Earth & Moon Correlation Question

[dmill1220]

HI Folks!
I have a question concerning the Moons effects on our Planet, both its Weather impact and Axial stability.
from what I've learned, the Moon is receding from us at the current rate of 1-1/2 inches per year.
Since the Moon is believed to be helping to maintain our axial tilt of 23 degrees, and also helps maintain our weather, tides, and rotational speed, and we can deduce the mass of the Moon and of the Earth, how far does it have to move away from us before it noticeably effects our rotatonal tilt and speed, and Weather?
Also, wouldnt its recession speed increase with time, and loss of gravity from each other?
Has anyone tried to make these calculations?
Dennis

[stuart]

It's all quite complicated. A paper that supplies a good review of the history of the moon's orbit is by B.G. Bills and R.D. Ray called "Lunar Orbital Evolution: A Synthesis of Recent Results" in GRL in 1999.

The moon retreats at a rate proportional to its semi-major axis to the -11/2 power (so as it gets farther away, it retreats more slowly). You can think of it this way: As they get farther apart, the tidal effects that are causing the recession will be less (since gravity is an inverse-square law), and so the retreat rate will lessen because there's less of a pull.

But, this also depends upon the Love number and quality dissipation factor, where hte Love number is effectively how much extra pull Earth has on the Moon due to tidal deformation, and the quality dissipation factor is how easily Earth re-forms back to a "sphere" once it was tidally pulled. This changes with time due to the changing intensity of the tides due to continental drift.

It has been modeled for the past few billion years (sample is in that paper), and the Love number and dissipation quality have changed A LOT through time. Hence, it would be really really hard to predict how it will change in the future.

However, needless to say, it will be a long time before anything significant happens. And remember that as the moon retreats, conservation of angular momentum means that Earth's rotation rate (the day) will slow down, too, so eventually the two will become tidally locked. It is unknown what will happen then, if it will stay that way, continue to retreat, or spin back to Earth.

[Blue Fire]

Dennis:

I don't know at what point the Earth's tilt and/or weather will be affected noticeably. I'd guess it would be a matter of perspective though and would depend on the magnitude of any changes, or progression, over time and what you'd consider to be noticeable. I would think that tilt and weather have already been affected significantly over the past few billion years - seems like there should be evidence in the geologic/paleontological record. But in my cursory search of the net, I've been unable to find any resources mentioning tilt or weather - it's probably there though, I just haven't seen it yet.

As to the Moon's retreat from Earth, I think Stuart summed it up pretty well in saying that it's slowing down. So, the 1.5 inches a year would slowly decrease to something less than 1.5 inches/yr. The end of this article also states that Earth's rotation is slowing at the rate of 5 milliseconds per year per year:

Tidal forces between Earth and the Moon cause the Moon to recede from Earth over time. Tidal forces are stronger when the bodies are closer, so the recession was fast early in the Moon’s history. By the first few hundred million years, the Moon had moved out to an orbit more than half its present distance from Earth. The recession has not stopped; the Moon is still retreating at about 3.8 centimeters (1.5 inches) per year.

The Moon would have originated with a spin rate that differed from its orbital rate, but tidal forces have acted to slow its rotation over time. Now, the Moon rotates at the same rate that it orbits Earth, a condition called synchronous rotation. At the same time, the same forces have slowed Earth’s rotation rate. Fossil records of the daily and yearly growth patterns of corals prove that there were approximately 400 days in a year, a few hundred million years ago, meaning that Earth’s rotation has slowed at a rate of about 5 milliseconds per year, per year. Earth would have had a 14-hour day at the birth of the Earth-Moon system. If nothing happens to disturb the Earth-Moon system for the next several billion years, Earth, too, will eventually be in synchronous rotation with the Moon. At that point in time, an Earth day and month will be equal, at about 47 current Earth-days, and the Moon’s distance from Earth will be 135% of its current value.

In any case, I found this article explaining the principles involved in the retreating Moon to be quite enlightening in an easy to understand format with simple formulas and nice illustrations/diagrams! It's where I started when I was looking into the content of your orginal post about this subject.

Great post, Dennis - fascinating subject! As usual, my brain is beginning to hurt again - but in a good way. I don't have the Science Channel here yet, but I'm still hoping!!

[Dragon Star]

Originally Posted by Blue Fire

Dennis:

I don't know at what point the Earth's tilt and/or weather will be affected noticeably.

Was this a question, or a statement?

The affects of weather would be almost immediate, changes in tide affect the currents and would throw the weather pattern into chaos...where as Earth's tilt would change slowly over time, perhaps doing a fairly sudden flip on rare occurrences due to equatorial bulge from the Sun and correlations from other planets gravitational affects.

