Moon-o-lator 3
Here you can see the moving mask. When the cylindrical cutout lines up with the aperture, it's a full moon. At 90 degrees, it's a half moon. As it rotates further, the semicircular disc on the other side produces a crescent moon. Smart people will realize that this is only half the cycle! I'm totally cheating. To do the full cycle, one would either need another mask: a mirror image, but scaled to match the size of the beam at its location, or make a single mask that would rotate 180 degrees on a horizontal axis, during the full moon. Moon projectors are tricky. I learned that.
Moon-o-lator 3
Here you can see the moving mask. When the cylindrical cutout lines up with the aperture, it's a full moon. At 90 degrees, it's a half moon. As it rotates further, the semicircular disc on the other side produces a crescent moon. Smart people will realize that this is only half the cycle! I'm totally cheating. To do the full cycle, one would either need another mask: a mirror image, but scaled to match the size of the beam at its location, or make a single mask that would rotate 180 degrees on a horizontal axis, during the full moon. Moon projectors are tricky. I learned that.