Sunstone satnav: How Vikings used mysterious crystal to guide them to America

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Sunstone satnav: How Vikings used mysterious crystal to guide them to America

    Norse warriors located sun through clouds with Iceland spar crystal

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By Simon Tomlinson

Last updated at 12:44 PM on 2nd November 2011

Ancient legends of Viking mariners using mysterious sunstones to reveal the position of the sun on a cloudy day may well be true, according to a new study.

Before the invention of the compass, Norse adventurers travelled thousands of kilometres across the oceans toward Greenland and most likely as far as North America centuries ahead of Christopher Columbus.

Evidence shows that these fearless seamen navigated by reading the position of the sun and stars along with an intimate knowledge of landmarks, currents and waves.
Inventive: A new study claims to have revealed how the Vikings were able to navigate on cloudy days with a sunstone

Inventive: A new study claims to have revealed how the Vikings were able to navigate on cloudy days with a sunstone

But how they could voyage such distances across seas at northern latitudes while hampered by light obscuring clouds and fog remained a mystery.

While experts have long argued that Vikings knew how to use blocks of light-fracturing crystal to locate the sun through dense clouds, archeologists have never found solid proof.

Doubts also remained as to exactly what kind of material it might be.

An international team of researchers led by Guy Ropars of the University of Rennes in Brittany, says they have the answer.
Ancient-day sat nav: The refractive properties of calcite crystal - otherwise known as Iceland spar - were used to pinpoint the sun through clouds

Ancient-day sat nav: The refractive properties of calcite crystal - otherwise known as Iceland spar - were used to pinpoint the sun through clouds

HOW VIKINGS USED THE ICELAND SPAR CRYSTAL

According to the new study, the Vikings would have relied upon the sun's piercing rays being reflected through a piece of the calcite crystal.

Researchers found that if you put a dot on top of the crystal and look through it from below, two dots will appear due to the double refraction of the Iceland spar.

Using this, they could pinpoint the sun by rotating the crystal until both sides of the double image are of equal intensity.

At that angle, the upward-facing surface indicates the direction of the sun, according to the scientists led by Dr Guy Ropars.

A precision of a few degrees can be reached even under dark twilight conditions, so the Vikings would have been able to determine with precision the direction of the hidden Sun.

The human eye, he added, has a fine-tuned capacity to distinguish between shades of contrast, and thus is able to see when the two spots are truly identical.

Vikings, they argue, used transparent calcite crystal - also known as Iceland spar - to fix the true bearing of the Sun to within a single degree of accuracy.

The naturally occurring stone has the capacity to 'depolarise' light, filtering and fracturing it along different axes, the researchers explained.

The recent discovery of an Iceland spar aboard an Elizabethan ship sunk in 1592 - tested by the researchers - bolsters the theory that ancient mariners were aware of the crystal's potential as an aid to navigation.

Even in the era of the compass, crews might have kept such stone on hand as a backup, the study speculates.

'We have verified that even only one of the cannons excavated from the ship is able to perturb a magnetic compass orientation by 90 degrees,' the researchers wrote.

'So, to avoid navigation errors when the Sun is hidden, the use of an optical compass could be crucial even at this epoch, more than four centuries after the Viking time.'

The study appeared in Proceedings of the Royal Society A: Mathematical and Physical Sciences, a peer-reviewed journal published by Britain's de facto academy of science, the Royal Society.

http://www.dailymail.co.uk/sciencetech/ ... erica.html