In the 1960s, Danish archaeologist Thorkild Ramskou suggested that the Vikings used a sunstone to filter the sunlight so that it all had the same polarization, or direction. By rotating the crystal to and fro, the light would appear brighter or darker, depending on how the crystal was oriented. The brightest point would be toward the direction of the sun.
Two sunstone readings from different points in the sky would allow navigators to pinpoint the sun’s location. They could then hold up a torch in that direction to mimic the sun’s location, allowing its light to cast a shadow on the sundial.
Story: John Roach, MSNBC | Photo: Reuters