NavList:

"That sounds like the Viking Sun Stone."

What you should say is "this sounds like the regrettable, un-historical legend which has been fashioned in recent decades around the story of the 'Viking Sun Stone' ". There is zero evidence that Vikings used sky polarization for navigation.

But sky polarization is real and definitely useful for navigation in some specialty applications. High Arctic navigation is one of those specialty applications. If you have never seen sky polarization, you owe it to yourself to do some real-world experiments. And all you is a pair of polarizing sunglasses! You might also find that you have a polarizing filter on an old sextant. 

The light from the clear blue sky is partially polarized. The band of strongest polarization is centered about 90° away from the Sun in the sky. When the Sun is low, or below the horizon in twilight, that band of polarization stretches across the sky passing nearly through the local zenith on a band that is perpendicular to the Sun's azimuth. If you can observe that polarization band, and observationally it is certainly easy to get the azimuth of the band within 5°, then you also have the observed azimuth of the Sun (+/-180°, but that ambiguity is never a problem). If you also have enough computation ability, you can figure out the actual azimuth of the Sun. And thus you get a rather good compass from a clear blue sky. Try it!!

I used to include this in some of my introductory celestial navigation workshops but haven't in a few years. More recently, before stargazing cruises that I host, while we're waiting to board close to sunset, I sometimes entertain folks by asking them to point their sunglasses straight up and turn left and right. It's an "ooh, ahh" moment...

Frank Reed