The sun was not necessary for Vikings to navigate, say researchers Vikings may have used a special crystal called a sunstone to help navigate the seas even when the sun was obscured by fog or cloud, a study has suggested. Researchers from Hungary ran a test with sunstones in the Arctic ocean, and found that the crystals can reveal the sun's position even in bad weather. This would have allowed the Vikings to navigate successfully, they say. The sunstone theory has been around for 40 years, but some academics have treated it with extreme scepticism. Researcher Gabor Horvath from...