Long before the magnetic compass found its way from China to Europe, the Vikings sailed the North Atlantic, populating Iceland and, from the end of the tenth century, Greenland and Newfoundland. This is confirmed by numerous archaeological finds. However, how the Northmen and women succeeded in reaching their distant destinations unerringly in the unpredictable Arctic waters between Europe and North America has not yet been fully clarified.
The fact is that the Vikings mainly navigated the seas using a so-called sun compass, an instrument similar to the sundial, consisting of a wooden disc with a short rod in the center. At night, the stars may have also served as a mean of navigation. But how did the Vikings manage to orient themselves when the oceans became foggy or when dense clouds covered the sun?
After all, such adverse weather conditions in the far north represent the rule rather than the exception. In some Scandinavian legends, including the “Saga of King Olaf”, mysterious “sun stones” are mentioned for such cases, which would have allowed the sailors to navigate the treacherous seas all the way to the West even if the sun was not out.
Although there is no archaeological evidence for the use of such crystals in Viking seafaring, several studies have made their use as a navigation aid seem quite plausible in recent years. This assumption is corroborated by a stone that scientists had discovered in navigational instruments found in the wreck of a 16th-century British sailing ship.
Polarized light Experiments with this birefringent calcite, also known as the Icelandic spar, showed that it is possible to determine the position of the sun very precisely even with a cloudy sky thanks to polarized daylight. The crystal must be held up and rotated slowly. If the light polarized by the clouds gives rise to two beams of equal brightness, one will point in the direction of the sun.
The minerals cordierite and tourmaline gave similarly good results in the experiments. So far the evidence is that the stones do work as it was described in the old stories. But Could the vikings really find their way to the Americas — thousands of miles away — by using polarimetric navigation based on the sunstones? Definitely, according to physicists Dénes Száz and Gábor Horváth from the Eötvös Loránd University in Budapest.
With the help of experiments and extensive computer models, the scientists were able to prove that this form of navigation could even have been extremely precise. Száz and Horváth, who have been studying the Sunstone for years, conducted a total of more than 36,000 simulations, in which they sent virtual Viking ship types from Norway to South Greenland in twelve different weather scenarios. They assumed that more than 1,000 years ago, the Norsemen sailed westwards at about the 60th parallel and more or less parallel to it, and took about three weeks to cross at an average speed of eleven kilometers per hour.
As departure dates, they chose the spring equinox, as this probably marked the beginning of the nautical season, as well as the summer solstice, the longest day of the year. Taking into account previous experiments, the simulations provided astonishingly accurate navigation results. According to the researchers in the journal Royal Society Open Science, a Viking ship navigating using a sunstone would have reached South Greenland in 92 to 100 percent of all cases, even in thick clouds provided the navigator had determined the sun’s position every three hours. At four-hour intervals, the ships would have run off course quickly and target accuracy would have dropped to 32 to 59 percent.
“Thus, our results clearly show that polarimetric navigation using calcite, cordierite or tourmaline may have been surprisingly successful even in a heavily clouded sky, if the course has been regularly monitored,” says Horváth.