Vikings may have used polarizing crystals to navigate

Nature : A Viking legend tells of a glowing “sunstone” that, when held up to the sky, revealed the position of the Sun even on a cloudy day, writes Jo Marchant for Nature. It sounds like magic, but scientists measuring the properties of light in the sky say that polarizing crystalswhich function in the same way as the mythical sunstonecould have helped ancient sailors to cross the northern Atlantic. A review of their evidence is published today in Philosophical Transactions of the Royal Society B.