Back in the day, if you were going Viking (the jurys still out on whether thats technically a verb, but we'll go with it) then being able to sail your ship in a straight line was a pretty big advantage. Navigating using a sundial was childs play to any sailor worth his salt, but thats not all that helpful in the low-light conditions of the North Atlantic, with its cloudy skies, short days and long shadows. Vikings ability to navigate their way across vast swathes of open ocean and perhaps even to the Americas, come rain, shine or sunset, was uncanny. Whilst everyone else was sailing around in circles, Vikings could pretty much guarantee that they would end up exactly where they wanted to be, without bashing into any rogue continents along the way (looking at you, Columbus). A clue as to how they did it could be found in the medieval references to a magic crystal or Sunstone that allowed Vikings to navigate. Scientists were puzzled as to what it could possibly be until, in 2013, such a crystal was discovered in an Elizabethan shipwreck. It is now believed that the Vikings were able to harness the crystals properties of double refraction to cast distinct light and shadow on their sundial compasses and calculate the suns position, even when it was nowhere to be seen. Turns out they were much more than a bunch of pillaging barbarians after all.
