From: jturner@tartarus.uwa.edu.au (Joseph Turner)
Newsgroups: comp.binaries.apple2
Subject: Planet motion
Date: 10 Jan 1997 14:44:04 GMT
Organization: The University of Western Australia
Message-ID: <5b5kjk$dfa$1@enyo.uwa.edu.au>


Hi, Just got a bit of inspiration today and wrote a quick litle program
that can be looked at on any appleII. This is no amazing program just
alittle thing that can be plaed with. I basically have tried a planet
simulation, i.e. The sun, then, the Earth and another planet or sun
further out from the Earth. Infact one can just consider it as being a 3 
body situation in the reference frame. What it basically does is plots
the obit of the earth around the Sun which is located at the centre of
the screen(note this isn't drawn in). The Other planet or sun further
out from the earth is not drawn in, but is still moved around in the
calculations. 
The program is written in basic and is quite small. Simply unbinscii it
and run it.

The variables with a one at the end(a '1') are for Earth and the ones
with a '2' at the end are for the outer planet. i.e. r1 = Radius of
planet Earth, m2 = mass of Outer planet, and M = mass of inner body.
All the units are in SI units, e.g. seconds, metres..etc.

To muck around with the program in an interesting way you can vary the
mass of the outer planet to see how it affects the motion of planet
Earth. This can be done by altering the mass of it on LINE 80 by telling 
the program how much more massive or smaller it is compared to the sun.
One thing That must be noted is that I have assumed the perturbation
effects on the outer planet are neglible to the motion, so only
perturbation affects have been taken in to account on the planet Earth.
So the mass pf the outer planet must be serveral orders of magnitude
greater then the mass of the Earth for the program to be sensible.

Another parameter that may be useful is the time between calculations.
This is on line 190, and the units are of course in seconds. For slower
computers just increase it. Not that by increasing this value you make
the output less accurate.

Ok, Maybe I should have said this at the beginning...I am not sure how
Accurate and exact this is(Not 100% sure this program is infact right)
but it looks like it is, and can't see any obvious errors...) so if you
see anything majorly wrong or have some input give it to me and I might
try to improve it. I will muck around with it a bit more some time later 
to improve it.

Ok hope you like it. 

Cheers
Joe
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AkCU
-- 
****************************************************************************$
     Joseph Turner
     Apple IIgs User, 1WSW Team Member and proud of it.
         
         Support the AppleII and make it   ___APPLE II For Ever____  
****************************************************************************$