[Squeakland] sun-earth-moon

[Randy Heiland]

Is it possible to squeak planetary motion?  Obviously, you can rotate the
earth about the sun by repositioning the earth's rotation center to the
center of the sun, but what about moving the moon about the (rotating)
earth?  If a sketch's rotation center had its x,y location exposed as tiles
then there could possibly be an elegant solution, but otherwise...?

While conducting another workshop with the Girl Scouts last night, Charlie,
my co-worker, came up with another scheme which I liked, to approximate
circular motion.  It consisted of:
  earth turn toward sun
  earth turn by 90
  forward 

I liked this idea of a simple "tangent" and, if it worked as hoped, you
could extend it to the moon-earth too.  However, we see that it's not
exactly an "instantaneous tangent" :)
http://poincare.uits.iupui.edu/~heiland/squeak/planets 

Ideas?  Thanks, Randy

Btw, I had a quick look at Randall Caton's excellent Squeak pages,
http://www.pcs.cnu.edu/~rcaton/extrasolar/students.html , but didn't see
anything that addressed this topic -- or maybe I just didn't dig deep
enough.