🚀 go-pugleaf

Fabrikant wrote:
> 
> I have heard an interview with one scientist from a Research Institute
> in Boulder.  She claimed to have discovered the origin of the Moon.
> According to her, a huge asteroid of the size of Mars has collided
> with our Earth several billion years ago.  An explosion followed, huge
> cloud of matter was thrown very far away from Earth.  This cloud then
> condensed into the Moon, and this is how the Moon was created.
> 
> She also claimed that right after the collision, the Earth spin was so
> fast, that one revolution took 5 hours instead of 24.  The moon was
> originally much closer to Earth, and the distance is increasing by 3
> cm. per year.  The reporter, regretfully, did not know what question
> to ask.  Here are some questions, which I would like to ask.  First,
> how can she measure the distance between the Earth and the Moon with
> the accuracy of 3 cm? 

Laser light reflection from some reflectors conveniently left up there for
just this purpose about 30 years ago. Light travels at a known speed, time
of flight calculations reveal distance. Same principle as radar, more or
less. 

> Neither Earth, nor Moon are perfect spheres.

And what exactly has this got to do with anything?

> The distance between the Earth mountain to the Moon mountain is
> different from the distance between the Earth ocean to the same place
> on the Moon.  The Moon's orbit is not a perfect circle either, so I
> would ask her whether she was talking about the distance at a certain
> point in the orbit or whether she claimed the distance to be
> increasing all over the trajectory.  If it is all over, I would
> inquire, what forces produce such a change, and where does the
> necessary energy come from.

Try looking up "Roche" in the context of "tidal" and possibly you might get
better results and directly to your point by searching for "roche limit". 

> 
> There are no planets between the Earth and the Moon.  The planets from
> the outside can not possibly increase the distance between the Earth
> and the Moon, unless they attract the Moon and repulse the Earth, and
> such bodies just do not exist. 

Your understanding of physics is quite incomplete. Ponder the significance
of "inverse square law" in the context of "gravity". 

> The woman explained the slowing of the
> Earth rotation by the fact that distance between the Moon and the
> Earth was increasing.  My little brain can not find any law of
> Mechanics, which would relate these two phenomena.  Common sense tells
> us that the greater the distance between any 2 bodies, the less is
> their mutual influence.  I would have understood the argument that the
> tides, influenced by the Moon, can somewhat slow down its rotation,
> but again, with increase of the distance between them, this influence
> will decrease, not increase.

You're looking at it backwards. 

Look, Luna has already been tidally locked to Homeworld and so it cannot
lose any more energy by slowing rotation. The energy that it transfers to us
in the form of tides is energy that it no longer has locked into orbital
inertia. So, either the moon can lose energy and draw nearer the earth in
which case the tidal forces transferred are greater, or the earth can lose
rotational speed in which case the angular momentum of the locked system
redistributes out to the lunar node. If both earth and moon were solid
objects, the expected course of events would be that the lesser body would
eventually spiral in to the point where it either impacted the parent body
or was shattered by tidal forces or the parent body was shattered by tidal
forces or some combination of all of the above. However, the earth is not a
solid body and thus tidal forces can be redistributed throughout the fluid
mass. Factors such as internal drag and viscosity can cause the amount of
tidal energy in the fluid mass to balance the process so that net energy is
transferred to the lesser body, sufficiently so as to increase its orbit,
however slightly. Note that the drag in the fluid body has been sufficient
to reduce the earth's day from about 13 hours in the age of the dinosaurs to
about 24 hours in the present age. 

> 
> There is one more little detail, which the woman did not address.  The
> Moon rotates in such a way, that we always see only one side of it.  I
> just wonder, how "accurate" must be the blow to the Earth, which would
> not only create the Moon, but also make it rotate with such a
> remarkably accurate speed.

This is a phenomonon called "tidal locking". Two rotating masses in a common
orbit also orbit about one another and in terms of energies may be seen as
one system. The less massive of the two objects will always tend to lose
rotation before the larger, in proportion of course to the masses of both
objects and the initial rotational energies (speeds) of those respective
masses. Given the example of the moon and the earth both spinning at the
same speed, withthe moon having one sixth of the mass of earth, the moon
will yield rotational energy to be converted through tidal drag into orbital
energy; as it slows rotation it increases orbital speed and thus orbital
height. Once tidal locking occurs, tidal drag then slows the rotation of the
greater object, also slightly increasing orbital height since the two bodies
are effectively one system with a specific and finite amount of inertial
energy; energy moves from rotation into co-orbit. As the system experiences
tidal drag from the orbit around the primary (Sol), the combined system of
Sol and Luna/Earth maintains the same energy but the co-orbit of Luna/Earth
decreases rotational energy and thus the distance from Sol to Luna/Earth
increases slightly on average but the distance between Luna and Earth
decrease. Eventually one or the other or both bodies shatter due to
proximity and increased tidal forces and eventually most of the shattered
pieces coalesce into the same orbit, effectively becoming one body and
eventually gravity and heating will cause total coalescence into one uniform
body, perhaps with a lot of very minor moons in a co-orbit. 

I probably muffed some of the detail, but that's more or less how it works.


> 
> Fabrikant

-- 
    Be kind to your neighbors, even though they be transgenic chimerae.
Whom thou'st vex'd waxeth wroth:  Meow. <-----> http://earthops.net/klaatu/