Ancient mariners, including Vikings, well-oriented in the sea by the stars and the Sun. But the legend says that brave Scandinavian warriors were able to obtain a lot of information even from the sky covered with clouds.

Medieval sources claim that they used a mysterious "sun stone", also known as the "Viking compass".
Various medieval sources mention the mysterious "sun stone", also known as the "Viking compass" as a navigational tool for sailors. They say, they determined the position of the Sun (and hence parts of the world even if it was hidden by the cloud haze or mist.

In 1967 Danish archaeologist Thorkild Ramskou put forward an explanation of these legends. He suggested that the ancient texts it was about transparent minerals polarizing light passing through them. Recall that polarization, if simplistically, this is the direction of propagation of light wave. Because the light from the sky too polarized in accordance with the Rayleigh model, sailors could look up through the stone, slowly turning it in different directions.

The matching and mismatching of the plane of polarization of the light scattered by the atmosphere and the crystal was expressed in the form of a darkening and enlightenment of the sky as the reversal of the stone and the observer. A number of such serial "measurements" would help with some decent accuracy to know where the Sun.

Experts nominated several candidates for the role of solar stone - Icelandic spar (transparent version of calcite), and tourmaline and ijolite. What mineral is used Vikings - hard to say, all these stones were available to them.

It is curious, that in the twentieth century, ijolite got in aviation as a polarizing filter in the instrument, intended for determining the position after sunset. In fact, and in the twilight glow of the sky is polarized, and because the exact direction of hiding the light you can easily find out, having a "Polaroid" vision. The reception will work even if the Sun had dropped to seven degrees below the horizon, that is, through tens minutes after sunset. This fact, by the way, is well aware of the bees, but to him we will return.
In General terms, the principle of the Viking compass was clear long ago, but the big question was experimental verification of the idea. Experiments and calculations in this direction last few years devoted researcher Gabor Horvath from the University of Otvos in Budapest.

In particular, together with colleagues from Spain, Sweden, Germany, Finland and Switzerland, he studied painting of polarized light under a cloudy sky (and archaeologists from time to time find sunken in the mist) in Tunisia, the Viking ships and modern enthusiasts Hungary, Finland and build them up, but still not all the secrets of the sailors of the past are revealed.

Scientists have summarized the results of the experiments. In short: the original figure of polarization in the sky still find even under the clouds, although he is very weak, and it makes a noise itself cloudiness (or misty shroud). In both situations, the coincidence of the picture polarization with perfect was the best, the thinner the cover of clouds or fog, and the more it breaks, supplying even a fraction of direct sunlight.
Gabor and his associates have also modeled navigation when completely covered with a veil cloudy sky. It turned out that in this case "fingerprint" polarization continues and, theoretically, it is possible to calculate the position of the Sun. But the degree of polarization of the light was very low. In practice, this means that the armed not with polarimeters, and solar stones Vikings could hardly notice the weak fluctuations in the brightness of the sky, looking through the crystal. Navigation under thick cloud cover, if it was possible, was not accurate, - concluded scientists.
However, the investigation undertaken by the Croat, has shown, that the legend of solar stone and explanation of his Thorkild - credible and scientifically based.