To use a cylindrical cardboard box to projecting images of star constellations onto the wall and ceilings of rooms.
Find a star chart in a books on astronomy or in an encyclopedia. Then copy the constellation you wish to project onto a sheet of thin paper. Then place the drawing face down on the outside of the bottom of the cylindrical box. Make sure that you are able to see the star-dots through the sheet of paper. With a nail, pierce holes through the cylindrical box at each dot so that the holes form a mirror-image pattern of the constellation (they will appear normal when projected).
To use the planetarium, take it into a dark room and insert a flashlight into the open end. Tilt the flashlight so that it shines against the sides of the cylindrical box, not directly towards the holes. This will throw an magnified image of the constellation onto the wall. By rotating the box you can project all positions of the star constellation.