Blinded by the Viking Sunstones

Alun Science, The Past 6 Comments , , ,

So, there’s these sun­stones that some people think Vik­ings could have used to nav­ig­ate to Amer­ica. It’s pos­sible though the evid­ence is weak.

A Vik­ing Ship. Not the one you might expect, but wait and see. Photo by Eoghan O’Lionnain

A few months back there was a paper where the phys­ics was sound but the his­tor­ical con­text was lack­ing. Today the news is a new paper, A depol­ar­izer as a pos­sible pre­cise sun­stone for Vik­ing nav­ig­a­tion by polar­ized sky­light. My prob­lem with the earlier paper was that while the phys­ics made sense, there was no real attempt at his­tor­ical con­text. This paper is different.

The test crys­tal from Ropars et al. 2011.

The Alder­ney Stone, from Ropars et al. 2011.

A depol­ar­izer as a pos­sible pre­cise sun­stone for Vik­ing nav­ig­a­tion by polar­ized sky­light is not a paper about Vik­ing nav­ig­a­tion at all. It’s about tests on a sun­stone found on an Eliza­bethan ship by Alder­ney. Update 15 Nov 2001. It’s about tests on a piece of Icelandic spar that the authors have used as a sub­sti­tute for the Alder­ney stone. The paper doesn’t describe the meth­ods used to ensure the sub­sti­tute was a good proxy for the ori­ginal. I’ve included the images of the ori­ginal and the test stone. I can see some super­fi­cial dif­fer­ences and more dis­cus­sion of how the test stone was pre­pared could have been help­ful. The phys­ics is lovely and makes sense, but this paper on Tudor nav­ig­a­tion doesn’t cite any research on Tudor navigation.

The argu­ment is this:

  1. If you place some­thing with a small hole in front of the Alder­ney sun­stone two areas of light appear.
  2. By get­ting the areas to the same bright­ness you can work out where the sun is.
  3. That might have been use­ful in Eliza­bethan times because can­nons can deflect mag­netic compasses.
  4. But we’ve not checked any his­tor­ical records to see how Tudor sail­ors coped with that, nor if our made-up hole thing has any his­tor­ical evid­ence for it
  5. Because sun­stones means Vik­ings! VIKINGS I TELL YOU!

Now, if you’re inter­ested in the optics of cal­cite, this is a good paper — but why would you be inter­ested in the optics of cal­cite? The only obvi­ous reason I can think of is his­tor­ical. And a paper that tackles a his­tor­ical prob­lem by pretty much ignor­ing the his­tor­ical period your arte­fact comes from seems to me to be eccentric.

Any­way, if you were sail­ing in north­ern lat­it­udes and you couldn’t see the sun due to mist, but the light was bright enough for polar­isa­tion to be detect­able, then you could use this device to loc­ate the dir­ec­tion of the sun. The sun­stones would have to be bet­ter polar­isers than the fil­ters I use for my cam­era, because I can’t detect any notice­able polar­isa­tion in the over­cast sky today. Once you have a dir­ec­tion, with no time or alti­tude for the obser­va­tion, what are you going to do with that?

The cov­er­age I’ve seen at the Guard­ian and at the BBC, is cred­ited to two good sci­ence journ­al­ists, yet neither has con­tac­ted a Tudor or Vik­ing his­tor­ian for their opin­ion. This baffles me.

Update 3rd Nov 2011: Wired / Sci­en­ceNow do report that no sun­stone has been found with a Vik­ing ship­wreck or set­tle­ment. They also have an inde­pend­ent expert com­ment­ing on the pos­sib­il­it­ies of Tudor nav­ig­a­tion. Unfor­tu­nately it’s a bio­lo­gist on the dif­fi­culty of sight­ing from a Vik­ing ship.

Is there some­thing clever about the paper I’ve overlooked?

Photo: Vik­ing Line by Eoghan O’Lionnain. Licenced under a Cre­at­ive Com­mons BY-SA licence.

6 Comments

  1. Thony Christie

    Thank you for being a voice of reason in a sea of bullshit.

    Reply

  2. judith weingarten

    Like you said the first time round, “just because it could have happened doesn’t mean it did.” I keep try­ing to per­suade some engin­eer­ing friends that, while the Alex­an­drian Greeks inven­ted a steam engine device, they didn’t use it for min­ing or other indus­trial applic­a­tions. They simply don’t believe me.

    Reply

  3. Erich Jacoby-Hawkins

    The use of a stone to find the sun is doc­u­mented in the sagas — three examples are lis­ted here: http://www.nordskip.com/vsagas.html

    There is already plenty of evid­ence that the Vik­ings (or more prop­erly, Norse sea­farers) ten­ded to sail along lines of lat­it­ude, which required them being able to meas­ure lat­it­ude to stay on course. The could do this at night off the Pole Star, and dur­ing the day by sight­ing off the sun at peak height (noon). On an over­cast day, they would need the sun­stone to loc­ate the sun. And they would determ­ine noon simply by whenever the sun was highest over the horizon.

    Basic­ally, min­eral and optical sci­ence has finally found a set of min­er­als that had the prop­er­ties required, and were sourced in Norse areas.

    Reply

  4. Alun

    It’s a sens­ible com­ment Erich. I can see the argu­ment about whether such a stone phys­ic­ally exists, but Hor­vath et al. have done this at the start of the year and it’s been done many times before that. Hor­vath et al. did at least make ref­er­ence to the sagas in their paper, which doesn’t hap­pen in this one. In fact you’ve made a much more com­pre­hens­ive his­tor­ical argu­ment for sun­stones in your com­ment. Given they had a whole paper which was ostens­ibly about nav­ig­a­tional prac­tice in the past (Vik­ing nav­ig­a­tion is the first keyword) I think that’s a problem.

    It’s doubly wor­ry­ing because there is noth­ing Vik­ing in the paper. Nor is there any real dis­cus­sion of any his­tor­ical con­text. They make no case why a Tudor arte­fact is con­nec­ted to Vik­ing navigation.

    For com­par­ison, if I presen­ted evid­ence that Wal­ter Raleigh vis­ited North Amer­ica, would that be evid­ence for Vik­ings get­ting there earlier? In a way it shows the ocean was cross­able, but I can’t see any his­tor­ian tak­ing that ser­i­ously. What con­vinced his­tor­i­ans that Norse set­tlers had got to the new world was find­ing the L’Anse aux Mead­ows site.

    I’ve read through the paper again this morn­ing and found I made an error read­ing it. I thought the tests were done on the Alder­ney stone. In fact they were done on a new crys­tal. The valid­ity of the optical tests depends on how close the mod­ern pre­par­a­tion is to the his­tor­ical arte­fact, so I’ll add a cor­rec­tion after post­ing this comment.

    Reply

  5. judith weingarten

    More of the same? http://www.archaeology.org/1203/trenches/vikings_iceland_spar_crystal_navigation.html

    Reply

  6. Alun

    That’s a good spot. Yes, it’s the same paper. It gets pub­lished in dead tree form on the 8th of March 2012.

    Reply

Leave a Reply

*