Re: moon's synchronism

[Leigh Palmer <palmer@sfu.ca>]

> On 24 Mar 1998 11:17:29 Leigh Palmer <palmer@sfu.ca> wrote:
>
> > ... "Another torque acting on the Moon's orbit is due to the quadrupole
> > moment of the Earth"... I should have mentioned that it is the reaction
> > to this torque, the torque exerted by the orbiting Moon on the Earth,
> > that is partly responsible for the precession of the equinoxes. The
> > Sun is responsible for a smaller but significant contribution to this
> > precession.
>
> 1) Can it (librational shaking of the Earth) be also responsible for
>   other things, such as motions of tectonic plates, volcanos and
>   magnetic reversals?

I don't know. The shaking is quite gentle, and the monthly periodicity
is so far from the precessional frequency (~10^-12 Hz) that one integrates
over it, so the motion could hardly be characterized as a libration.

> 2) A nice way of referring to librations of the Moon is to say that they
>   exist because the center of mass of that large spherical object does
>   not coincide with its center of weight. The center of weight is closer
>   to the Earth than the center of mass. To keep it simple I am thinking
>   about an ideal circular orbit.

I'm afraid I don't quite see that, Ludwik. So far as I know there's
no such thing as "center of weight". It sounds suspiciously like the
old "center of gravity" that took such a long time to disappear from
the literature.

> 3) Librations of the Earth would be "as strong", and would have the same
>   period, as librations of the Moon if the two objects had identical
>   masses. But the mass of E is about 80 times larger than that of M.

?

Leigh