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Re: [MedievalSawdust] Digest Number 2782

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  • Broom
    ... I think previously guessed would be more accurate; nothing is proven about this, and it s unlikely anything ever will be, unless we found some Iceland
    Message 1 of 1 , Nov 4, 2011
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      Geirfold:
      > Nothing like doing a study on something that was proven 40 years ago.  I have several books on Viking Age history that were printed in the 60's and 70's that already gave that information.

      I think "previously guessed" would be more accurate; nothing is proven
      about this, and it's unlikely anything ever will be, unless we found
      some Iceland spar in a boat. As another commenter pointed out, there
      are other polarizing stones like Iolite; any of them could have done
      the job. But even the polarizing-crystal method is merely guesswork;
      the references might have been to (placebo) magic, or something we
      haven't thought of.

      As an optical engineer, one of the most counter-intuitive things I've
      ever learned is that the sky's brightness doesn't vary with compass
      direction - even when the sun is visible. The only exception is that
      of course it's brighter where the sun actually /is/, and under hazy
      conditions, in its general area. But if you take a light reading *of
      the sky alone*, with no land visible (and no individual clouds), it
      doesn't vary N-E-S-W. (It does vary with elevation angle.)

      This is part of why it's so easy to get lost hiking. If you're in a
      forest, or it's hazy overhead (which blends shadows), the sun
      direction is fairly unknowable.

      However, the polarization of light /does/ vary with angle, and as the
      article notes, it is mostly polarized 90-deg away from the sun. So, if
      you can polarize your view (by being a bird, insect, or
      crystal-peering Norse sailor), you can still determine the sun, and
      thus the vague compass direction.

      ' | Broom IAmBroom @ gmail . com
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