Still working on this one, sorry!
You can google pinhole projection, it is rather straightforward. Just make a little hole in a piece of cardboard—it will work even if it is not round—and it will project a little Sun on a flat surface. It happens all the time in nature, only we don't notice because the Sun is just round.
See this nice pinhole projection image, learn more about how to do it here, and see the classic skimmer projection here.
Very cool scheme for efficient pinhole projection. Blame this guy and his quaint website.
Come to think of it, the page is about done now!