A sundial that works by holography has been built by engineers at the University of Colorado in Boulder. Instead of telling the time from a shadow cast by the Sun, the sunlight projects a holographic image of the hour, depending on the position of the Sun in the sky.
A traditional sundial projects a shadow onto a surface, calibrated to account for the height of the Sun at that particular latitude, including its seasonal variation.
The holographic sundial takes advantage of the way holograms store images: the image is recorded by a single laser beam split into two parts - one reflected back from the object, and the other serving as a reference. These are combined on a photographic plate. Light striking the developed hologram at the same angle as the reference beam, projects an image of the object. Multiple holograms can be recorded on one photographic plate and the ...
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