Drifting moon. Why still so near?

[Tim the plumber]

I know there will be a good answer but since I don't know it does anyone here?

 

On a Christian website the orbital distance of the moon has been compaired to it's rate of drift away from the earth. They have come up with the result that it must have been at mimum distance some 1.5 billion years ago. How are they wrong?

 

Here's the link;

 

http://creation.com/the-moon-the-light-that-rules-the-night

[D H]

Start with a bad assumption, and you'll get a bad answer. Add in an overly simplistic model and you'll get an even worse answer.

 

Young assumed that the current lunar recession rate is the lowest it's ever been. That's just wrong. There is a lot of history embedded in rock that tells how the length of a day has changed over the course of time. This in turn yields clues toward the rate at which the Moon has been receding from the Earth over time. The current rate is anomalistically high, about twice the average value for the past two billion years. Young's assumption of an ever decreasing recession rate was flat out wrong. Garbage in, garbage out.

 

The reason the current recession rate is anomalistically high is the configuration of the continents. There are two huge north-south barriers to the tides, one from the southernmost tip of South America to the northernmost tip of Greenland, and the other from the southernmost tip of Africa to the northernmost tip of Siberia. That configuration is quite rare. At some times there was a more or less continuous path of ocean around the equator, which would have resulted in an anomalistically low recession rate. At other times, there has been one huge supercontinent, which would have presented but one barrier to the tides.

[krash661]

I know there will be a good answer but since I don't know it does anyone here?

 

On a Christian website the orbital distance of the moon has been compaired to it's rate of drift away from the earth. They have come up with the result that it must have been at mimum distance some 1.5 billion years ago. How are they wrong?

 

Here's the link;

 

http://creation.com/the-moon-the-light-that-rules-the-night

I lost interest once i read ,

 

" On a Christian website " .

[pwagen]

I lost interest once i read ,

 

" On a Christian website " .

Did you know the answer though? Yes, claims coming from creationists means they're almost certainly wrong or misinterpreted, but it's not always easy for lay persons to debunk these (erroneous) claims, as they often seem logical on the surface. Besides, there's hardly ever a bad reason for learning something new.

 

TalkOrigins.org has a small index with a handful of claims made by creationists, as well as why they're wrong.

http://www.talkorigins.org/indexcc/list.html

 

As for the Moon, specifically, which reiterates what D H wrote:

http://www.talkorigins.org/indexcc/CE/CE110.html

[Tim the plumber]

Thanks.

 

It's always facinating to understand something a little better. The idea that the arrangement of the land masses of the earth was the answer had definately never occured to me. I was thinking of asteroid impacts or something.

 

I'll get back to upseting those who wish to ignore the real world.

[Airbrush]

"The reason the current recession rate is anomalistically high is the configuration of the continents."

 

The configuration of the continents should block the Moon's tidal effects and SLOW down the Moon's recession rate. The reason I believe this is because of programs I've seen about the universe. In order for humans to slow down the Moon's recession rate, to preserve the beneficial effects the Moon has on Earth's climate, we should, in the future, build DAMS to block the tides EVEN MORE because tidal effects generally slow Earth's rotation and SPEED up the Moon's recession. So I think current configuration of the continents blocks the tidal effects (compared to ancient times) and act to slow the Moon's recession. Or am I wrong?

Edited April 25, 2013 by Airbrush

[Janus]

"The reason the current recession rate is anomalistically high is the configuration of the continents."

 

The configuration of the continents should block the Moon's tidal effects and SLOW down the Moon's recession rate. The reason I believe this is because of programs I've seen about the universe. In order for humans to slow down the Moon's recession rate, to preserve the beneficial effects the Moon has on Earth's climate, we should, in the future, build DAMS to block the tides EVEN MORE because tidal effects generally slow Earth's rotation and SPEED up the Moon's recession. So I think current configuration of the continents blocks the tidal effects (compared to ancient times) and act to slow the Moon's recession. Or am I wrong?

You have it backwards. It is the friction between the tides and the Rotating Earth that leads to the reccession. Basically, this friction drags the tidal bulge with the rotating Earth so that it leads the Moon a bit. the gravitational pull between the bulge and the Moon pulls forward on the Moon increasing its orbital energy, pushing it into a higher orbit. In response, the earth slows a bit in its rotation.

[Iggy]

"The reason the current recession rate is anomalistically high is the configuration of the continents."

