Re: Moon's synchronism

[Leigh Palmer <palmer@sfu.ca>]

> How long after the earth's rotation becomes synchronous with the moon will
> it become synchronous with the sun?

Considering the three-body case only one would not expect that
to happen in the age of the universe. The only* dissipative
mechanism left in the system is tides raised in the Sun by the
Earth-Moon system. Since the Sun now rotates once a month,
these tides will tend to push the Earth-Moon system farther
from the Sun. The interaction is so weak, however, that this
is a negligible effect, utterly unmeasurable even if there
were not more planets around with more influence. On the other
hand, the slowing of the Earth is quite measurable. It has
resulted in a retardation of about thirty degrees of rotation
over a period 1500 years relative to where the Earth would be
had there been no tidal slowing. The immediate consequence of
this is that, had the Moon not been there, you would have been
two hours late for every appointment you've had in your
lifetime for which you thought you'd been on time!

(Adapted from the chapter (XV?) "Cutoffs and Stephen" from
"Life on the Mississippi" by Mark Twain. See also "Gravitation"
by Misner, Thorne & Wheeler, p.25, Fig. 1.8.)

Leigh

*Well, OK, gravitational radiation too.