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Telegraph UK A Viking legend which tells of a glowing "sunstone" that, when held up to the sky, disclosed the position of the Sun on a cloudy day may have some basis in truth, scientists believe. 
The ancient race are believed to have to discovered North America hundreds of years before Christopher Columbus. Now experiments have shown that a crystal, called an Iceland spar, could detect the sun with an accuracy within a degree allowing the legendary seafarers to navigate thousands of miles on cloudy days and during short Nordic nights. Dr Guy Ropars, of the University of Rennes, and colleagues said "a precision of a few degrees could be reached" even when the sun was below the horizon. An Iceland spar, which is transparent and made of calcite, was found in the wreck of an Elizabethan ship discovered thirty years ago off the coast of Alderney in the Channel Islands after it sank in 1592 just four years after the defeat of the Spanish Armada. Viking legend tells of an enigmatic sunstone or sólarsteinn that, when held up to the sky, revealed the position of the sun, even on overcast days or below the horizon, the study reveals. One Icelandic saga describes how, during cloudy, snowy weather, King Olaf consulted Sigurd on the location of the Sun. To check Sigurd's answer, Olaf "grabbed a sunstone, looked at the sky and saw from where the light came, from which he guessed the position of the invisible Sun" Using the polarisation of the skylight, as many animals like bees do, the Vikings could have used to give them true bearings. The Viking routes in the North Atlantic were often subject to dense fog and the stone could also be used to locate the sun on very cloudy days. The researchers said such sunstones could have helped the Vikings in their navigation from Norway to America before the discovery of the magnetic compass in Europe. They would have relied upon the sun's piercing rays reflected through a piece of the calcite. The trick is that light coming from 90 degrees opposite the sun will be polarised so even when the sun is below the horizon it is possible to tell where it is. They used the double refraction of calcite to pinpoint the sun by rotating the crystals until both sides of the double image are of equal intensity. Navigation was based on tables showing the position of the sun in the sky at various times of year, prior to the use of the compass by Europeans, around the 12th century. Added the researchers: "The Alderney discovery opens new possibilities as it looks very promising to find Iceland spars in other ancient shipwrecks, or in archaeological sites located on the seaside such as the Viking settlement with ship repair recently discovered in Ireland." The study is published in the journal Proceedings of the Royal Society A.
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