Blinded by the Viking Sunstones

So, there’s these sunstones that some people think Vikings could have used to navigate to America. It’s possible though the evidence is weak.

A few months back there was a paper where the physics was sound but the historical context was lacking. Today the news is a new paper, A depolarizer as a possible precise sunstone for Viking navigation by polarized skylight. My problem with the earlier paper was that while the physics made sense, there was no real attempt at historical context. This paper is different.

A depolarizer as a possible precise sunstone for Viking navigation by polarized skylight is not a paper about Viking navigation at all. It’s about tests on a sunstone found on an Elizabethan ship by Alderney. The physics is lovely and makes sense, but this paper on Tudor navigation doesn’t cite any research on Tudor navigation.

The argument is this:

1. If you place something with a small hole in front of the Alderney sunstone two areas of light appear.
2. By getting the areas to the same brightness you can work out where the sun is.
3. That might have been useful in Elizabethan times because cannons can deflect magnetic compasses.
4. But we’ve not checked any historical records to see how Tudor sailors coped with that, nor if our made-up hole thing has any historical evidence for it
5. Because sunstones means Vikings! VIKINGS I TELL YOU!

Now, if you’re interested in the optics of calcite, this is a good paper – but why would you be interested in the optics of calcite? The only obvious reason I can think of is historical. And a paper that tackles a historical problem by pretty much ignoring the historical period your artefact comes from seems to me to be eccentric.

Anyway, if you were sailing in northern latitudes and you couldn’t see the sun due to mist, but the light was bright enough for polarisation to be detectable, then you could use this device to locate the direction of the sun. The sunstones would have to be better polarisers than the filters I use for my camera, because I can’t detect any noticeable polarisation in the overcast sky today. Once you have a direction, with no time or altitude for the observation, what are you going to do with that?

The coverage I’ve seen at the Guardian and at the BBC, is credited to two good science journalists, yet neither has contacted a Tudor or Viking historian for their opinion. This baffles me.

Update 3rd Nov 2011: Wired / ScienceNow do report that no sunstone has been found with a Viking shipwreck or settlement. They also have an independent expert commenting on the possibilities of Tudor navigation. Unfortunately it’s a biologist on the difficulty of sighting from a Viking ship.

Is there something clever about the paper I’ve overlooked?

Photo: Viking Line by Eoghan O’Lionnain. Licenced under a Creative Commons BY-SA licence.