Viking Sunstones

In the northern seas, Viking navigation took place in few favourable conditions as weather or high latitudes often rendered the sight of the Sun or stars impossible, which were used like landmarks. By 1967, a Danish archeologist put forth a theory according to which Viking ships' helmsmen might have used so-called 'sunstones' to remedy that. A rocky crystal, or a 'sunstone' or a 'Viking compass,' allowed the sailors to spot where the Sun was lying when it was not visible. Such theories became very fashionable with the Viking navigational deeds, when one recalled, by the 1960's, that they would had discovered North America about 1000 A.D. That theorecist also based upon ancient Icelandic sagas and too about the use which was made at the time of a so-called 'twilight compass' by Scandinavian airline pilots, which worked upon the polarization of light. In the Hrafns Saga, for example, you can read: 'the weather was thick and stormy [...] The king looked about and saw no blue sky [...] then the king took the sunstone and held it up, and then he saw where [the Sun] beamed from the stone.' Candidate-minerals like that sunstone are miscellaneous semi-precious gemstones like Icelandic calcite, or Norwegian iolite and cordierite. Tourmaline and andalusite might also fit. Such sunstones in any case surely had some value, or a some use given that they are mentioned in the sagas. Researchers of the University of Rennes in France managed to re-build one from a calcite crystal along with its instructions of use. Once cleaved the crystal is affixed with a screen bearing a small hole to limit the field of view; the whole is turned into the direction of the center of the sky illuminated by the hidden Sun as sunlight, when crossing the stone, is dividing into two beams of light. The user then rotated the sunstone until both beams aligned themselves and reached a same -and maximal- brightness. That gave the direction of where the Sun was lying. Such a result works upon the fact that the polarizing sunstone acts like a polarizing filter and the effect yielded when the filter is paralleled to the polarization plane of the light of the Sun. Cordierite crystal is found under the form of pebbles along the coast of Norway; once cleaved, it changes its color -from blue to yellow- and brightness when rotated before a polarized light, like, for example, the one of the Sun as damped by clouds or the horizon. Of note too is that Iceland later was the main production site of optical calcite, a material which allowed the discovery and study of polarization. The 2.8-inch wide Uunartoq disc, a supposed Viking compass as found in Greenland in 1948 in an 11th-century convent, was featuring a central domed object, more easily casting a shadow of the Sun, and likely used in conjunction with sunstones and a wooden slab. That would have constituted a 'twilight compass' with a accuracy of 4 degrees. Such a compass likely could work up to 50 minutes after sunset around the equinox

Some however argued that Vikings mostly roamed the seas in summer and that they then could relatively easily determine the position of Sun, even when some clouds were present, without any artefact and that, at last, when the sky was completely overcast, any sunstone could not be used at all. Sagas moreover do not really hint to any detailed direction of use of Viking compasses nor was any sunstone even found like a archeological evidence (or that is controversial). The only such archeological proof of such a sunstone comes much more later, in a Elizabethan shipwreck dated 1592 in the English Channel. They could not use a magnetic compass as a powerful cannon was aboard the metal of which would have interfered with! At last and foremost, opponents of the theory of the sunstone often value that Viking navigational techniques as corroborated by sagas and archelogoy had been constructed, with time or even errors of some sailors, upon coastal navigation and the observation of varied natural phenomenons. Vikings excelled at using coastal landmarks as seen from the sea as they had become trained to observe sea currents, the journey of animals (like fish banks, migrating birds, seals, etc.), or weather events. Northern birds migration routes thus could hint to the Vikings that those were really heading somewhere as, when following the route, they could eventually find lands. That likely was the case, for example, to discover Iceland from the Feroe islands. Like a conclusion, it looks plausible that Viking sunstones be used by Viking sailors as they were part of a vaster set of navigational techniques