years ago, not long after Earth. The most widely accepted explanation is that the Moon formed from the debris left over after a giant impact between Earth and a Mars-sized body called Theia."

from the Wiki aricle Moon.

Dave, do you dusagree with this mainstream explanation? If so, what do you propose as an alternatyve?
Last edited by John Mendenhall; 2018-Jan-29 at 05:50 PM. Reason: duplication

21. Originally Posted by John Mendenhall
"The Moon is thought to have formed about 4.51 billion years ago, not long after Earth. The most widely accepted explanation is that the Moon formed from the debris left over after a giant impact between Earth and a Mars-sized body called Theia."

from the Wiki aricle Moon.

Dave, do you dusagree with this mainstream explanation? If so, what do you propose as an alternatyve?
A good book to look to is Splat by Dana Mackenzie.

22. Sorry, the Big Splat.

23. Originally Posted by Hornblower
That would have required a close encounter with another massive object at or near the time of the Moon's close approach. If the encounter geometry is just right, the other object's gravity could slow the Moon relative to the Earth just enough to make a capture happen, with the interloper being flung away by the kinetic energy exchange. This would be roughly analogous to using a retro rocket to slow a spacecraft down enough to become bound to a planet when it otherwise would have been a flyby, never to return. Such an encounter is considered highly improbable, and now the preferred theory is a collision with a Mars-sized body. Such a collision would break a lot of material loose from both bodies. Most of it would fly away, but if the geometry is favorable a relatively small portion could be moving slowly enough to remain gravitationally bound the the proto-Earth and become the Moon.
Originally Posted by Dave Lee
So, in order to place the moon in place, there is a requirement for "another massive object at or near the time of the Moon's close approach."
How do we get this massive object at the requested size, requested position and requested timing.
Don't you think that the chance for that is very low?

Look how many moons there are in our system.
Think how many "massive objects" are requested to place all the moons on track.

If there were massive objects, where are they?
Why they are not part of our current solar system?
You posted a quote from my previous post, which I have included here, but you give the impression that you did not read all of it. You might wish to reread it before doing anything else.

24. Originally Posted by Dave Lee
I still can't understand why we don't assume that the Earth & moon had been formed at the same moment and at the same place?
Why do we insist on another massive object to set the gravity bond between the two?
Who says we are insisting on any such thing? I already said such a non-impact encounter is very improbable. That's why the experts proposed a collision hypothesis. If I am not mistaken the original idea was that they formed simultaneously out of a lumpy concentration of matter in the primordial nebula, but differences in composition discovered during the Apollo mission cast doubt on that. The collision idea only requires a glancing collision of two bodies rather than a highly improbable close encounter of three of them.

25. Originally Posted by Dave Lee
Wow.
So you claim that even if the Sun/Moon gravity will be increased dramatically (sky is the limit) with regards to the Earth/moon Gravity - the moon won't be stripped from the earth orbital path.
In my hypothetical model, yes. I stand by my calculations.

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Originally Posted by Dave Lee
Originally Posted by Jens
And the International Space Station is orbiting the sun while
simultaneously orbiting the earth
Don't you think that the Space station is orbiting around the Earth
while the Earth is orbiting around the Sun?
Both statements are completely correct:

- The Space Station is orbiting the Sun.
- The Space Station is orbiting the Earth.

One statement is not more correct than the other.

Originally Posted by Dave Lee
If the Earth will be stripped away from the Sun, don't you agree
that the Space station should continue to orbit around the Earth
and not around the Sun?
It depends on how the Earth is "stripped away". If a massive body
comes through the Solar System, passing close to the Earth, its
gravity could pull both the Earth and the Space Station out of orbit
around the Sun. But if the Flying Spaghetti Monster were to come
through and snatch the Earth out of orbit, that big jerk could yank
Earth away from the Space Station, leaving the Space Station
behind, still orbiting the Sun. Earth's gravity might not be enough
to hold onto the Space Station when Earth is suddenly jerked away
by the powerful, noodly tentacles of the Big Jerk himself.

-- Jeff, in Minneapolis

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Originally Posted by Dave Lee
However, why do we set any sort of gape in time?
Because Formation and evolution of the Solar System. More explicitly because we measure a gap (4.6 B and 4.54 B years) and thus there is a gap.
The age of the Earth is measured to be approximately 4.54 ± 0.05 billion years. The error is a measured value for the Earth, not arbitrarily assigned and not for the Solar System.

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Originally Posted by Dave Lee
So, in order to place the moon in place, there is a requirement for "another massive object at or near the time of the Moon's close approach."
How do we get this massive object at the requested size, requested position and requested timing.
Don't you think that the chance for that is very low?
Hornblower's post that you quote states just that. The "capture with a body to carry off excess kinetic energy" hypothesis is doubted because it needs a highly improbable event.
The Wikipedia article has an alternative capture hypothesis that gives the early Earth a large atmosphere to aero-brake the Moon but supported only by possible capture of irregular satellites by gas giants. That probably dubious idea for the origin of the Moon removes the need for another body but struggles with the lack of evidence for such an atmosphere.

29. Originally Posted by Hornblower
In my hypothetical model, yes. I stand by my calculations.
Addendum: At the risk of being repetitious, let me emphasize that I was specifying a billion solar mass body at 1,000 AU, not a 1,000 solar mass body at the Sun's position. For the latter, the disruptive effect between Earth and Moon would be increased a thousandfold, to about 10 times Earth's gravity, and I would expect the Moon to be ejected.

30. Originally Posted by Jeff Root
Both statements are completely correct:

- The Space Station is orbiting the Sun.
- The Space Station is orbiting the Earth.

One statement is not more correct than the other.

It depends on how the Earth is "stripped away". If a massive body
comes through the Solar System, passing close to the Earth, its
gravity could pull both the Earth and the Space Station out of orbit
around the Sun. But if the Flying Spaghetti Monster were to come
through and snatch the Earth out of orbit, that big jerk could yank
Earth away from the Space Station, leaving the Space Station
behind, still orbiting the Sun. Earth's gravity might not be enough
to hold onto the Space Station when Earth is suddenly jerked away
by the powerful, noodly tentacles of the Big Jerk himself.

-- Jeff, in Minneapolis
I assume the monster's big jerk is non-gravitational in your scenario. Is that correct?

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