 

The configuration of the continents should block the Moon's tidal effects and SLOW down the Moon's recession rate. The reason I believe this is because of programs I've seen about the universe. In order for humans to slow down the Moon's recession rate, to preserve the beneficial effects the Moon has on Earth's climate, we should, in the future, build DAMS to block the tides EVEN MORE because tidal effects generally slow Earth's rotation and SPEED up the Moon's recession.

 

If you significantly walled up the water then you wouldn't get the bulge that Janus is talking about. With no tides you'd have no friction from earth trying to spin its way free underneath them, so the program is right. That would slow the moon's recession rate.

 

If you imagine *no* equatorial obstacle, the recession rate is very low. As you add obstacles, the rate goes up. Eventually as you add more obstacles, and start trapping enough water, the rate will start to fall as you add more.

[Airbrush]

You have it backwards. It is the friction between the tides and the Rotating Earth that leads to the reccession. Basically, this friction drags the tidal bulge with the rotating Earth so that it leads the Moon a bit. the gravitational pull between the bulge and the Moon pulls forward on the Moon increasing its orbital energy, pushing it into a higher orbit. In response, the earth slows a bit in its rotation.

 

Thanks, that is what I now recall. So, in ancient times, were the continents configured to allow more tidal bulge to slow Earth's rotation faster than it is now or less? Or was there a series of increases and decreases in the motion of the tidal bulge as the continents shifted?

Edited April 26, 2013 by Airbrush

[Iggy]

Thanks, that is what I now recall. So, in ancient times, were the continents configured to allow more tidal bulge to slow Earth's rotation faster than it is now or less? Or was there a series of increases and decreases in the motion of the tidal bulge as the continents shifted?

 

If you don't mind me giving my 2¢ (it looks like Janus is unavailable). DH's post #2 is the standard wisdom. The recession rate is very high right now because of the unique configuration of the continents. The tidal bulge has to make its way around two large obstacles resulting in a lot of friction and transferring a lot of angular momentum from the earth to the moon.

[Airbrush]

If you don't mind me giving my 2¢ (it looks like Janus is unavailable). DH's post #2 is the standard wisdom. The recession rate is very high right now because of the unique configuration of the continents. The tidal bulge has to make its way around two large obstacles resulting in a lot of friction and transferring a lot of angular momentum from the earth to the moon.

Thanks Iggy. Suppose the Earth was a water world, with no land masses, and the oceans were very deep. Would that result in the highest rate of Moon recession and slowing of the Earth's rotation?

[Iggy]

 

Thanks Iggy. Suppose the Earth was a water world, with no land masses, and the oceans were very deep. Would that result in the highest rate of Moon recession and slowing of the Earth's rotation?

 

No, I'm pretty sure that should make for a very low recession rate. It obviously depends on other factors, but generally less friction means less slowing for earth's rotation.

 

Earth spins underneath the crest of the tidal wave that the moon creates. Earth's rotation pushes the tidal wave east and the moon pulls back on it from the west. If there are no land masses for the tidal bulge to bump into then the earth should have a pretty easy time spinning underneath the tides. There isn't much friction.

 

The friction you get when the tides move up onto land accounts for more loss to earth's angular momentum.

 

Another contributing factor could be that the speed of earth's rotation and the moon's orbit are in a resonance right now. Like pushing a person on a swing. You don't have to push very hard if you time it right they go very high. If things are timed right -- if the system is in resonance -- then the moon doesn't have to pull very hard on the tides to get a large effect.

[Airbrush]

No, I'm pretty sure that should make for a very low recession rate. It obviously depends on other factors, but generally less friction means less slowing for earth's rotation.

 

Earth spins underneath the crest of the tidal wave that the moon creates. Earth's rotation pushes the tidal wave east and the moon pulls back on it from the west. If there are no land masses for the tidal bulge to bump into then the earth should have a pretty easy time spinning underneath the tides. There isn't much friction.

 

The friction you get when the tides move up onto land accounts for more loss to earth's angular momentum.

 

Another contributing factor could be that the speed of earth's rotation and the moon's orbit are in a resonance right now. Like pushing a person on a swing. You don't have to push very hard if you time it right they go very high. If things are timed right -- if the system is in resonance -- then the moon doesn't have to pull very hard on the tides to get a large effect.

Thanks Iggy, that's what I wanted to know. Good answer, that deserves a bonus point!