(Note that calcite has long been known to exhbit polarization effects, and polarized plastics are used in some sunglasses.)
Very interesting. I can see the sunlight's polarization being sensed by the calcite so that in the right direction, equal polarization of the light on on each side of the sun might be detectable in those grooves to show the sun's direction even through an overcast or even (stretching it a little) with the sun under the horizon.
I wonder how seasonal tilting of the earth might affect this possible effect. But I suspect it could indicate north better than a magnetic compass. There were probably some area in the Viking's sojourns where North would be straight down -- and magnetic north drifts around quite a bit anyhow.
Great video. Too bad I don't have my polarized sunglasses any more to explore that polarization possibility.
As a side note, I am always skeptical when someone claims that a device or technique wasn't known or in use "back then."
Terry, 230RN
