A recently discovered hunk of mineral may be an example of the legendary Viking "sunstone" that Norse seaman used to help them navigate the open ocean. Scientists from the University of Rennes in Brittany have been studying the piece of crystal, found in the debris field of a late 16th century Elizabethan English shipwreck off the Channel Islands in the English Channel.
The seafaring abilities of the Vikings were remarkable. In small vessels they sailed the North Sea, the Baltic, the Mediterranean and, of course, the North Atlantic. The Viking settlement at L'Anse aux Meadows at the northern tip of Newfoundland is generally accepted proof that Viking sailors reached North America centuries before Columbus.
The Vikings accomplished these passages without the help of sextants or chronometers or almanacs. The tools they used included latitude hooks for determining latitude as well as dead reckoning and their experienced seamans' eye for observing the clues around them such as marine life, birds and water color. The reports of a tool called a sunstone, however, were held by some to be a myth, not an actual real navigation tool. The sunstone reportedly possessed a crystalline structure that allowed its users to determined the bearing of the sun. When combined with latitude readings from a latitude hook, the sunstone acts as a sun compass and allows for setting east/west courses even when the sky was overcast.
According to some legends, there was another way that Vikings suspected that land lay to the west of their Scandinavian homeland: when atmospheric conditions are right, light rays can be ducted long distances. These rare conditions have been suggested as a way that ducted images of distant land were seen by Viking observers, giving them another reason to explore to the west.