Vikings could have steered by polarized light

Feb 03, 2011 by Lin Edwards report
sunstone
Image: Donsimpson via Wikipedia.

(PhysOrg.com) -- The Vikings are said to have been able to navigate with the aid of "sunstones" that allowed them to see the sun on cloudy or foggy days. Now scientists in Hungary and Sweden say the sunstones could have been polarizing crystals.

The Vikings were the dominant seafaring explorers of much of Northern Europe and Britain from around 900 to 1200 AD. They were able to navigate their way around the thousands of kilometers of the north Atlantic with great skill and without the help of the , which was not then known in Europe. In the long days of summer at high latitudes they would also have had limited or no views of the stars to help them navigate.

Legend has it that these great Scandinavian used a "sólarsteinn," or sunstone, to help them, and stories mentioning the sunstone include the saga of King Olaf and Sigurd, the Icelandic hero. The king asked Sigurd where the invisible sun lay in the cloudy sky and then used a sunstone to check Sigurd’s answer.

Danish archaeologist Thorkild Ramskou suggested in 1967 that the sólarsteinn could have been a piece of Icelandic spar, which is calcite in the form of a transparent, polarizing crystal. These crystals are common in Iceland. Other candidates for sunstone include cordierite or tourmaline, both of which are common in Scandinavia.

A polarizing crystal allows only light polarized in one direction to pass through, and it appears dark or light depending on its orientation to the . Sunlight becomes polarized through the scattering of air molecules in the atmosphere, with the line of at a tangent to concentric circles with the sun at their center. Ramskou postulated that the Vikings could have rotated a polarizing crystal to check the direction of polarization and deduce the position of the sun when it was hidden by fog or was just beneath the horizon.

Scientists Gábor Horváth from the Eötvös University in Budapest, Susanne Ĺkesson from Lund University, and colleagues around Europe, have been investigating Ramskou’s hypothesis since 2005 because it had never been tested.

The researchers began by asking volunteers to identify the position of the sun in 180-degree fisheye lens photographs taken in northern Finland of the sky under twilight, foggy or cloudy conditions. They found the volunteers were inaccurate, making errors of up to 99 degrees.

This led Horváth and Ĺkesson to conclude the Vikings were unlikely to have relied on guesses using naked eye observations.

Then in 2005, the pair crossed the Arctic Ocean on the Oden, a Swedish icebreaker. During the trip they measured the polarization patterns of the sky under a wide range of weather conditions. They were surprised to learn that polarization patterns were very similar on clear and cloudy days, although the polarization was weaker in overcast conditions. This suggests the Vikings could have used this information if they had polarization crystals.

Horváth and Ĺkesson next plan to see if volunteers can use polarization crystals to determine the sun’s location in a range of weather conditions.

The and earlier seafarers used a number of navigational aids including using special sundials, the stars, migration paths of birds and whales, coastlines, distant clouds over islands, and so on. The sunstone could have been another important tool in their navigational aids kit.

The research paper is published in the Philosophical Transactions of the Royal Society B.

Explore further: Tooth buried in bone shows two prehistoric predators tangled across land, sea boundaries

More information: On the trail of Vikings with polarized skylight: experimental study of the atmospheric optical prerequisites allowing polarimetric navigation by Viking seafarers, Gabor Horvath et al., Phil. Trans. R. Soc. B 12 March 2011 vol. 366 no. 1565 772-782. doi:10.1098/rstb.2010.0194

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User comments : 13

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Moebius
1 / 5 (2) Feb 03, 2011
Seems possible, wouldn't it be easier to test the principle with a pair of RayBans first? Or a polarizing filter on a camera?
mvpgerman
1.1 / 5 (12) Feb 03, 2011
what a bogus claim,...i thought it is pretty much known by now,that the vikings are very brave but not very skilled seafarer !!!! they often got stranded in areas unknown to them because of lack of navigational support like the mentioned compass...they sometimes used ravens to find land behind the thick fog they just sailed into....that is also how they found greenland and later america,trough accident...so declaring them now ueber sailer is kinda silly...
PieRSquare
5 / 5 (2) Feb 03, 2011
Seems possible, wouldn't it be easier to test the principle with a pair of RayBans first? Or a polarizing filter on a camera?
There wouldn't be any point if you wanted know if the Vikings could have done it because they didn't have those things. The materials they're proposing are common so no real disadvantage to using them.
Moebius
1 / 5 (4) Feb 03, 2011
RayBans are polarized. If the hypothesis is correct you should be able to find the sun with them on when you can't with them off. If it doesn't work with a modern set of polarized lenses, it isn't going to work with crystals. Unless the mechanism is not polarized light in which case the RayBan test is also valid to prove that they had something else (if anything).
PieRSquare
4.3 / 5 (7) Feb 03, 2011
Again, the crystals are common so why bother using the RayBans? If the RayBans did work you'd just have to do another experiment to prove the Vikings could have done it because the crystals may not have the same performance characteristics.
xamien
5 / 5 (2) Feb 03, 2011
Both of you are correct in the ideas of it, however, your objections are fallacious. The use of polarized sunglasses would be enough to give it the Mythbuster stamp of "plausible", whereas the polarized crystals would be the real litmus test to determine the truth of the matter.
tigger
not rated yet Feb 03, 2011
Wow. Calcite is getting some coverage these days... first the paper clip cloaking device and now this.
Moebius
1 / 5 (4) Feb 03, 2011
Again, the crystals are common so why bother using the RayBans? If the RayBans did work you'd just have to do another experiment to prove the Vikings could have done it because the crystals may not have the same performance characteristics.


Are you sure the crystals are polarized? Is the sample crystal well polarized? Is it as polarized as what the vikings may have used? Is it even the same crystal as the vikings used? You can't be sure of the answer to any of those questions but you can test the hypothesis absolutely with modern polarized lenses. Use some common sense before you post.
antialias
5 / 5 (4) Feb 04, 2011
And precisely for that reason testing it with modern polarized lesnes will only tell you that it works with modern polarized lenses.

The only telling result would be if it didn't work with modern polarized lenses. But anyways ist does since ants use polarized light to navigate:
(w)(w)(w).imls.uzh.ch/static/CMS_publications/wehner/literatur/pdf07/90.pdf
PieRSquare
3 / 5 (3) Feb 04, 2011
could have been a piece of Icelandic spar, which is calcite in the form of a transparent, polarizing crystal. These crystals are common in Iceland. Other candidates for sunstone include cordierite or tourmaline, both of which are common in Scandinavia.

Yet again, common materials. Go nuts, take a whole bag of inexpensive crystals with you. If they weren't known to polarize they obviously wouldn't have come up. This would be able to answer if they COULD have done it with materials that were available. They only way you could answer if they DID do it would be to find archeological evidence. The RayBan question could be answered casually without a need for a study. "Common sense" says that no-one would be interested in funding or publishing the RayBan version (except maybe RayBan).
sculptor
not rated yet Feb 04, 2011
I'd read years ago that Iolite or "water saphire" was used for this purpose.
Moebius
2 / 5 (4) Feb 05, 2011
Pretty clueless about the scientific method aren't we PieR? Glad you aren't doing research.

The hypothesis has 2 parts. That polarized light can be used to find the sun on a cloudy day and that natural stones can be used as polarized filters. You test them separately first, then together.
scidog
not rated yet Feb 07, 2011
well lets all get a hunk of this stone from the local rock shop, try it out and re-post the results.as Spring breaks we are getting foggy weather in the Midwest.this should be as easy as a 7th grade science fair project..go too it..