How the Vikings navigated to strange lands with unerring accuracy has puzzled researchers for centuries. Now their secret has been revealed and the answer is as surprising as it is illuminating: mysterious crystals the Vikings called "sunstones."
Few things in history capture the imagination, boldness and courage of the history of Mankind as the exciting tales of the adventurous—and often fearless—Vikings. Much is known about their culture, traditions and expeditions, but how they navigated the northern latitudes where the sun is often obscured by thick clouds and ice fogs remained an enduring mystery.
Although some experts on Norse technology and navigation argued for many years that the Vikings most likely used light refracting crystals, no proof was found that supported the hypothesis and other academics voiced strong skepticism about the likelihood.
Archaeologists never came across any evidence that proved the Vikings used such materials to assist navigation.
And for forty years, there the matter lay.
But now a new study, published in the peer-reviewed Proceedings of the Royal Society A: Mathematical and Physical Sciences, claims the solution has been found: Icelandic crystal spars.
Guy Ropars of the University of Rennes in Brittany led an international team intent on finding the crystals they were certain the Vikings must have used. The researchers found their answer lay in the light refracting properties of calcite crystal, also called Iceland spar. Using such crystals, the Vikings were able to locate the sun even through fog or heavy cloud cover.
Depolarization allowed Vikings to easily navigate southern Polar waters
The secret to the navigational properties of an Iceland spar is using the crystal correctly to determine the exact position of the sun.
The Vikings were able to so effectively use the properties of the crystal to find the position of the obscured sun that their navigation would often be correct within a degree. Taking their bearings regularly would enable them to make minor course corrections keeping them on the heading they desired and maintaining their course.
For the crystal to polarize light, it had to be cut into a rhombus shape. The research team showed that the sunstones can be cleaved and shaped into that shape relatively without much effort.
To effectively use the depolarizing crystals, the team discovered that by placing a mark, or dot, on the apex of the crystal and then looking through the spar from the bottom towards the sky, the refractive properties would heighten the area where the sun was hidden to the naked eye.
Once the general area was known, by simply twisting the crystal while pointed at the sky, the double images of the two dots produced by the refraction of sunlight through the clouds would reach an equal intensity—and pinpoint the location of the sun.
This physical phenomenon of doubly refracted light is known as birefringence, the "splitting of a light wave into two different components—an ordinary and an extraordinary ray." [Source]
The study reports that even during periods of dark twilight, the Iceland spars still work their refractive magic. The key to the crystal being its unique refractive qualities that also depolarized and fractured a light source into two images.
This "mysterious crystal" permitted the Vikings to navigate by the sun even when it was unseen and easily make voyages to their colonies in Greenland and Iceland. It also assisted their discoveries of new lands including North America.
Use of crystals continued for centuries
Because early compasses were sometimes unreliable for navigation, sea-goers may have continued using the Icelandic spars as a back-up navigational system. This theory gained some credibility recently when an calcite crystal was discovered inside a 16th Century British sailing vessel.
The sunken ship lends credence to the argument that the sunstones were used by navigators as long as four centuries after the Vikings.
Since some Vikings emigrated to England, it's logical they would have brought their sailing technology with them.
"Sunstone satnav: How Vikings used mysterious crystal to guide them to America," Daily Mail