1861 Activity: Use a compact disk to make a spectroscope

The first spectroscopes used a glass prism to break up light into its constituent colors. An alternative technology for revealing the colors in light is a diffraction grating, which is a clear or reflective material with finely ruled lines. Diffraction gratings were invented around 1785 in Philadelphia by David Rittenhouse, but were initially difficult to produce. Now they can be found everywhere in the form of compact disks (CD). The “Cool Stuff” website describes how to make a simple spectroscope using a CD as follows:

  1. Cut a slit in one end of a shoebox top
  2. Cut a viewing port in the opposite end of the shoebox about 3/4" square
  3. Tape a CD with colorful mirrored side up at an angle under the slit.
  4. Point the slit at a light source and view the colors from the light source
Compact Disk.

Observe the smooth rainbow of colors from an incandescent light bulb and compare it with the lines at specific colors that come from a fluorescent light. Stars have both types of spectra. The smooth spectrum of colors indicates the average temperature of the star at its visible surface, while the bright lines reveal the composition of the star. Further information on this activity is available at: