From: trakar@comcast.net   
      
   On 9 Jul 2003 10:04:27 -0700, brdavis@iusb.edu (Brian Davis) wrote:   
      
   >   One thing he might have been talking about is the tidal evolution   
   >of the Moon moving it so far outward that the lunar orbit might become   
   >unstable due to solar perturbations. A simple esitmate of the   
   >tidally-locked end state of the Earth-Moon system predicts an   
   >Earth-Moon distance of around 93 Earth radii (it's currently about 60   
   >Earth radii out), and a "day" = "month" = 52 current days long. If you   
   >take the Earth's core into account, it's a little closer (a_final =   
   >86.4 Earth radii & "month" = 46.8 current days long), but it's still   
   >way out there. Earth's current Hill sphere limits the stability of   
   >orbits: roughly (i.e., empirically), orbits inside 1/3 a_hill are   
   >stable in a long term sense, while those outside are not. 1/3 a_hill   
   >for the Earth is about 78 Earth radii, so you're right on the edge of   
   >stability (probably beyond it).   
   >   To really figure out of the Moon would ever get outside that   
   >stability limit, you have to consider the time evolution of the system   
   >with both lunar & solar tides. It's not a case of one functioning at   
   >one time and a second mechanism taking over later, but a shift in   
   >dominance. And this shift may allow the Earth to retain the Moon.   
      
   I wish that it had been something of this level, and I was actually   
   open to some such discussion when I initiated the conversation.   
   However, he did not seem to understand the forces that were   
   responsible for lunar recession in the first place, initially claiming   
   that it was a mysterious, not understood phenomena (and I'm sure it   
   was from his perspective). Then he began trying to argue that the Moon   
   was just slightly above escape velocity and it was just slowly   
   climbing out of the Earth's gravity well. After verbally "ribbing" him   
   pretty hard (he's actually fairly informed about many things but I do   
   so enjoy finding these knowledge holes and hooking a finger in them!),   
   I went into some detailed discriptions of the general processes and   
   directed him to some websites and text books. I generally only catch   
   him on major things like this once or twice a year, mainly because he   
   pouts and sulks for a few months afterward, but hey, what else are   
   friends for?!   
      
   >> I had found several supporting sites, unfortunately I also found several   
   >> university sites that had misleading and even incorrect information up   
   >> on their websites,   
   >   
   >   I'd be *very* curious about these. Can you provide any URL's?   
      
   I've already contacted the sites I encountered, and even though I may   
   sound like a cold-hearted bastard, I'll give them a couple weeks to   
   address the issue before I start publically trashing them too hard   
   (besides it may have just been matters of my own misunderstanding of   
   their explanations---heaven forbid! ;)   
   The main mistake that I ran across was a conflation of orbital period   
   and velocity. The impression from the websites is that the object was   
   losing velocity or travelling slower and going into a higher orbit.   
   This is contradictory to my understanding of orbital mechanics. The   
   object in orbit gains velocity and moves to a higher orbit which takes   
   a longer time for it to complete a full orbit.   
      
   I would like to find the original papers I read discussing these   
   issues, but I read them many years ago, and have no idea who the   
   authors were. I slogged through search engine results for two days and   
   gave up. If any of this strikes a cord of familiarity in anyone, I'd   
   appreciate any helpful hints, tips, urls, university or professional   
   references, Thanks   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)