the moon. again

[DutchE]

i asked when you think the moon stopped spinning. well i think it was 65 million years ago.

[blike]

but the moon is spinning. just not relative to us.

[wolfson]

Yep Blike has it there.

[DutchE]

i mean, as it is today, tidally locked. but when did it lock?

[Sayonara]

Isn't it the tides that are lunarly locked?

 

It made me laugh.

[gene]

The moon is spinning all the time, isn't it?

We still have tides. Don't we?

 

[Skye]

I think DutchE means when it stopped spinning relative to us.

 

From this site:

 

"The Earth's rotation carries the Earth's bulges slightly ahead of the point directly beneath the Moon. This means that the force between the Earth and the Moon is not exactly along the line between their centers producing a torque on the Earth and an accelerating force on the Moon. This causes a net transfer of rotational energy from the Earth to the Moon, slowing down the Earth's rotation by about 1.5 milliseconds/century and raising the Moon into a higher orbit by about 3.8 centimeters per year. (The opposite effect happens to satellites with unusual orbits such as Phobos and Triton).

The asymmetric nature of this gravitational interaction is also responsible for the fact that the Moon rotates synchronously, i.e. it is locked in phase with its orbit so that the same side is always facing toward the Earth. Just as the Earth's rotation is now being slowed by the Moon's influence so in the distant past the Moon's rotation was slowed by the action of the Earth, but in that case the effect was much stronger. When the Moon's rotation rate was slowed to match its orbital period (such that the bulge always faced toward the Earth) there was no longer an off-center torque on the Moon and a stable situation was achieved. The same thing has happened to most of the other satellites in the solar system. Eventually, the Earth's rotation will be slowed to match the Moon's period, too, as is the case with Pluto and Charon."

 

I guess the moon has always been rotating at around the same rate relative to earth.

 

[edited to include the italicy bits]

[blike]

Sayonara³ said in post #5 :

Isn't it the tides that are lunarly locked?

 

It made me laugh.

 

The moon has tides too. The term "tidally locked" is commonly used for a body that has the same rotation as its orbital period. Apparently, many bodies in the solar system are "tidally locked".

 

See: http://www.faqs.org/faqs/astronomy/faq/part5/section-20.html

 

Eventually, both the earth and the moon will be "tidally locked", and the moon will be locked in one position in the sky.

 

As to the original question, I will see if I can find something for you on google.

[DutchE]

:

 

:

 

"The Earth's rotation carries the Earth's bulges slightly ahead of the point directly beneath the Moon.

the gravitational explination would call for the bulge to be pointing at the moon, but i don't think it does.

i got a tidal predictor and looked at the tide of a place on the meridian line at midnight at a time of full moon. the moon didn't point at high tide but low tide. therefore, i don't believe in the gravitational model for tides

[Cheetah]

So are all moons locked to the celestial body they orbit? So that one side is always turned against the planet?

 

On my second thought. That can't be true, as wouldn't the planets orbiting the sun also only show one side against the sun at all times?

[blike]

No, not all bodies are. It depends on how long they've been in orbit. Eventually, the earth will orient toward the sun (assuming its around long enough).

[VendingMenace]

actually, the tidal forces the moon exerts on the earth are stronger than the ones the sun exerts on the earth. So first, the erath will stop spinning with respect to the sun (ie. same side of eart will always face the sun. Then, eventually, both the moon and the earth will be titally locked to the sun, with the earth and moon always in the same position to the sun (and at the same time in the same position to themselves).

 

But that will take awhile to happen, so don't worry about buying up all the good real estate yet

[jordan]

Since it has been established that time will cause "tidal locks", what is it that would cause this to happen?

[blike]

take a look at some of the links above. they explain the effect quite well.

[Sayonara]

blike said in post #8 :

The moon has tides too... etc

sayonara said in post #5 :

It made me laugh

 

n/m

[apollo2011]

I believe the correct term is "Synchronous" the moon is moving in synchronous to us so we only see one side. The other side is known as the dark side just because we never see it. It still gets light though.

[aman]

If we sped up the moons spin so its rotation reached near its escape velocity, then we could easily land on it and take off using hardly any fuel since we'd be weightless at the equator. Also mining would be simpler.

We just need to wind a big cable around the equator like a toy top and anchor it to a passing asteroid. Pull that string and watch that moon spin.

Just aman

[apollo2011]

Nice idea aman. That would really be a sight to see!

[Dave]

And somewhat of an engineering feat, be quite interesting to watch though

[apollo2011]

And we could probably see it from here too.

[Sayonara]

Yes, we could appreciate mankind's mighty control over every force of nature whilst... OH MY GOD IT'S COMING RIGHT FOR US!