8/25/2016 Sunstones give most accurate readings when sun is low in the sky | Daily Mail Online http://www.dailymail.co.uk/sciencetech/article-3709258/Did-Vikings-rely-sunset-sunrise-navigate-Sunstones-accurate-readings-… 1/21 Home News U.S. Sport TV&Showbiz Australia Femail Health Science Money Video Travel Fashion Finder Latest Headlines Science Pictures Login shares 251 NAVIGATING WITH SUNSTONES Dr Gábor Horváth and his team have Did Vikings rely upon sunset and sunrise to navigate? Sunstones give most accurate readings when sun is low in the sky Vikings are thought to have used sunstones navigate in cloudy skies Researchers have tested whether it is possible to use these to navigate They found two calcite crystals can be used to determine the sun's position They also found the method was more accurate close to sunrise or sunset By RICHARD GRAY FOR MAILONLINE PUBLISHED: 23:01 GMT, 26 July 2016 | UPDATED: 23:33 GMT, 26 July 2016 They were feared warriors who terrorised much of northern Europe and beyond through the Iron Age. But carried by their longboats, the Vikings also circumnavigated across vast stretches of open ocean, travelling as far as the Middle East and even North America. Now researchers have shed new light on how they may have achieved this feat – with the help of the sunrise and sunset. The Vikings are thought to have navigated across the vast Atlantic Ocean and the North Sea with the help of sunstones (crystal of Iceland spar pictured) that allowed them to work out the position of the sun even when it was cloudy or foggy. New research has suggested this technique was most accurate at sunset or sunrise Scientists have studied the techniques the Viking sailors may have used to help them pick their way from Scandinavia to far lung places. Historians have long suspected the Vikings used sun-compasses to orientate themselves while at sea. 33 View comments +4 Site Web Enter your search Download our iPhone app Download our Android app Today's headlines Most Read Did someone lose a shoe on Mars? Oddly shaped rock sparks more bonkers alien theories China unveils its Mars rover concept: Images provide the first glimpse of the vehicle that will launch in... The world's largest pyramid is hidden inside a mountain in Mexico: Early settlers built a church on top of... Beware the CYCLOPS beetles: Scientists create threeeyed insects to understand how new traits evolve Now that's a time bomb! 700yearold hand grenade used in the Crusades is found off the coast of Israel Sitting in a traffic jam really IS bad for you: Motorists breathe in 40% more deadly pollutants when sat at... WhatsApp will now share your phone number with Facebook: Policy change paves the way for more targeted ads Never run out of data again: Google launches 'WiFi Assistant' on all Nexus phones Uber will now let Londoners book journeys WEEKS in advance in another blow to the taxi industry Does Free range chicken really taste better? Knowing how an animal was raised can trick our taste buds Why this picture should put you off sweet treats for life: Every item is 19 YEARS OLD but look like the day... The Kremlin's hidden past: Remains of buildings, graves and people the Soviets tried to destroy are... Does YOUR iPhone 6 have 'Touch Disease'? A design defect is rendering devices useless and Apple can't fix... Selfdriving taxis are here! Startup beats Google and Uber to debut autonomous rides in Singapore How classy are YOU? The 50 things that will reveal how well brought up you were (including shopping at... MORE HEADLINES DON'T MISS 'No one should feel like they're not good enough': Furious Stacey Solomon defends her bikini body after she was slammed by body shamers All aboard the love boat! Jade Jagger goes topless as she packs on the PDA with husband Adrian Fillary in Spain Things were hotting up out at sea Jemma Lucy ATTACKS Holly Rickwood after she enjoys date with her ex David Hawley in explosive Ex On The Beach catfight Pretty in pink! Braless Jessica Alba puts on a smoking hot display in a vibrant maxi dress as Thursday, Aug 25th 2016 5PM 25°C 8PM 19°C 5Day Forecast
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8/25/2016 Sunstones give most accurate readings when sun is low in the sky | Daily Mail Online
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NAVIGATING WITHSUNSTONESDr Gábor Horváth and his team have
Did Vikings rely upon sunset andsunrise to navigate? Sunstones givemost accurate readings when sun islow in the sky
Vikings are thought to have used sunstones navigate in cloudy skiesResearchers have tested whether it is possible to use these to navigateThey found two calcite crystals can be used to determine the sun's positionThey also found the method was more accurate close to sunrise or sunset
By RICHARD GRAY FOR MAILONLINEPUBLISHED: 23:01 GMT, 26 July 2016 | UPDATED: 23:33 GMT, 26 July 2016
They were feared warriors who terrorised much of northern Europe and beyondthrough the Iron Age.
