Just thought i’d throw these out there since were talking about why the moons motions are the way they are…
There are some theories to the effect of the moon being a chunk of earth or a celestial body smashing in to the earth billions of years ago. Recently i read about this on a link from FARK.com. What originally intrigued my interest was that a very contraversial theorist on the origins of man, Zacharia Sitchin, had said something similair - but he got his information from ancient sumerian texts.
jbock220, there is a significant difference between one collision or near collision between a Mars sized body and Earth 4.5 billion years ago and a periodic planetary crossing within recorded human history.
I’ve read The Twelfth Planet. It makes an intriguing story from an uninformed perspective. However, he relies heavily on his own singular translations of ancient texts to suit his predetermined scenario.
One aspect that is singular striking to me - the absolute lack of any of this supposed superadvanced technology. We’re supposed to believe that this superadvanced alien race visited Earth, bringing all their technology so they could create some sort of resort world/mining colony, and yet they don’t manage to leave behind a single artifact of their mysterious and advanced materials and equipment? All they left behind was clay and stone, made by the humans who were here. Uh huh.
I am in my fifties. I first learned about tidal locking of the moon as a child when my father took me to the planetarium. I didn’t understand it. I read books on astronomy, came across the part about tidal lock. I didn’t understand it. I went to college, studied engineering, took the physics courses, learned about centripetal and coriolis; They even talked about tidal lock. I didn’t understand it. My ignorance festered for decades. Finally, I come upon a web page with a link to a story by Scylla. I discover The Straight Dope. Rooting around, my ignorance on the issue of tidal lock is vanquished. Now, I understand it.
poem by the housemaid of a famous 17th cen. astronomer, who had explained to her that we always see the same side of the moon:
“Oh, moon, when I gaze on thy glorious face,
Careening around through the boundaries of space,
The question has often come into my mind,
Will I ever gaze on thy glorious behind?”
One things missing from those articles: the moon went slower and slower, but then did it finally stop? Apparently not, since the moon isn’t a perfectly symetrical mass. If you watch an animation of the moon through one complete orbit, you’ll see that it’s rocking back and forth.
I wonder if the rocking motion is a leftover from when the moon made it’s final “complete turn” and was dragged backwards? Or maybe the final rocking motion died away long ago, and the one we see today is pumped by the slightly changing earth-moon diatance during each orbit?
Similar topic: years ago I saw a stereo-pair photograph of the moon in 3D. But it was dated in the 1940s, before space flight. How the heck did someone get a camera out in space in order to photograph the moon from a different angle than on the earth? Simple: they just waited for the moon itself to rotate a bit. In the above animation notice how “three-dee” the rotating moon appears! Two of those frames, if placed into a 3D stereo viewer, should produce an excellent 3D view of the moon with no 1940 secret government space flights needed.
bbeaty, I already covered that in my Report: See the last paragraph. The wobble (referred to as libration) isn’t because the Moon is asymmetric (in fact, that’s what causes it to lock in the first place), but because the Moon’s orbit is asymmetric.
Asymmetry doesn’t have much to do with locking, I think–unless you mean the asymmetry caused by the tide. Even if the moon were symmetric, tidal friction would have slowed it.
Yes, exactly. Because of the tides, it’s not rotationally symmetric. But asymmetry of the Moon itself isn’t responsible for the wobble (or at least, not the largest portion of it: I suspect that the Moon has many of the same sorts of tiny wobbles as the Earth).
I’ll have to defer to RM Mentock on that one, or someone else who knows what he’s talking about. I know that at least some of the Earth’s wobbles are related to the liquid ocean, which is why I hedged and said “many”. But I’d be very surprised if the Moon were completely free of odd little wobbles.
The obvious awkward little wobble is the one detected via laser ranging and which used to be ascribed to an impact on an historic timescale. In particular, it was supposed to be from the formation of the crater Giordano Bruno, as supposedly recorded by Gervaise of Canterbury in 1178. However, this hypothesis has recently come under attact. So what’s causing the observed wobble, if not that ? In his paper (pdf) on the subject, Withers’ comment is:
Now, in the post-Apollo era, it was often suggested that the lunar core might be at least partly liquid. However, there’s been a fair amount of new data from missions in just the last couple of years and I don’t know how much this has altered the theorising about the interior.
