Many centuries ago 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.
One Icelandic saga describes how, during nasty 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”.
So, plenty of ancient tales speak of Norse mariners using mysterious sunstones to navigate the ocean when clouds covered the Sun and stars. According to a recent research, these tales can be true to life.
Experts have long argued that Vikings knew how to use blocks of light-fracturing crystal to locate the Sun when it was cloudy, archaeologists have never found proof, so it were some doubts, considering the nature of the stone.
An international team of researchers under the direction of Guy Ropars of the University of Rennes in Brittany, basing on experimental and theoretical evidence, says they know the answer.
They suppose that Vikings used transparent calcite crystal, called Iceland spar, to fix the true bearing of the Sun. Experiments have shown that a crystal 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.
“The Vikings could have discovered this, simply by choosing a transparent crystal and looking through it through a small hole in a screen,” Guy Ropars said. “The understanding of the complete mechanism and the knowledge of the polarization of light is not necessary.”
How does it work? 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,” Ropars explained.
“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.”
Even nowadays, when different types of compasses are invented, crews may keep such stone on hand as a backup, said researcher.
“We have verified … that even only one of the cannons excavated from the ship is able to perturb a magnetic compass orientation by 90 degrees. 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 study was published in Proceedings of the Royal Society A: Mathematical and Physical Sciences, a peer-reviewed journal published by Britain’s de facto academy of science, the Royal Society.
Experts said, “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.” [Via The Telegraph (UK) and Physorg]