Monday May 28, 2018 Q&A

How did the Vikings navigate their ships while sailing?


1 By studying the strength and direction of waves.

2 By looking into a crystal

3 By relying on the captains’ amazing sense of direction

Correct answer: 2, they looked into a crystal.

With the wind in their sails, Viking ships boldly sailed across the North Sea and beyond. The brave and brawny Vikings – if we are to believe the cliché – were on a quest to conquer new, faraway lands. Some experts believe that Vikings first landed in North America some 500 years before Christopher Columbus and centuries before the compass reached Europe. So how did they do it, given that the sun in Scandinavia can shine for 20 hours a day in the summer (making navigation by the stars impossible) and the weather is often cloudy? It turns out their secret may have been a special type of crystal with extraordinary physical – rather than mystical – properties.

Stories from the Viking era sometimes mention a “sunstone.” But it wasn’t until the 1960s that a scientist familiar with the unique properties of a crystal called Iceland spar made the connection. Iceland spar is fairly common in Scandinavia and has the distinctive feature of dividing light that passes through it into two rays. One ray is usually brighter than the other, but if the crystal is aligned perfectly with the light source, then both rays shine just as brightly. That means Vikings could have used Iceland spar stones to determine the exact position of the sun. And this mechanism works even when it’s cloudy.

To test this theory, in 2011 French researchers developed a computer program in which algorithms play the role of Viking ships. They used their program to simulate thousands of boat trips between Norway and Greenland, playing with three key variables: cloud cover, the type of mineral used as a “sunstone,” and the number of times a day the algorithm checked its direction against the sunstone. The scientists found that if the sunstone was checked every three hours, the ship had a 92–100% chance of reaching its destination. But if it was checked only once every four hours, the success rate fell to 32–59%. And checking it less often meant the ship would get lost at sea.

This study indicates that the hypothesis made in the 1960s is probably right. No Iceland spar stones have been found on Viking ships, but one was found among the navigation equipment of an old English ship. Apparently the Vikings still have more to teach us.

Article in Proceedings of the Royal Society: