Crystals May Have Aided Viking Sailors

Vikings may have used special crystals called sunstones to ensure gloomy weather did not come between them and an outing to sack British villages or discover new lands to the west, scientists have discovered. Tests aboard a research vessel in the Arctic ocean found that certain crystals can be used to reveal the position of the sun, a trick that would have allowed early explorers to ascertain their position and navigate, even if the sky was obscured by cloud or fog. The finding adds weight to the controversial suggestion that the Vikings exploited an unusual optical property of crystals known as birefringence to stay on course during bad weather.Researchers led by Gabor Horvath at Eotvos University in Budapest spent a month recording the polarisation of sunlight while at sea. Although polarisation is not apparent to the naked eye, it can be seen using birefringent crystals. The researchers found that the crystals were likely to work in all but the worst weather conditions, they write in the journal Proceedings of the Royal Society today. Professor Michael Berry, a physicist at Bristol University, said: "They've shown that even if the sky is full of clouds and moisture, the polarisation of the sunlight doesn't change very much, and that's a real surprise. If you know the time already, then once you know the position of the sun you know what direction you're sailing in."