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    Re: Viking sunstones in the Phil. Trans. R. Soc.
    From: John Huth
    Date: 2011 Feb 4, 02:37 -0500

    It's interesting that this chestnut keeps on giving.   The article mentions that they'd like to see a shipwreck with a sunstone on it.   In Leif Karlsen's book, Secrets of Viking Navigation, he mentions that a shipwreck in the 14th century was found with a calcite crystal on it - but as far as I can tell this hasn't gotten any other press.  Leif was an enthusiastic supporter of the idea.

    The authors suggest it could be used in fog.   I find that you can see some blue sky directly overhead if the fog isn't too dense, so that's plausible.  

    In any case, it makes for an interesting student project.

    On Fri, Feb 4, 2011 at 1:41 AM, Frank Reed <FrankReed@historicalatlas.com> wrote:

    At nature.com, there's a review of an article that's just been published in the Philosophical Transactions of the Royal Society on viking sunstones and polarization of light. The title of the review: "Did Vikings navigate by polarized light?" and subtitled: "'Sunstone' crystals may have helped seafarers to find the Sun on cloudy days."
    http://www.nature.com/news/2011/110131/full/news.2011.58.html

    This is old hat for most of us. While polarization of sunlight near sunrise or sunset does give a fairly good indication of the Sun's compass bearing at times when the Sun itself might be obscured by clouds, the practical value of this "trick" would be quite limited. Myself, I consider it essentially wishful thinking with no basis in actual history --at least so far. Thankfully, the nature.com article quotes two 'specialists' who make that very point. There's also a comment after the article suggesting that there are easier ways to detect polarized light, which is also true.

    -FER


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