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Viking sailors roamed and ruled over the North Atlantic for three centuries beginning in the eighth century. A historical mystery is how they were able to navigate without a compass, in daylight and nighttime since the weather conditions were harsh and with cloudy periods of time lasting for days, their movement was greatly hindered and their orientation depended on the stars or the sun.
Legends speak of a strange “solar stone”, used by Vikings in the distant past, a device that acted as an ancestral GPS-like device.
In 1967 Danish archeologist Thorkild Ramskou launched a bold hypothesis: the Vikings used the polarization of light scattered by clouds using cordierite crystals in order to navigate. Only a few believed him because most people did not see how this theory was possible.
Almost half a century ago, a book called Waves, from a series of textbooks from the Berkeley Physics Course mentioned in an exercise the use of birefringence crystals as navigation instruments, something that would have allowed the Vikings to navigate and orient themselves even when the sun was obscured by clouds.
The Cern magazine, on the other hand, published an article where experts discuss a research done by Hungarian researchers. In the study, experts argued that the Vikings used Iceland spar, a clear variety of calcite common in Iceland and parts of Scandinavia. This incredible crystal has a very interesting property called birefringence: when light rays fall on calcite they will divide into two, forming a double image on its far side. Also, Iceland space is considered as a polarizing crystal, meaning that the two images would consequently have different brightness’s, all depending on the polarization of light. However, the study proposed had two setbacks. The first is there were no medieval books that speak about the possible use of solar stones in navigation, and the second is that this crystal can only be found in Iceland. This mineral is not found in Norway, Sweden, and Denmark.
However, Viking activity began about fifty years before the discovery of Iceland, which implies that the Vikings navigated across the Atlantic without Iceland spar during that time and that Iceland spar, therefore, may not be the crystal that the Vikings would have used to orient themselves while exploring the planet, if of course, they really oriented in themselves in a similar way.
In any case, the theory proposed by Thorkil Ramskou is more plausible since the Vikings could have used cordierite to orient themselves while navigating, and this mineral is found in Norway and Sweden, unlike Iceland spar.
Only in one occasion, medieval textbooks speak about the use of slarsteinn, as a device used as a pocket-sized ‘gadget’ that was used to determine the position of the sun, and, therefore, the time of day, no matter what the weather conditions were.
To add to the subject, a study published in the Proceedings of the Royal Society explains in details the ancient Viking navigation devices. The study, titled “A depolarizer as a possible precise sunstone for Viking navigation by polarized skylight”, written by, , , , and
Viking navigation from Norway to America in the northern latitudes remains a mystery for physicists, historians and archeologists. Polarimetric methods using absorbing dichroic crystals as polarizers to detect a hidden Sun direction using the polarized skylight have led to controversies. Indeed, these techniques may lack in sensitivity, especially when the degree of polarization is low. Here, we demonstrate theoretically and experimentally that using the transparent common Iceland spar as a depolarizer, the Vikings could have performed a precise navigation under different conditions. Indeed, when simply rotated, such a birefringent crystal can completely depolarize, at the so-called isotropy point, any partially polarized state of light, allowing us to guess the direction of the Sun.
By equalizing the intensities of the ordinary and extraordinary beams at the isotropy point, we show that the Sun direction can be determined easily, thanks to a simple sensitive differential two-image observation. A precision of a few degrees could be reached even under dark crepuscular conditions. The exciting recent discovery of such an Iceland spar in the Alderney Elizabethan ship that sank two centuries before the introduction of the polarization of light in optics may support the use of the calcite crystal for navigation purposes.
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Featured image credit: Vikings TV Series