sallyw@tekigm.UUCP (Sally Wagner) (06/06/84)
I want to know if the Moon actually rotates on its own axis? I have asked several people and find differing viewpoints. Some people say yes and some people say no. I thought this might be a good trivia question.
csc@watmath.UUCP (Computer Sci Club) (06/07/84)
Yes the moon does rotate on its own axis. However the moon always
keeps the same side facing toward the earth. This leads to the
confusion you have experienced.
To illustrate take two plates and a table. Put one plate in the center
to represent the earth. Mark one edge of the other plate, this is the
moon. Now revolve the moon about the earth without rotating it. (i.e.
move the marked plate in a circle around the unmarked plate while making
sure the marked edge of the plate always points to the same edge of the
table) You will note that the moon does not always have the same side
facing the earth. Next revolve the moon about the earth keeping the marked
edge facing the earth. You will note that as you revolve the plate once
about the earth, it will rotate on its axis (realative to the table) once.
This is the what the moon does. In order to keep the same side facing the
earth it must (relative to the stars) rotate once on its axis for each
revolution around the earth.
Hope I have not confused things even more.
William Hughesbenw@desoto.UUCP (B Weber) (06/08/84)
The moon does inded rotate on its axis...it just so happens that the period of rotation is exactly one earth day, so the same side of the moon always faces us. Try to picture the rotation of the moon from a point out of the earth-moon system; then try to picture it without the earth. The moon slowly rotates. Ben Weber ATTT
wetcw@pyuxa.UUCP (T C Wheeler) (06/11/84)
[] The Moon does NOT rotate on its own axis. Think about it. T.C. Wheeler
wetcw@pyuxa.UUCP (T C Wheeler) (06/11/84)
[] OK, OK, imagine a rope securely fastened to the center of the face of the moon facing earth. Extend that rope to one foot off the surface of the earth. IF the moon rotates, the rope will be wound up on the moon's surface. However, since it does Not rotate, the rope will remain one foot off the surface of the earth. Think about it. It is no different than many of our satellites which present the same face to the earth at all times. T. C. Wheeler
stekas@hou2g.UUCP (J.STEKAS) (06/11/84)
So, if one can hang a rope from the Moon to the Earth and it doesn't
coil up, that proves the Moon doesn't rotate. Then the Earth doesn't
rotate either. If it did then all the playground swings would get
wrapped around their supporting bars. Think about it. (:-)
Jimdarrelj@sdcrdcf.UUCP (06/12/84)
The moon does rotate with a motion which is distinct from its revolution
about the earth. (However the two motions are phase-locked by tidal forces
so they have the same period)
This independent (and essentially constant speed to conserve angular
momementum) rotation can seen because the eliptical orbital path of the moon
(about 10%) changes it's speed around Earth, so the rotation gets a little
ahead of and behind keeping one face toward Earth--thus we have earth based
photos of about 55% of lunar surface.
If you want to have the moon wind up a rope, run your rope to Mars. Earth
is not sufficently decoupled from the moon to be a suitable reference point.
--
Darrel J. Van Buer, PhD
System Development Corp.
2500 Colorado Ave
Santa Monica, CA 90406
(213)820-4111 x5449
...{allegra,burdvax,cbosgd,hplabs,ihnp4,sdccsu3,trw-unix}!sdcrdcf!darrelj
VANBUER@USC-ECL.ARPAbrad@looking.UUCP (Brad Templeton) (06/13/84)
And I had the impression that net readers had a slightly higher level of education than average! "The moon has no tangential velocity wrt its surface" (I hope this is a joke, Mr. Wheeler) For those of you who sill aren't sure. Say you look to your right and you see me looking at you. Now I move around to your left, so that I am still looking at you. Clearly I have rotated 180 degrees because I am now facing in the reverse direction. From the moon, the stars circle the sky once every ~28 days. (as does the sun, as even we can see from the Earth watching the light-dark line change) Just how does this miracle occur. No doubt the few of you in the dark ages claim that the sun and stars must go around the moon! I assume you will now tell me the Earth doesn't spin because communications satellites stay in the same place all the time, and we always present the same face to them! And how odd it is that by giving the moon some spin we would cause the stars to stop in the lunar sky! Remember heliocentrists, the moon does NOT orbit the Earth, they both orbit each other. There is nothing special about the viewpoint here. As I once heard it put, the Earth is a satellite in the Lunarsynchronous orbit (although that's a bit too far). -- Brad Templeton - Waterloo, Ontario (519) 886-7304
barmar@mit-eddie.UUCP (Barry Margolin) (06/13/84)
The argument about tying a rope from the moon to the earth doesn't hold water. If the earth end of that rope were moved to the sun then it WOULD end up winding around the moon. All you proved was that the moon keeps the same face towards the earth, which is well known. -- Barry Margolin ARPA: barmar@MIT-Multics UUCP: ..!genrad!mit-eddie!barmar