Physicists from Eötvös Loránd University in Hungary have determined that the sunstones claimed to be used by Vikings to navigate on foggy and cloudy days could provide accurate results. Vikings living between 900 and 1200AD did not have magnetic compasses, and their ability to navigate was attributed in part to the use of calcite, cordierite or tourmaline crystals which functioned as linear polarizers to help them determine geographic north. The crystals can split sunlight into two beams, and when the crystal is turned, splitting the two beams at the same brightness, a navigator could see the polarized rings around the...