Using the ruler and pen, divide the bottom of the cardboard tube into eighth sections. Each section will contain one moon phase. Shade in the portion of the moon that would be lit if you were looking at it in the sky.
Use the box cutter to cut out the shaded portion of the moon phases you drew. After you have cut out all of the moon phases, cut a small hole in the center of the cardboard tube. Make sure the hole is large enough for the screw to fit through.
Place the end of the cardboard tube on your cardstock and trace around the outline to create a light block. Add a 2-inch rectangle to the edge of your circle. Divide the circle into eighth sections. Then cut out the circle and attached rectangular tab. Then cut out the section of the pie that is across from the tab, but do not cut all the way to the center of the circle. You need to leave about 1/4 inch of room at the center to punch a hole for the screw.
Now Punch a hole in the center of your circle and then place your light block on the end of your canister on top of the cut-out moon phases. Slide the screw through the hole in the light block and then through the tube. Attach the wing nut on the opposite end of the screw, inside the cardboard tube. The tab should slide the light block easily around the end of the tube.
Place your flashlight centered on the plastic top to your cardboard tube and trace the outline with a pen. Cut out the hole you drew and feed the top of your flashlight through the hole. Fasten the top with the attached flashlight back onto the open end of the cardboard tube, leaving the handle portion of the flashlight outside of the tube. Use paint, stickers, stencils, ribbon or markers to decorate the outside of the moon phase viewer tube.