The Vikings were notorious across Europe during the Iron Age, from the late 8th century CE to 1066 CE. Along with their reputation as fearsome warriors and unforgiving raiders, they were also great explorers of the sea – thought to have reached Iceland, Greenland, and even as far as North America and the Middle East.
A few decades ago, it was unclear how they navigated these misty and unknown seas, until researchers found some mysterious sunstones in a ship wreckage. Now, Hungarian researchers have been playing around with these mysterious stones to shed light on how they were used to find new lands. Their findings have been published in Proceedings of the Royal Society A.
A sunstone is a flat tile of crystallized calcium carbonate, known as Iceland spar. If you are in a region of extremely low light because of thick fog or a snowstorm, you hold it up to the sky and let the light going through it polarize and scatter through a process of double refraction. It does this even when the Sun is obscured by weather conditions.
The sailor would then have to find two celestial points in the scattered light of the sunstone. By moving the sunstone in front of their eyes and noticing the changing intensity of the light, they could determine the direction the sunlight was coming from. They then used that information to form an estimated position of the obscured Sun and combined it with information from a Viking sun-compass, a kind of specialized sundial, so they could determine which direction was North.
“The theory of sky-polarimetric Viking navigation has been widely accepted for decades without any information about the accuracy of this method,” the study authors wrote. They brought this theory to the lab to see if and how it actually helped these bearded Iron Age explorers.
They gathered 10 participants and asked them to try to find the position of the Sun in a digital planetarium after a brief run through of how it all works. More than 2,400 attempts later, they found that nearly half (48 percent) of the tests were more accurate than not using a sunstone. In particular, the most accurate instances were when the Sun was closely to the horizon.
This led the researchers to conclude that the sunstone was a tool used during the early hours of sunrise or during sunset, especially when the Sun was obscured by fog or snow. Also, since the sunstone worked best at these times, they even suggest that the Vikings could have actively set sail and navigated during the morning or evening.