The sun beams down on a tiny glen in Pennsylvania's Pocono Mountains-a radiant afternoon for an outdoor wedding.

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Find this orientation by looking through the crystal at the sky at a time when you can see the sun, mark the sun's direction on the crystal, and your mark will always point towards the sun when you match the beams from even a tiny patch of blue in an otherwise overcast sky.

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Testing a similar crystal, the scientists proved that by rotation it was possible to find the point where the two beams converge - indicating the direction of the Sun.

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