But carried by their longboats, the Vikings also circumnavigated across vaststretches of open ocean, travelling as far as the Middle East and even North America.
Now researchers have shed new light on how they may have achieved this feat – withthe help of the sunrise and sunset.
The Vikings are thought to have navigated across the vast Atlantic Ocean and the North Seawith the help of sunstones (crystal of Iceland spar pictured) that allowed them to work out theposition of the sun even when it was cloudy or foggy. New research has suggested thistechnique was most accurate at sunset or sunrise
Scientists have studied the techniques the Viking sailors may have used to help thempick their way from Scandinavia to far �lung places.
Historians have long suspected theVikings used sun-compasses to orientatethemselves while at sea.
33View comments
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suggested the Vikings navigated usingthree hypothesised steps aftercalibrating the sunstone:
Calibration step: In cloudless weather,the navigator watched the sky througha sunstone while rotating it to and fro infront of his eyes. This allowed them todetect periodic changes in the intensityof transmitted skylight. He had torotate the crystal until its well-determined orientation ( eg minimal ormaximal intensity of skylighttransmitted through a dichroicsunstone, or minimal or maximalintensity difference between the twoslots/spots of a birefringent sunstone),where it was �ixed, and thereafter hecalibrated the crystal by engraving thedirection pointing towards the sun onthe crystal surface.
Navigation step 1: Applying thissunstone rotational adjustment under acloudy or foggy sky at two differentcelestial points, the navigator coulddetermine the directions perpendicularto the local E-vectors of skylight shownby the engraved straight markings ofthe sunstones, pointing towards thesun.
Navigation step 2: The intersection ofthe two celestial great circles crossingthe sunstones parallel to theirengravings gives the position of theinvisible sun.
Navigation step 3: Using the Vikingsun-compass, the navigator couldderive a true compass (e.g. North)direction from the estimated positionof the invisible sun.
* source Royal Society Open Science
In cloudy or foggy weather, they alsomay have used crystals known assunstones to help pick out the sun.
Now, in a series of studies published bythe Royal Society, a team of physicists atEötvös University in Budapest, Hungary,have tested whether this is possible.
They found that the Viking navigatorswould have needed to follow three stepsto ensure they could keep their vesselspointed in the right direction.
First they would have determined thedirection the light from the sky wasbeing polarised using two sunstones.
They could then use this to determinethe direction of the sunlight andcalculate its elevation.
They could then use a 'shadow stick' tocast the appropriate shadow on the suncompase to work out where North was.
In two studies published earlier this year,the researchers showed that the �irst twosteps were possible depending on thetype of crystal used for the sunstone.
They found that in overcast conditionscalcite gave the most accurate readingwhile cordierite and tourmaline weremore error prone.
But in a new experiment, published inthe Proceedings of the Royal Society A,the research team have shown that whilethe Vikings could have estimated theposition and elevation of the sun withsunstone, they would have been best todo it when the sun was lowest in the sky.
This means that if the Vikings tookreadings shortly after sunrise and beforesunset, they are most likely to havestayed on the correct course.
Dr Gábor Horváth, an expert in environmental optics at Eötvös University who led theresearch, said: 'The theory of sky-polarimetric Viking navigation with sunstones iswidely accepted.
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HOW DO SUNSTONES WORK?Sunstones detect the 'polarisation' ofsunlight - the way rays of light arescattered in different planes when theyreach the atmosphere.
The stones act as a �ilter, similar to the�ilters used in polarised sunglasses.
Light can only shine through the crystalif it is polarised in a particular direction.All other types of light are blocked.
The Vikings made long journeys at sea often in conditions that meant they could not see thesun (recreation of Viking longboat pictured). The sagas mention the use of mysterioussunstones and historians believe these could have been crystals found on the beaches ofNorway and Iceland
The popular TV series Vikings (pictured) depicts how the Vikings may have used sunstones tonavigate
'According to our �indings, the ideal periods for sky-polarimetric Viking navigationare immediately after sunrise and before sunset, because the North errors are thelowest at low solar elevations.'
There are few clues as to how the Vikings navigated across the oceans in thearchaeological record.
