Homemade Spectroscope


  • Empty paper towel roll
  • Craft knife or scissors
  • Blank or old CD
  • Pencil
  • Small piece of cardboard or cardstock
  • Tape
  • Paint (optional)


  1. If you want to decorate your paper towel roll, do that first and let it dry.
  2. Use a craft knife to cut a slit near the bottom of the toilet paper roll. Make sure it is at a 45° angle.
  3. Cut out a small rectangle directly behind your slit. This will be your peephole.
  4. Use the end of your paper towel roll to outline a circle on your cardstock. Cut it out.
  5. Cut a thin rectangle in the middle of your circle.
  6. Tape the circle to the top of the paper towel roll.
  7. Put your CD into your slit. Make sure the shiny side is facing up.
  8. Go outside and look through your peep hold. You should see a rainbow!


When the sun shines down on us, it sends every color together in what is known as white light. White light is made up of many colors with different wavelengths and frequencies, but unless they are separated, we can’t see them all. This is where the CD comes in. It may look and feel smooth, but it actually has tiny ridges where the light will diffract off of. Diffraction is the spreading and separation of light. Because the colors all have different frequencies, they will diffract at different angles and a rainbow will be seen!