[Nokton]

Originally Posted by dmill1220

HI Folks!
I have a question concerning the Moons effects on our Planet, both its Weather impact and Axial stability.
from what I've learned, the Moon is receding from us at the current rate of 1-1/2 inches per year.
Since the Moon is believed to be helping to maintain our axial tilt of 23 degrees, and also helps maintain our weather, tides, and rotational speed, and we can deduce the mass of the Moon and of the Earth, how far does it have to move away from us before it noticeably effects our rotatonal tilt and speed, and Weather?
Also, wouldnt its recession speed increase with time, and loss of gravity from each other?
Has anyone tried to make these calculations?
Dennis

Hi Dennis, interesting point, but correct me if I am wrong.
Is not Earths rotation slowing over time? Seem to remember Earth
had a 23 hour day a long time ago, and assume the moon a bit closer then. As earth loses rotational speed, so the moon receeds, but its effects on the Earth are still the same, in balance with the dynamics
of equilibrium
Peter

[Blue Fire]

Originally Posted by Dragon Star

Was this a question, or a statement?

It was a statement.

The affects of weather would be almost immediate, changes in tide affect the currents and would throw the weather pattern into chaos...where as Earth's tilt would change slowly over time, perhaps doing a fairly sudden flip on rare occurrences due to equatorial bulge from the Sun and correlations from other planets gravitational affects.

Well, I think we are assuming that the Moon continues to retreat from Earth normally as it has been for several billion years. So, for example, if the Moon continues to retreat another 1.5 inches by next year and the Earth slows down over the next year by another 5 millisceonds, the question would be "At which point along this progression would we notice changes in tilt and weather due to the Moon's recession?" Granted that tilt could be measured each year with some precision, can we be sure what part of that tilt change (if any) is attributable to the recession of the Moon alone? Obviously, the Earth's axis does precess (by about 1 degree every 71.6 years) and is slowly moving away from pointing towards Polaris. And within that precession motion, there are "wobbles" like nutation and polar motion. But these motions will not stay exactly constant as the Moon retreats, so how do you figure/consider what a "noticeable" effect will amount to be that is due Soley to the Moon's retreat? Things will change, that is sure, but I don't think we are assuming anything like the Moon suddenly "jumping" away from us. Changes in weather may be cumulative over long periods of time, but just how the Moon's retreat (and not just its "normal" daily/monthly tidal effects on Earth) will play into those changes to result in "noticeable" weather changes is a question I can't answer.

[dmill1220]

I'm More Concerned with the Weather Changes, due to the Altering of the tides and the Atlantic Pump Effect of the Gulf stream, someone must have thought about this effect on our weather and maybe worked out the Physics as to at what point we would at least notice the effects.
I am just curious, especially since I believe that the weather Phenomenon would be the quickest to really mess us up, after all didn't it take only a small amount of temperature and climatic change in the Earth's past to cause a mass Migration of several Species as shown in the Paleontological Record of Man and Animal?
Dennis

[stuart]

Originally Posted by dmill1220

I'm More Concerned with the Weather Changes, due to the Altering of the tides and the Atlantic Pump Effect of the Gulf stream, someone must have thought about this effect on our weather and maybe worked out the Physics as to at what point we would at least notice the effects.
I am just curious, especially since I believe that the weather Phenomenon would be the quickest to really mess us up, after all didn't it take only a small amount of temperature and climatic change in the Earth's past to cause a mass Migration of several Species as shown in the Paleontological Record of Man and Animal?
Dennis

I honestly don't know about this, but here's what I'm thinking: It would take a lot. Even if we go 100 years and the moon's 4 meters farther away, that's a change in its orbit of 0.001%, which would alter its orbital period by 0.0016%, or an increase in its orbital time by about 35 seconds. That's not a lot. I think that weather changes, climate patterns, ocean currents, etc. will be much more affected on those timescales by plate movements and human intervention than by the moon's recession.

[dmill1220]

Blue Fire
I also found this in your most excellent link quote:
This paleontological evidence comes in the form of tidal rhythmites, also known as tidally laminated sediments. Rhythmites have been subjected to intense scrutiny over the last decade or so, and have returned strong results. Williams (1990) reports that 650 million years ago, the lunar rate of retreat was 1.95±0.29 cm/year, and that over the period from 2.5 billion to 650 million years ago, the mean recession rate was 1.27 cm/year. Williams reanalyzed the same data set later (Williams, 1997), showing a mean recession rate of 2.16 cm/year in the period between now and 650 million years ago. That these kinds of data are reliable is demonstrated by Archer (1996). There is also a very good review of the earlier paleontological evidence by Lambeck (1980, chapter 11, paleorotation)
As you can see, the paleontological evidence indicates that moon today is retreating from Earth anomalously rapidly. This is exactly as expected from the theoretical models that I have already referenced. The combination of consistent results from both theoretical models and paleontological evidence presents a pretty strong picture of the tidal evolution of the Earth-moon system. end quote:
It leaves me wondering again, seems that the variable may be uncalculable?
Dennis

[dmill1220]

Excellent Point Stuart! And well noted.
But if you could add the Geological and Man made problems to our weather, plus the Moon's effects on the Atlantic Pump (tidal Changes) cumulative , which already seems to be changing our weather, I would suspect that it may Hasten things up a bit, I'm not worried about the time involved Just a theoretical distance change of the Moon, which could cut off the Atlantic Pump ?
Dennis