> 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.
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