The Moon's Orbit

[Chukar]

This may not be the perfect spot for this question.
If, in the distant future, the moon orbits significantly closer to the earth, what will be the effect on total lunar eclipses?
It seems to me that the moon, if it's plane of rotation does not significantly change, will always pass through the earth's shadow and be completely eclipsed. It's apparent size will grow, but so too will the diameter of the earth's shadow grow as the moon's orbit nears. But the math is beyond me. pollist [AT] verizon [DOT] net

[Chris Peterson]

This may not be the perfect spot for this question.
If, in the distant future, the moon orbits significantly closer to the earth, what will be the effect on total lunar eclipses?
It seems to me that the moon, if it's plane of rotation does not significantly change, will always pass through the earth's shadow and be completely eclipsed. It's apparent size will grow, but so too will the diameter of the earth's shadow grow as the moon's orbit nears. But the math is beyond me. pollist [AT] verizon [DOT] net

In reality, the Moon is getting farther from the Earth. At any distance the Moon has been, or will be from the Earth, the diameter of the Earth's shadow isn't that different.

[KiethHoyt]

This may not be the perfect spot for this question.
If, in the distant future, the moon orbits significantly closer to the earth, what will be the effect on total lunar eclipses?
It seems to me that the moon, if it's plane of rotation does not significantly change, will always pass through the earth's shadow and be completely eclipsed. It's apparent size will grow, but so too will the diameter of the earth's shadow grow as the moon's orbit nears. But the math is beyond me. pollist [AT] verizon [DOT] net

In reality, the Moon is getting farther from the Earth. At any distance the Moon has been, or will be from the Earth, the diameter of the Earth's shadow isn't that different.

Scientists have also found that the moon will not leave our orbit as some have suggested. Instead, it will reach a point of equilibrium and stay there.

[BDanielMayfield]

Scientists have also found that the moon will not leave our orbit as some have suggested. Instead, it will reach a point of equilibrium and stay there.

That's very interesting Kieth. Do you know when and at what distance this stable orbit is expected to be achieved? Can you also point us to the proof of this statement? As they say in Wikipedia ^{[citation desired]}.

[Chris Peterson]

Scientists have also found that the moon will not leave our orbit as some have suggested. Instead, it will reach a point of equilibrium and stay there.

That's very interesting Kieth. Do you know when and at what distance this stable orbit is expected to be achieved? Can you also point us to the proof of this statement? As they say in Wikipedia ^{[citation desired]}.

No citations (do your own homework <g>), but some more information.

What Keith said is generally correct, but not quite. The Moon will not reach an equilibrium orbit for the simple reason that there's not going to be enough time before it (and the Earth) find themselves destroyed by the evolution of the Sun into a red giant. But in principle, it would reach an equilibrium point.

Here's what's happening. Energy in the system of Earth-Moon rotation and orbit is given up to tidal heating in each, and to the tidal movement of land and water on Earth. The result is that the Earth's rotation slows, and the Moon's orbital radius increases. Given enough time, the two bodies will become tidally locked to one another (the Moon is already tidally locked to the Earth, which is why we always see the same face). Once they are locked, the tidal losses go away, and the Moon stops getting farther away. You have a very stable system. But this process would take a few billion years more than we've actually got.

[alter-ego]

This may not be the perfect spot for this question.
If, in the distant future, the moon orbits significantly closer to the earth, what will be the effect on total lunar eclipses?
It seems to me that the moon, if it's plane of rotation does not significantly change, will always pass through the earth's shadow and be completely eclipsed. It's apparent size will grow, but so too will the diameter of the earth's shadow grow as the moon's orbit nears. But the math is beyond me. pollist [AT] verizon [DOT] net

In reality, the Moon is getting farther from the Earth. At any distance the Moon has been, or will be from the Earth, the diameter of the Earth's shadow isn't that different.

Scientists have also found that the moon will not leave our orbit as some have suggested. Instead, it will reach a point of equilibrium and stay there.