A fragment of a wooden dial, dating tothe ninth century, found in the ruins of aconvent in Greenland is thought to bepart of a sun-compass.
With such a device the Vikings wouldhave been able to �ind the direction ofnorth, and so work out their ownheading, with high precision, but only inclear weather.
Some experts have suggested that theVikings used special crystals calledsunstones that polarise the light to help
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The amount of polarised light in anyparticular direction depends on theposition of the sun in the sky at thetime.
Experienced navigators would quicklybe able to work out the location of thesun by turning the stone around.
them �ind the sun when it was coveredby clouds or fog.
Sunstones are described in some of theViking sagas but there is little physicalevidence of what these were.
Several potential crystals such as calcite,tourmaline and cordierite can be foundon the beaches of Norway and Icelandwhere the Vikings are known to have lived.
However, the theory that the Vikings used sunstones has been controversial.
In a study published in January this year, Dr Horváth and his team showed that itwas possible to use these stones to work out the direction of light was coming from.
There is little hard evidence of how the Vikings navigated across the ocean (painting of Vikinglongboat pictured) but the new research suggests it may have been possible using sunstones
This is because the light passing through the crystals was polarised, meaning as itwas rotated it would allow different amounts of light through depending on itsorientation.
When the amount of light passing through was at its brightest, it means it is alignedwith the polarisation of light in the atmosphere.
Markings on the crystal surface, made by calibrating the stone in clear conditions,could reveal where the direction of the light was coming from.
Dr Horváth and his team found using two sun stones and drawing two large circlesparallel to these engravings it was possible to work out the position of the invisiblesun.
In their latest paper the researchers examined whether it was then possible toestimate the elevation of the sun and so project an imaginary sunray onto thesurface of the sun compass by adjusting the shadow stick to the appropriate height.
They claim this estimation of solar elevation was probaably performed usingmeasures of �ists and �ingers.
FINDING EVIDENCE OF SUNSTONES UNDER THE SEA In 2002, a dive to the wreck revealed, among many artefacts, the mysterious lumpof crystal that is now the focus of international scrutiny.
As nobody knew quite what it was, it was put in a safe place and little notice wastaken of it until Professor Albert Le Floch, head of the research team, spotted areference to it on the website run by volunteers of the Alderney Maritime Trust.
He was further intrigued to discover that, in 2006, a set of brass dividers used formap-reading were also found in the wreck, just 3ft from where the crystal had beenfound.
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This encouraged the idea that it had been part of the navigational equipment.
Following a visit by Professor Le Floch to the island last year, a small specimen wastaken from the rock.
And, as the research paper is about to reveal, it has been con�irmed as Icelandicspar — which, although common around Alderney, has never been found in blockslike this one, about the size and shape of a cigarette packet.
This implies it was indeed with the stricken ship when it went down.
Using 10 male parti�icpanets, the researchers asked them to estimate the position ofthe sun in a digital planetarium using black dots to represent the spot determinedusing the sunstones.
They found that in 2,400 tests, 48 per cent of them were more accurate than onedegree.
They found that the most accurate estimations was when the sun was close to thehorizon.
This, they claim, suggests the Vikings probably navigated immediately after sunriseand before sunset to ensure their headings were as accurate as possible.
Writing in the paper, the researchers said: 'In reality a Viking navigator had toperform such an estimation with regard to an actually unseen sun.
'The latter is obviously a more di�icult task. Thus, the elevation errors presented inthis work underestimate the real errors of the third step of sky-polarimeric Vikingnavigation.
'On the other hand, Viking navigators were surely more experienced in theestimation of elevation angles than our test persons.'
EVIDENCE OF SUNSTONES IN ANCIENT ICELANDIC LEGENDS An Icelandic legend about the travels of the Norwegian king Olaf in the 11th centuryrefers to sunstones.
One winter's day, Olaf met a farmer's son named Sigurour, who boasted that hecould sense the position of the sun even in a snowy sky.
The story describes how the assembled company looked out of the window but'could nowhere see a clear sky'. After asking Sigurour to tell him where the sun was,the king ordered his minions to fetch 'the solar stone' to test the young man'sclaims.
'He held it up and saw where light radiated from the stone and thus directly veri�iedSigurour's prediction.'
Read more:rspa.royalsociet...Adjustment errors of sunstones in the first step of skypolarimetric Viking navigation: studies with dichroiccordierite/ tourmaline and birefringent calcite crystals | Open Science
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