This posting has no real local connection, but I find it fascinating to read about how the Vikings might have navigated correctly even on cloudy days – using sunstones.
The idea is that ancient mariners looked up through these sunstones on overcast days, when the entire sky looked equally bright. Light making its way through a cloudy sky is often polarized — if the way the crystal was angled matched the polarization of this light, the sky would look brighter, but if not, it would look darker. By rotating the sunstones to and fro, the sky would thus appear to periodically brighten and fade. Then, by looking for the patch of sky that was brightest regardless of the clouds, Vikings could have identified where the sun was and then have used the sundial to figure out which direction was north. CSM
Some literary references to sunstones support this hypothesis. Now testing is underway to see if it would have been possible. Cool or what?