The Vikings were great sailors and great navigators - of this there is no doubt. But despite their evident skills, their ability to travel significant distances out of sight of land gave rise to speculation as to whether they had access to some form of navigation aid (Not a magnetic compasses as they would not have been available or not until very late Viking period). 40 years ago a Danish archaeologist suggested that they might have used crystals (known as sunstones) to polarize sunlight and thus find the Sun’s location. This. website lists some of the pros and cons of this idea
Interestingly today’s Guardian carried a report that seems to give additional weight to the sunstone idea Tests aboard a research vessel in the Arctic ocean found that certain crystals can be used to reveal the position of the sun even if the sky was obscured by cloud or fog.
Researchers led by Gabor Horvath at Eotvos University in Budapest spent a month recording the polarisation of sunlight while at sea. Although polarisation is not apparent to the naked eye, it can be seen using certain crystals which could work in all but the worst weather conditions
Professor Michael Berry, a physicist at Bristol University, said: "They've shown that even if the sky is full of clouds and moisture, the polarisation of the sunlight doesn't change very much, and that's a real surprise. If you know the time already, then once you know the position of the sun you know what direction you're sailing in."
Another one of those sort of news items that fascinates me…