[Phys-L] earth orbiting around the moon, or not

[John Denker <jsd@av8n.com>]

Hi Folks --

I made a little movie.  It is based on the following premise:
Each month, the moon goes around in its orbit.  Specifically, 
it orbits around the center-of-mass of the earth/moon system.

The same goes for the earth: As you might expect based on 
the third law of motion, the earth also orbits around the 
center-of-mass of the earth-moon system.

Here's a two-minute movie that shows how that works:
  https://www.av8n.com/physics/earth-moon-spin-orbit.htm
or equivalently
  https://www.av8n.com/physics/earth-moon-spin-orbit.htm

I find it amusing to watch.

There's also a few hundred words of discussion, including
how to estimate where the center-of-mass is.

All this is brand new and probably full of typos.
Comments and suggestions are welcome.

The source code that makes the movie is online.