You might think seafaring Vikings–who traveled hundreds of miles on rough seas between 750 and 1050 AD–would be adrift on cloudy days: not only did they lack compasses, but they were often traveling so far north that the sun never set, and thus couldn’t use stars to navigate. But scientists are finding new evidence to support the existence of what was once considered a mythical navigational tool: the sólarsteinn, or sunstone.
It all starts with an Icelandic legend about a man named Sigurd. As Nature News reports:
The 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.” In 1967, Thorkild Ramskou, a Danish archaeologist, suggested that this stone could have been a polarizing crystal such as Icelandic spar, a transparent form of calcite, which is common in Scandinavia.
Knowing that our atmosphere can scatter sunlight and polarize it, Gábor Horváth, an optics scientist at Eötvös University in Budapest, and Susanne Åkesson, a migration ecologist from Lund University, Sweden decided to put calcite to the test.
First they tested human abilities. Using photographs of cloudy skies, they tested how well subjects could estimate the sun’s position, and found that, with errors of up to 99°, the unaided eye isn’t the best navigational device. So in 2005 they they traveled the Arctic Ocean measuring the sky’s polarization patterns, and their findings were nothing less than eye-opening. From Nature News:
The researchers published their findings in the journal Philosophical Transactions of the Royal Society B.The researchers were surprised to find that in foggy or totally overcast conditions the pattern of light polarization was similar to that of clear skies. The polarization was not as strong, but Åkesson believes that it could still have provided Viking navigators with useful information…. “I tried such a crystal on a rainy overcast day in Sweden,” she says. “The light pattern varied depending on the orientation of the stone.”
Even though archeologists have yet to find a sunstone in a Viking wreck, which would put all debate over sunstone use to rest, this research still goes a long way in resurrecting what was once considered mere myth. And the coast looks very clear indeed as the scientists gear up for their next study: to test whether volunteers can accurately determine the position of the sun using these clear calcite crystals.
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