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Re: Zonnesteen - Sunstone - Solarstein.
From: John Huth
Date: 2013 May 16, 15:42 +0200

The first discussion of sunstones was advanced by Thorkild Ramskou in an article called "Solstenen," in a Danish journal, Skalk from 1967. He was the first to raise this point, to the best of my knowledge.

He advanced the idea based on text in a Norse saga talking about a sunstone, and was aware that there is a large quantity of calcite in Iceland (appropriately called Iceland spar). Calcite is birefringent, so it is sensitive to the polarization state of the blue sky. In principle, if the sun is shrouded in fog, but you can see some blue sky overhead, you could use this to find the direction to the sun by looking at the polarization state of the sky. (birefringent = it splits the two polarization states into two)

A lot has been written about the possible use of sunstones since Thorkild's original article. I have had students who tested it. It definitely can be used to determine the polarization state of the sky. A minor warning is that the optical axis is 6 degrees off of the actual crystal axis.

One recent major proponent of sunstones was a guy named Leif Karlsen, who tested calcite extensively. Leif was also the first person, to my knowledge, who advanced the idea that this particular artifact (in that article) was used for navigation.

Having said all of that - was it really used by the Norse for navigation? One doesn't know. The calcite mine in eastern Iceland opened up in the latter half of the 17th century and was mined for optical instruments during the industrial revolution.

What would help the case for sunstones as a real navigational device would be an archaeological find that had more context favoring its use - e.g. in a Norse shipwreck closer to the period of its being mentioned in the saga that Thorkild referenced.

I personally have used calcite to determine the polarization state of the sky and attest that it works. Again, I think that stronger archaeological evidence would be required to establish that it was used. It would also be interesting if some new saga was uncovered that also mentioned it. As it is, the segment Thorkild references says that it was used when the sky was cloudy - which isn't a condition when you could use blue-sky polarization. I don't necessarily dismiss the passage based on that, as it is conceivable that the writer knew of a sunstone, but didn't really know how it was employed.

On Thu, May 16, 2013 at 11:47 AM, Guus Dekker <guusdekker@telenet.be> wrote:

In March I read an article in a Dutch newspaper (NRC, March 7 2013) about "Sunstones". The article tells for the first time in history they find a Sunstone on the plotting desk from a ship wreck from 1592. A sunstone is a vintage navigation device 5x3 cm (1x2 inch), a crystal named "Iceland Calsietcrystal". They say that the Vikings did use it for centuries ago (1000 - 1300 ac). This material makes it possible to SEE polarized light by refraction in the atmosphere, forming circles around the sun. This crystal doubled the rings. If the rings are equally strong in intensity, then it point stait to the sun, EVEN when the sun is blocked by heavy clouds or just set. Polarized light has s one direction vibration frequency like a polarized sunglass, so only a single frequency is passed. Researchers describe the Sunstone in "The Proceeding of the Royal Society A". Did someone hear or know something about this "Sunstone" device ?! Guus Dekker, Belgium. ---------------------------------------------------------------- NavList message boards and member settings: www.fer3.com/NavList Members may optionally receive posts by email. To cancel email delivery, send a message to NoMail[at]fer3.com ----------------------------------------------------------------
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