March 7, 2013
Sunstone Found In British Shipwreck Confirms Ancient Viking Navigation
Lawrence LeBlond for redOrbit.com - Your Universe Online
In the series premiere of the History Channel´s new saga ℠Vikings,´ we find the main character, Ragnar Longbrok, demonstrating how a sunstone can help him navigate. This mysterious, often deemed magical, crystal has purportedly also been able to help actual ancient Viking sea goers find their way for centuries, even on the cloudiest of days.
Researchers from France say they have discovered from a shipwreck a crystal very similar to a sunstone — a crystal that could have been used to help the Vikings navigate their way across the expansive ocean long before the invention of the magnetic compass. It is believed that Vikings discovered North America hundreds of years before Columbus did in 1492.
The team, from the University of Rennes, said they found the crystal while examining the wreck of a British ship (discovered 30 years ago), which sank off the island of Alderney in the English Channel in 1592. The oblong crystal is the size of a pack of cigarettes and was found located next to a pair of dividers — suggesting it was part of the navigational equipment.
After careful examination, it was determined that the crystal was in fact that of Iceland spar — a type of calcite known for diffracting light into two separate rays. The team said this spar could detect the sun to within a degree of accuracy — allowing the ancient mariners to navigate under cloudy conditions.
Dr. Guy Ropars, lead researcher on the discovery, and his colleagues said the crystal could pinpoint the sun to within a few degrees even when it was below the horizon.
The team tested a similar crystal to that of the Iceland spar and demonstrated that by rotation it was possible to find the point at which the two beams of light converge, which indicate the direction of the sun. Their experiment worked both in cloud cover and when the Sun has set.
How could the Vikings have determined where the sun was once it had set?
Perhaps the best answer is that light coming from 90 degrees opposite the sun will be polarized. When the sun sets below the horizon, this 90 degree polarization can still be reflected through diffraction, allowing navigators to accurately pinpoint the Sun´s location.
But why did the British ship, which sank hundreds of years after the invention of the compass, still use a sunstone for navigation?
The Iceland spar found on the British ship definitely came long after the reign of the Vikings in the ninth and 10th centuries. But scientists surmise that the use of sunstones persisted as a back-up to the often unreliable early magnetic compasses, which were first introduced to Europe in the 13th century. Beyond that, there are only sketchy references in old Viking legends on the use of the sunstone.
Perhaps the best known use of sunstones comes from the Icelandic saga of King Olaf, who consulted with Sigurd on the location of the Sun during cloudy, snowy weather. To confirm Sigurd´s response, 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."
Polarization is not just something the Vikings and other early mariners may have relied upon. Many animals, including pigeons, bees and fruit flies, rely to some extent on polarization for navigation.
Before the invention of the compass, navigation was based on tables showing the position of the sun in the sky at various times throughout the year. It is possible that the sunstone could have also played a huge role in Vikings finding their way to North America, as the North Atlantic Ocean is often plagued by fog and cloud cover, sometimes for days on end.
"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 researchers concluded, as reported by The Telegraph.
The study findings are published in the latest issue of the Proceedings of the Royal Society A.