Question about space elevators:

Originally posted by FabianFnas
(1) The end of the cable must be way beyond the geo-stationary orbit. So the end of the cable has already a velocity way beyond the limit to be flung out from the earth. Just let it go and it will leave by itself. But the question I would like to know - how far out is the minimum distance from the surface will the space-lift reach? Theoretically with infi ...[text shortened]... otation is syncronized with the orbit of the moon, then it will be possible, but not until then.

Well, given the elevator cable, you could theoretically build a tower at the North or South pole, hook the cable to that then string it to the moon to ITS matching pole, I don't think there would be a conflict then.

In fact, it looks to me like if you did that at north and south poles of the moon, 2 cables could be used to generate power by the fact the moon moves closer and further from Earth.

Originally posted by sonhouse
Well, given the elevator cable, you could theoretically build a tower at the North or South pole, hook the cable to that then string it to the moon to ITS matching pole, I don't think there would be a conflict then.

In fact, it looks to me like if you did that at north and south poles of the moon, 2 cables could be used to generate power by the fact the moon moves closer and further from Earth.

Not even at the poles the moon is above horizon 24 hours a day, 365 days a year. But you know that before, didn't you?

Originally posted by humy
No it won't! That is because the Moon is orbiting around the Earth in the opposite direction from the direction of the rotation of the Earth around its own axis thus it will always appear to be moving around the earth from the viewpoint of any point on the Earths surface.

The term is "Tidal locking" or "gravitational locking" or "captured rotation" or "synchronous rotation". You can read about it at http://en.wikipedia.org/wiki/Tidal_locking

Today the moon shows the same side to earth during all its orbit. The Earth rotation, however, is not yet locked to the moon. In the far future it will.

Do you want to change your answer according to this information?

Originally posted by FabianFnas
The term is "Tidal locking" or "gravitational locking" or "captured rotation" or "synchronous rotation". You can read about it at http://en.wikipedia.org/wiki/Tidal_locking

Today the moon shows the same side to earth during all its orbit. The Earth rotation, however, is not yet locked to the moon. In the far future it will.

Do you want to change your answer according to this information?

Yes, I certainly already knew what tidal locking is.

The Moon is orbiting around the Earth in the opposite direction from the direction of the rotation of the Earth around its own axis. Therefore, the only way the Earth could become tidally locked with the Moon is if tidal forces eventually make the Earth first stop rotating and then start rotating in the opposite direction. But, before that time (hundreds of billions of years in the future ) , if the Earth and moon would still exist then, the Moon would have moved so far out from the gravity well of the Earth that its orbit around the Earth would have become unstable (interacting with the gravity of other planets and even that of the sun ) and would either be lost from the Earth's orbit or crush down to the Earth's surface!

However, well before that, the Earth and moon would most probability be swallowed up by the sun when our sun swells to become a red giant:

http://en.wikipedia.org/wiki/Future_of_the_Earth
"...
The most probable fate of the planet is absorption by the Sun in about 7.5 billion years
..."

So, for those two reasons, it would be highly unlikely that the Earth will ever be tidally locked with the Moon.

Originally posted by humy
Yes, I certainly already knew what tidal locking is.

The Moon is orbiting around the Earth in the opposite direction from the direction of the rotation of the Earth around its own axis. Therefore, the only way the Earth could become tidally locked with the Moon is if tidal forces eventually make the Earth first stop rotating and then start rotating in ...[text shortened]... o reasons, it would be highly unlikely that the Earth will ever be tidally locked with the Moon.

Seems that you have changed your opinion, and that's fine with me.

On the last posting I fully agree with you (possibly with the exception of hundred of billions of years).

Originally posted by humy
The Moon is orbiting around the Earth in the opposite direction from the direction of the rotation of the Earth around its own axis.

This is false, as I pointed out before. Both revolve in a counterclockwise direction when viewed from above Earth's northern pole.

Originally posted by FabianFnas
Not even at the poles the moon is above horizon 24 hours a day, 365 days a year. But you know that before, didn't you?

Well then, a VERY high tower?🙂

Originally posted by sonhouse
Well then, a VERY high tower?🙂

This is a math question from me to you, and I know that you are able to calculate the right answer:

How high does a tower at Earth's rotational pole need to be if, from the very top, you will be able to have a clear view at the moon 24 hours a day, 365 days a year, every year?

Originally posted by Soothfast
This is false, as I pointed out before. Both revolve in a counterclockwise direction when viewed from above Earth's northern pole.

Yes, you are right; my mistake.
I just tried to check and found this when getting a clue from the tidal period:

http://en.wikipedia.org/wiki/Tide
"...Its period is about 12 hours and 25.2 minutes
...
...
The lunar day is longer than the Earth day because the Moon orbits in the same direction the Earth spins...."

Don't remember where I heard that the Earth's moon orbits in the opposite direction to that of the earth's spin but I must have simply heard wrong.

Is someone saying that the moons orbit is retrograde?

Originally posted by FabianFnas
Is someone saying that the moons orbit is retrograde?

That is what I thought and that is what I in effect told you -but I was completely wrong. My apologies.

Originally posted by FabianFnas
This is a math question from me to you, and I know that you are able to calculate the right answer:

How high does a tower at Earth's rotational pole need to be if, from the very top, you will be able to have a clear view at the moon 24 hours a day, 365 days a year, every year?

OMG, not even close to what I imagined. The moon's orbit is 5.1 degrees off the ecliptic so a base in meters of about 384 million meters as the distance to the moon, the height looks like it wants to be an impossible 21,000 miles or 32 million meters. Good grief. Is that what you get? Over 20,000 miles?

Well, maybe not quite, looks like 21K -~4K, radius of Earth so only a mere 17,000 odd miles high. Solving from a reference of the center of Earth.

So it is impossible. If you could build an elevator on the north pole you could do a hook up but the elevator concept depends on centripetal forces to hold them in place and at the north pole, no centripetal forces available so I will put that particular dream back on the way back shelf🙂

Originally posted by sonhouse
OMG, not even close to what I imagined. The moon's orbit is 5.1 degrees off the ecliptic so a base in meters of about 384 million meters as the distance to the moon, the height looks like it wants to be an impossible 21,000 miles or 32 million meters. Good grief. Is that what you get? Over 20,000 miles?

Well, maybe not quite, looks like 21K -~4K, radius ...[text shortened]... no centripetal forces available so I will put that particular dream back on the way back shelf🙂

What it's inclination to the ecliptic plane is not interesting here. Think equatorial plane and redo the calculations.

Originally posted by FabianFnas
What it's inclination to the ecliptic plane is not interesting here. Think equatorial plane and redo the calculations.

If the moon were a point and its orbit were entirely in the plane of Earth's equator, you'd never see the moon from the north pole. Your line of sight would be parallel to the plane of the ecliptic,* assuming the Earth to be a slightly oblate sphere. Of course, the moon actually subtends an angle of about half a degree in the sky and there's atmospheric diffraction to account for.


*Well, nearly so, depending on how tall you are.

Originally posted by FabianFnas
What it's inclination to the ecliptic plane is not interesting here. Think equatorial plane and redo the calculations.

Here is an image of the earth moon system, it looks to me like it is showing the tilt of the moon's orbit to be 5.2 degrees with regards to the equator of Earth. That is close to the number I used. (5.1 degrees)

YouTube

Oh, I see, the equitorial is 23.5 degrees so it is even more impossible. Just looking at the tilt it is easy to see the tower would have to be more like 160,000 km high. Arrgg! So much for that idea.