Custom WHOI Classic Seal Spectral Sundial

This custom WHOI logo Spectral Sundial uses an audio Computer Disc (CD) to tell time! A great gift for any ocean lover and science geek.

How it works:
The audio CD is constructed using a thin polycarbonate disc. The disc spiral tracks are imprinted on its back side which has a reflective aluminized layer sputtered over it. The data tracks are separated at about 1.52 micrometers. The data tracks are about 0.8 micrometers wide. The combination of the tracks and reflective surface act as a ruled grating as used in commercial spectrographs. Thus, sunlight reflected off the CD will be shown as a spectrum of color. However, the use of the CD has one important feature not available when using a parallel ruled grating. Since the CD is a circular grating, the diffracted light is focused into a highly concentrated line of spectral colors. This makes the CD especially useful for use in a sundial.