## Part 0: A little geometry

You're going to be doing a simple animation that looks something
like a moon orbiting a planet which, in turn, orbits a sun.
Just 'cause I don't want you to get caught up worrying about the
trig of calculating positions in this scheme, the diagram to the
right shows how to do it. If you know the coordinates of your
"sun", P0 = (x0,y0), you can calculate the coordinates of your
planet when it's at angle a0 in its orbit, P1=(x1,x2). Then, when
the moon is at angle a1 in its orbit around the planet, you can
calculate its position P2=(x2,y2) from P1 and a1.

## Part 1: Circles

Your first job is to make this:

## Part 2: Animate

Your next job is to augment your Part 1 program so that pushing
the start button starts an animation in which the pink point
travels around the pink circle which, since the blue circle is
centered at the pink point, means that the blue circle travels
with it, while at the same time the blue point travels around the
blue circle. To "move" these points, simply keep adding some
small fixed amount (e.g. 0.01 to the inner and 0.04 to the outer)
to the angles (a0 and a1 in the diagram).

## Optional Challenge : stopping and restarting

See if you can modify the program so that once started, the button
label changes to "stop", and clicking it again stops the
animation, and returns the button label to "start". Clicking
again should start the animation again, and so on.
## Optional Challenge : tracing

See if you can modify the program so that the path of the dot
moving around the blue circle is taced out on the screen.
Like this :

## Submission

Demo this lab to your instructor rather than submit it via the
submit system.