November 2, 2011
Viking Sun Stone Not A Myth
Ancient Norse mariners used Icelandic rocks to help them navigate the ocean when the Sun and stars were obscured by clouds, according to a study published Wednesday in the Proceedings of the Royal Society A.
Over a thousand years ago Vikings ventured thousands of miles from their home toward Iceland and Greenland, and possibly even as far as North America, centuries before Columbus, by reading the position of the Sun and stars, and by way of landmarks, currents and waves.
Now experiments have shown that a mysterious crystal, known as the Icelandic spar, could detect the Sun accurately allowing seafarers to navigate the seas on cloudy days and nights. By holding the stone aloft, voyaging Vikings would have been able to find the Sun in the sky.
The new results show that Icelandic spars, which are formed from crystallized calcium carbonate, are good polarizers and could have been the raw material of mythical sunstones. The spars can be easily carved and formed into a rhombus shape necessary for light-fracturing, and a discovery of one on the wreck of an Elizabethan ship that sunk in 1592, could lay the foundation for researchers to confirm their theories.
Dr Guy Ropars of the University of Rennes, Brittany led an international team of researchers in finding the evidence to back up the claim that ancient mariners used light-fracturing crystals to find their way in the dense fog and clouds of the northern seas.
The team argues that Vikings used the Icelandic spar to fix the true bearing of the Sun to within a single degree of accuracy, even when the sun was below the horizon. This naturally occurring stone has the ability to “depolarize” light, filtering and fracturing it along different axes, the team explained.
Here´s how the crystal works: If you put a dot on top of the crystal and look through it from below, two dots will appear. “Then 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 explained to AFP in a telephone interview.
“A precision of a few degrees can be reached even under dark twilight conditions.... Vikings would have been able to determine with precision the direction of the hidden Sun,” he added.
The human eye, he added, has a fine-tuned capacity to distinguish between shades of contrast, and thus is able to see when the two spots are truly identical.
The findings bolster Viking legend of an enigmatic sunstone that, when held up to the sky, revealed the position of the Sun, even on the cloudiest and most intermittent of days. One Icelandic saga describes how King Olaf consulted Sigurd on the location of the Sun during cloudy, snowy weather.
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 polarization of the skylight, as many animals like bees do, the Vikings could have used Icelandic spar to give them true bearings.
Navigation was based largely on tables showing the position of the sun in the sky at various times throughout the year, prior to the use of the compass by Europeans, which was not invented until the 13th century.
But even in the era of the compass, crews might have kept such stones on hand as a backup, the study suggested.
“We have verified ... that even only one of the cannons excavated from the [Elizabethan] ship is able to perturb a magnetic compass orientation by 90 degrees,” the researchers wrote. “So, to avoid navigation errors when the Sun is hidden, the use of an optical compass could be crucial even at this epoch, more than four centuries after the Viking time.”
“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,” said the researchers.
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