Place the orange foam ball in the center of the cardboard plate to represent the sun.  The small yellow ball (the moon) with the slit in it can be placed anywhere along the edge of the plate.  The green ball can be used to represent the Earth.  With this equipment you can now show that no matter what the orbits, there are only two times when all three objects have a collinear alignment for an eclipse.

Put the Screw in Globe Light source on the large plate at one end of the optics bench.  Put the cardboard screen at the other end with the ball on the wire in the center of the bench so that you can move it to and away from the light source.  Observe the shadow on the screen. In the larger lecture rooms you will have to show the shadows with the camera.

The earth, moon, sun demo can also be used to show an eclipse.  Note that the best times to get an eclipse with this model is when the Earth is straight up and down.  This usually is only done in small class rooms as the shadow is very small.