Scientists have found that a Viking sunstone may have indeed been helpful when it came to navigating the seas under sunless or starless skies.
The Viking king Ragnar demonstrates the use of a sunstone in navigation, as portrayed in the television show Vikings. [Still from the History Channel]
We know a significant amount of information about the Vikings and their exploits. We know that they raided several places around Europe from the 790s to 1066, the year the Normans finally conquered England. However, the Vikings also managed to sail to lands beyond Europe. There's evidence that they reached North Africa and the Middle East, and perhaps North America as well. Thus, researchers have been wondering for decades how the Vikings managed to navigate long, unknown distances, given that the sun and stars won't always be visible for the entire duration of the journey.
Historians thought it possible that the Vikings used a tool called a sunstone in order to navigate when the sun or stars weren't visible. A sunstone is a mineral made of refractive birefringent material.
How did the Vikings navigate the seas under a cloudy sky?
Icelandic legends and archaeological evidence attest that Vikings may have used sunstone for navigation, but it hasn't been clear how. This 2016 study explores how the Vikings were able to navigate unknown waters with just a refractive, polarizing piece of rock.
Researchers at Eötvös Loránd University in Hungary analyzed a few types of birefringent minerals in different kinds of weather in order to evaluate how useful the minerals were in navigation. The researchers believe that the use of Viking sunstone entailed a three-step process. First, the navigator would hold the stone up to the sky and determine where the light is coming from. Second, this information would help the navigator figure out where the sun itself is. Third, the navigator would use tool called a shadow stick to determine which direction is north.
The researchers previously tested the accuracy of the first two steps, and the sunstone passed. Testing the third step was thus the priority. 10 volunteers were asked to determine the position of the sun as they stood in a digital planetarium. Instead of a sunstone, however, the volunteers used dots to “navigate”. The researchers conducted a series of 2,400 trials to test the efficacy of sunstone in navigation.
Icelandic spar, which may have been the stone that the Vikings used [Photo by ArniEin/Wikipedia/CC BY-SA 3.0]
According to the results of the trials, the volunteers had 48% success in producing accurate readings. The researchers revisited their findings in a more recent study and found the conditions in which the sunstones were ideal to use, as well as the degrees of uncertainty that using the sunstone would produce.
Apparently, if the Vikings did use sunstone to navigate, it would have been the most useful when the sun was low in the sky, and when the time was close to the summer solstice. They would have had the best results in the early to mid-morning, when it was foggy or cloudy, around the third week of June.
This, however, isn't conclusive evidence of the use of Viking sunstone in navigation. It's possible that we may never be completely sure that the Vikings did indeed use sunstone to find their way around unfamiliar seas. However, this is evidence that using sunstone in navigation can indeed be effective.
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