Before Google Maps, GPS and compasses, Vikings used the sun to figure out where they were sailing.
A new report may have unlocked the key to understanding how the Vikings used the legendary sunstone to navigate the seas, even on overcast days.
Science Magazine notes that Norse sagas mention the sunstone and now, the report, "A depolarizer as a possible precise sunstone for Viking navigation by polarized skylight," claims that the devices could have been made out of calcite, which would have helped them to provide accurate readings in any weather.
The Guardian explains how this process might have worked:
Light is not polarized as it leaves the sun – in other words the electromagnetic waves vibrate in all directions perpendicular to the direction in which they are traveling. But as sunlight passes through the Earth's atmosphere, it is scattered and becomes polarized in a particular direction.
Vikings might have calibrated calcite crystal sunstones by scanning them across a clear sky and noting the sun's position when the crystal brightened. They could then repeat the trick to locate the sun when it was no longer visible.
Lead researcher Guy Ropars explained his team's thought process to Discovery News.
"Rather than thinking in term of polarizer, we have deliberately chosen to 'destroy' the polarization of the light," Ropars said. "Iceland spar behaves theoretically and experimentally like a perfect depolarizer."
To see how accurate calcite could be, the report authors built their own sunstone. Science Magazine reports that the team used a chunk of calcite from Iceland spar. The researchers found that their sunstone could predict the actual location of the sun with 99% accuracy.