That's very interesting Kieth. Do you know when and at what distance this stable orbit is expected to be achieved? Can you also point us to the proof of this statement? As they say in Wikipedia ^{[citation desired]}.

As Chris pointed out, the equilibrated, fully tidal-locked Earth/Moon orbit is billions of years from now. I've read possibly 2 billion. As an academic exercise, the limiting orbital radius can be calculated from angular momentum conservation.

► Assuming no significant changes in the moon's orbital plane/eccentricity and 100% angular momentum transfer, the Moon's orbital radius will not exceed 370,000 miles (~55% further away than now).
► Assuming the Earth/Sun distance is unchanged, the angular size ratio of the Moon to the Earth's umbral shadow ~80%, or relatively 20% smaller than it is now. This accounts for the convergence of the umbral shadow cone and that the distances are larger.

[KiethHoyt]

Another viewpoint would be that the Earth would eventually fall into a fixed-faced orbit with the moon, as the moon has already been forced into a fixed-face orbit to the Earth. Of course, as Chris and alter-ego stated, this would/could take billions of years.

Source: http://www.spaceanswers.com/solar-syste ... ths-orbit/

[Chris Peterson]

Another viewpoint would be that the Earth would eventually fall into a fixed-faced orbit with the moon, as the moon has already been forced into a fixed-face orbit to the Earth. Of course, as Chris and alter-ego stated, this would/could take billions of years.

That isn't another viewpoint. That's what is going to happen... assuming the expanding Sun doesn't destroy the Earth and Moon first, which seems likely. It's a pretty simple analysis that leaves little room for doubt.

[Ron-Astro Pharmacist]

One thing I have a hard time comprehending is how much humans may accomplish or manage to affect our environment in a thousand years let alone a million or a billion. Have you ever heard of a anyone trying to estimate capabilities of a "stable" million year old human civilization?

i.e. An educated "science fiction" scenario of us changing the earth-moon orbit for some yet-to-be-described benefit. (Oh - say using increased tides to generate power or keeping our planet's interior molten)

I've never read of any group realistically trying to imagine what might be physically possible given the time. (except for some very talented fiction writers)

[geckzilla]

Earth's tides are dominated by solar gravity... but even without that, it doesn't make much sense to spend the very large amount of energy required to move the Moon if your goal is to use tidal forces to generate energy. It's like burning down a forest to power a machine which will plant a new forest.

[Chris Peterson]

Earth's tides are dominated by solar gravity... but even without that, it doesn't make much sense to spend the very large amount of energy required to move the Moon if your goal is to use tidal forces to generate energy. It's like burning down a forest to power a machine which will plant a new forest.

Earth's tides are dominated by the Moon, not the Sun.

[geckzilla]

Well, shoot.

[Ron-Astro Pharmacist]

For me it's hard to conceive of future needs; especially way in the future. Like tomorrow.

I was just imagining we may want to adjust our orbit or the moon's orbit at some point in our future history but did not know, other than reading Sci-Fi , how to adopt a reasonable sense of technology that far removed when so much change has occurred just in my lifetime .

And I will shoot-the-moon and plan on wearing the blue shirt Friday.

[alter-ego]

Earth's tides are dominated by solar gravity... but even without that, it doesn't make much sense to spend the very large amount of energy required to move the Moon if your goal is to use tidal forces to generate energy. It's like burning down a forest to power a machine which will plant a new forest.

Earth's tides are dominated by the Moon, not the Sun.

That's for sure. The Sun's contribution is about 2 times smaller than the Moon's, and about 1/3 times the total of both.

(I just couldn't resist )

[geckzilla]

Yeah, just so you know I was still chiding myself over that hours later.

[alter-ego]

Yeah, just so you know I was still chiding myself over that hours later.

Oh, just to be clear, my targeted jest was not directed toward you at all. It plays more on an APOD discussion a couple days later.

[geckzilla]

It's alright, it scabbed over once and it can scab over again... if I can avoid picking at it...