For a long time, scientists could not understand how the Vikings traveled from Scandinavia by sea, overcoming thousands of nautical miles. It is known that they were excellent navigators and in the 9-11th centuries sailed to Russia and Ireland, and in the 10th century they discovered Greenland. However, how did they navigate, overcoming such long distances, if the compass was discovered only in the 16th century?
Sagas and legends speak of "sun stones" that were used for navigation even in bad weather - the stones helped them find the sun in the sky, even if it was completely covered by clouds. In particular, this is mentioned in the saga of the settlement of Greenland from the biography of King Olaf, who ruled Norway in the late 900s. Interestingly, in 1948 a copy of the Uunartoka disk was found, which, in combination with the same sun stone (Solstenen), could serve for navigation. According to scientists, the device was a sundial with marks-cardinal points and carvings, indicating a change in shadow.
The first to suggest that such stones really existed was an archaeologist from Denmark Torvild Ramsku. In 1969, he stated that it could be a natural crystal that polarizes light (for example, calcite). In the process of observing cloudy areas of the sky, rotating the crystal, it was possible to find those areas from where, due to Rayleigh scattering, fully polarized light emanates. By drawing perpendiculars to the line that connects these areas, you can find the sun hidden behind the clouds, knowing its exact position.
Archaeologist Gabor Horvat and his colleagues have done computer simulations of the Viking voyages from Bergen in Norway to Hwarf on the southern coast of Greenland, a voyage that took about three weeks. The model took into account 1000 such trips and the use of calcite (as well as cordierite, tourmaline and aquamarine) for navigation - an error was indicated for each stone. The journey began at the summer solstice or vernal equinox, the cloudiness was set by chance. The model showed a very high probability of success for this method of navigation - 92%. However, this indicator was true only if the stone was checked every 3 hours - when the course was corrected every 4 hours, the probability of success dropped to 32–58%, for verification every 6 hours - to 10%. Scientists have suggested that it was an error in navigation that led tothat the Vikings landed on the shores of Newfoundland in North America (the territory of modern Canada) in 985-1000. Later they founded the Vinland settlement there. One way or another, the Vikings discovered North America and explored its territory long before the voyages of Christopher Columbus.
Although the theory that calcite was the very "sun stone" has not been proven (it was not found either in their graves or in the places where settlements were located), this assumption well explains the navigational abilities of the ancient navigators. Moreover, calcite was found among the tools on a British ship that sank in 1592, and there is also evidence of pilots using polarizing stones in the 20th century, when the compass could malfunction.