Re: Planetary Motion Computation

First, it is very hard to have .999999 accuracy when it comes to planetary
positions and velocities.  We tried to construct a computer specifically for this
purpose.  We used seven pentium 75 computer boards (the best available at the
time) linked with big jumper cables.  Each computer was responsible for one planet
and we did not include Mercury, which does not seem to have that great an impact
on Venus, and we did not include Pluto.   Each computer fed its calculations
through the cables to the two adjoining computers, Saturn effected Jupiter in one
direction, and Uranus in the other, and all of these were then fed back through
the loop.  The sun's effects were programmed into each machine independently and
then the sum of the seven machines were fed into the sun's position.

The thing ran.  That was the first task and that took months.  We found that it
was very difficult to get the monster to spit out positions in four dimensions
with any greater accuracy than we were getting from more simple, one-machine,
programs.  There seemed to be a "chaos" factor that constantly slipped in and
caused the positions to fall out of agreement with the actual observed positions.
The observed positions were fed to us from a variety of sources.   So there you
have it.  We developed the "law of commulative abstractions" to describe what was
going on.  All the observations have a built in degree of fuzziness, and all of
the calculations are fuzzy as a result, plus there are many places where the level
of inaccuracies exceed the level of the math.   There are many places where the
level of accuracy is not that great, the mass of Jupiter is not known to the same
level of accuracy as the mass of Earth for example.  Thus as the system feeds into
a loop the inaccuracies of one measurement begin to feed into the model more and
more.

We thought at first that we would get some kind of grand equation that would say:
If Jupiter is here, and the Sun is here, and Uranus and Neptune are here, and the
Earth and Venus are here and here, then HERE is where Mars has to be.  That did
not happen.   I guess I just want to caution people that want to make assumptions
about planetary positions and perturbations that it is not at all simple to do.
That there are so many interdependent feed-back mechanisms at work that a simple
deduction based on a few variables is not going to be accurate at all.

Joax <[email protected]>

Bill Nelson wrote:
> In sci.astro josX wrote:
>>>
>>> This behaviour will continue: both planets will move to eachother everytime
>>> they come closest, until they crash. Since Saturn will be on a more outward
>>> orbit, and Jupiter on a more inward one, bringing them closer, increasing
>>> the gravity force, the crash wouldn't take much time either (i think)!
>
>> I will have to correct myself here: if Jup. is pulled in and Saturn
>> pulled out, they asume new ellpitacal orbits, now if they meet again,
>> both in their new orbits where they are just moving apart from eachother
>> (Jupiter outward/Saturn inward), the new perturbation will perhaps cancel
>> the earlier perturbation out.
>
> The planets are NOT "pulled inward" or "pulled outward". The gravitational
> attraction of the Sun is too great to allow that. What happens is that the
> planets change their orbital velocities slightly. This causes the orbit to
> move inward and outward - with the net change in orbital radius being zero.
>
>>> Maybe all planets are on this kind of an equilibrium?
>
>> It would still be an unstable equilibrium though, when planets are
>> going to crash, there is nothing to stop it; in fact, the attraction only
>> increases, speading the crash up.
>
> Planets are not going to go into unstable orbits - unless some very massive
> object arrives to perturb them.