[extropy-chat] Astronomical question

[Ian Goddard]

--- Mike Lorrey <mlorrey at yahoo.com> wrote:

> >  That process wont continue indefinitely. What's
> > happening is that the earth/moon system is slowly
> > "gravitating" toward synchronous rotation, or
> > tidal lock. 
> 
> I understand this. My question is whether the moon
> will accomplish this before becoming an independent 
> body or not.


 The moon's motion away from the earth is just a
process of distributing angular momentum in the
earth/moon system. So provided there are no other
forces acting on the moon I see no reason to assume
this feature of the process of achieving synchronous
rotation would eject the moon from the system. 


I wrote:

> Once the earth/moon system has reached synchronous
> rotation, or orbital stability, it's my 
> understanding that the earth/moon-system-induced 
> changes in question (earth slowing & moon 
> recession) will be stabilized.


 The Oxford Dictionary of Astronomy confirms that the
earth/moon process eventually stops, and adds some
interesting details that address long-term results:

"Over long periods of time tidal friction [induced by
the moon] decreases the Earth's rate of spin, so
lengthening the day. In turn, the Moon has angular
momentum added to it in its orbit and gradually
spirals away from the Earth. Ultimately, when the day
equals the Moon's orbital period (each being about 40
times the length of the present day) the process will
cease. A new process will then begin in which the
Sun's tide-raising power takes angular momentum from
the Earth-Moon system. The Moon will then spiral in
closer to the Earth until it is torn to pieces when it
enters the Earth's Roche limit." (page 461)

~Ian




		
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