Some spectroscopes use prisms to separate light into its various colors. Others separate light with a diffraction grating, a film that has thousands of microscopic grooves lined up next to each other. Since a compact disc also has thousands of microscopic grooves, you can use it as a spectroscope to analyze light. It's best to do your light analysis at night when sunlight doesn't wash out your results. If you want to examine the spectrum of sunlight, use the moon as your light source so you won't damage your eyes (remember, the moon glows by reflecting sunlight).
You will need
What to do
Start by examining the spectrum of an incandescent bulb. Hold the CD in your right hand, about at your waist, and stand so that the light source you want to examine is off to your left. Rock the CD back and forth at an angle until you see a rainbow stripe in the disc. Closing one eye often helps.
To observe and notice
As you tip the CD back and forth, you should be able to see the entire spectrum -- red, orange, yellow, green, blue, and violet. If you have a dimmer switch on your incandescent bulb, see what happens to the spectrum as you dim and brighten the bulb. When it's dim, the red end of the rainbow will be more prominent. When it's bright, the blue end of the rainbow will be more visible. Stars are like the filament in the light bulb. As they heat up, they get brighter and bluer! Their spectrum can tell you their temperature.
Now use your CD to look at the light of a street lamp. Again, make sure the lamp is in the distance to your left and rock the CD in you right hand. Does the spectrum look the same as it did for the incandescent bulb? You'll notice that the rainbow of a streetlamp is not a continuous smear of red-orange-yellow-green-blue-violet light, but rather a line of separate, distinct colors. If the street lamp is a typical mercury vapor lamp, those colors will be: red, orange, green, and blue.
When different gases glow, they glow with their own unique set of spectral colors. Astronomers use these rainbow "fingerprints" to identify what gases and chemicals are present in stars.
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