Vikings used crystal 'sunstones' to navigate the oceans

LEGENDS of marauding Vikings using magic stones to navigate the high seas are based in fact say researchers, who claim that, long before the invention of the compass, the warriors used crystals to help them sail during fog and cloud.

Norse seafarers are believed to have travelled from Scandinavia as far as North America, centuries before Christopher Columbus, and Norse Sagas talk of 'sunstones' that enabled them to pinpoint the position of the sun when it was not visible.

A new study claims these navigational aids really did exist and were made of a special light-fracturing crystal known as Iceland spar, which "depolarises" light down different axes. A single dot on the top of the stone would appear twice when viewed through the crystal, and the dots could be used to pinpoint the sun in fog and cloud.

Guy Ropars of the University of Rennes in Brittany, who oversaw the research, explained how it worked to AFP. "You rotate the crystal until the two points have exactly the same intensity or darkness. At that angle, the upward-facing surface indicates the direction of the Sun," he said.

The technique works even in thick cloud and at twilight and can determine the position of the sun to within a single degree.

It goes some way to explaining the mastery of the oceans that the Vikings had. Perpetual daylight in the summer months would have stopped them from using the stars to navigate and Scandinavian and North Atlantic waters are often covered in fog and cloud.

Iceland spar was also discovered aboard an Elizabethan ship that sank in 1592, suggesting that sunstones may have still been in use then.

The Vikings are not the only seafarers to have used unusual techniques to navigate the oceans. Ancient Polynesian voyagers were able to tell how far they were from land by sensing the reflection of waves bouncing off islands many miles away.

The team's findings are published this week in Proceedings of the Royal Society A: Mathematical and Physical Sciences. ·