Mythical Viking Sunstones Could Have Worked

Physicists from Eötvös Loránd University in Hungary have determined that the sunstones claimed to be used by Vikings to navigate on foggy and cloudy days could provide accurate results. 

Vikings living between 900 and 1200AD did not have magnetic compasses, and their ability to navigate was attributed in part to the use of calcite, cordierite or tourmaline crystals which functioned as linear polarizers to help them determine geographic north. The crystals can split sunlight into two beams, and when the crystal is turned, splitting the two beams at the same brightness, a navigator could see the polarized rings around the sun, effectively showing its placement in the sky.

The scientists tested the method by computer simulation by following the sailing routes of 1,000 Viking voyages starting from Hernam (nowadays the Norwegian Bergen) along the 60°21′55″ N latitude, which was the main sailing route of the Vikings to their settlement Hvarf in south Greenland. From Bergen to Greenland, the Viking sailors had to accurately keep the western direction parallel to the 60°21′55″ N latitude. 

The study, published in the journal Royal Society Open Science, states that sunstones are surprisingly successful even under cloudy conditions - achieving success rates of between 92.2 and 100 percent during spring equinox and summer solstice if a navigator checked the sailing direction every three hours.

There were some limitations to the simulations which didn't, for example, account for strong winds or storms, so navigation success may be slightly over-estimated. If the Vikings headed too far south during the three-week voyage, they would not have reached Greenland and would have either perished in the Atlantic Ocean or reached Canada at a time earlier than Columbus, say the researchers. There is archaeological evidence of Viking settlements along the western coastline of Newfoundland, Canada. 

Earlier research, also conducted by a team including the Hungarian researchers, indicates that Vikings may also have been able to navigate after sunset. This could have been achieved by using a sun-compass, a modified sundial, with sunstones to create a "twilight board." The researchers examined a fragment of an 11th-century dial found in Uunartoq, Greenland, and attempted to extrapolate its features into something that would allow Viking navigators to detect the position of the sun from the twilight glow on the horizon passing through two sunstones. If the technique was employed, it could have allowed navigation well after sunset, since the twilight glow can last all night at high latitudes in summer.

"Developing a twilight board is surely not beyond the capabilities of seafaring people," said researcher  Balázs Bernáth. "Sunstones are mentioned in written sources and they could be used during civil twilight, although it is not trivial how one can accurately estimate the position of the sun with them."