Re: moon's synchronism

[Jim Riley <jriley@lib.drury.edu>]

At 03:34 PM 3/20/98 -0700, you wrote:
>

> Yes, components of the total Moon/Earth angular momentum MAY be chosen as
> above.
> BUT does that total angular momentum need be conserved ? -- indeed  isn't
> it clearly NOT  conserved? -- aren't there external torques applied to that
> system? 


> Jim Green
> JMGreen@sisna.com
>
> http://www.sisna.com/users/jmgreen
There probably is a torque on the earth moon system produced by the sun due
to the fact that the moon's orbit does not lie in the plane of the earth's
orbit.  My assumption (which may well not be correct) is that that torque is
small.  A still smaller torque might be produced by the effects of Jupiter
on the system.  My assumption (which again may not be correct) is that that
is also a small torque.  Even smaller torques are produced by the
gravitationalk effects of the other planets.  Thus my first approximation is
that the moon-earth system constitutes one with negligible external torque
and therefore has a constant total angular momentum.

Now that I think about it some more the sun ought to produce a torque
affecting the moon's orbital angular momentum which should cause its orbital
axis to precess around a line perpendicular to the earth's orbit.  I have no
idea of the period of that precession.
Jim Riley
Department of Physics
Drury College
Springfield Missouri  65802
(417) 873 7233
e-mail:  jriley@lib.drury.edu
fax: (417) 873 7432