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What is the period of libration of the moon? I want to compare this with
what I simulated for two rigidly connected half-moons. What fraction of
the "projected circular face" keeps hiding from us periodically? I guess
I can check it myself with a pair of binoculars but learning it from
somebody who already knows will save a lot of time. (Both Igal and Leigh
would probably agree, in this particular case).
Another thing I learned under this thread (please confirm or contradict)
is that the disipation of mechanical energy (frictional solid tides)
is not necessary to explain librations.
I also learned about the two meanings of the word libration. The first
has to do with lunar face changes, the second is more general. According
to my reference, "it signifies that a particle at the libration point is
in balance, at rest in the rotating frame, the centrifugal forces and
the gravitational pulls of the two larger bodies just canceling". (In
"Celestial Encounters", by Diacu and Holmes, Princeton University
Press, 1996). Libratio means balance in Latin. Five Lagrange points
are equilibrium points when a small satellite is in motion in the field
created by two much larger objects. The satellite has a negligible effect
on the motions of large objects. I know this was already discussed here.
Forgive me if I am wrong by assuming that I was not the only one who did
not know what it was about.
Would you excomunicate me if I admit that I have no idea what a Klein
bottle is for? I resisted another "what is it?" reply when the Jack's
message appeared because I hoped to learn from what follows. No help
so far. Am I the only one who is so ignorant?