NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Viking sun compass artifact and Viking sun stones.
From: Geoffrey Kolbe
Date: 2009 Jun 07, 07:06 +0100
From: Geoffrey Kolbe
Date: 2009 Jun 07, 07:06 +0100
There was an interesting program on the TV back in 1999 when a reconstruction of a Viking trading ship was sailed out of Roskilde (I think) to somewhere via an island in the Shetlands where it was deemed quicker to drag the ship over a narrow isthmus rather than go around the island. (It wasn't!) I can't remember the details, but it was a deep sea journey of some days and they had Robin Knox-Johnston along as navigator. He made up a little sun compass along the lines of the one that had been excavated in Greenland in 1947 (another was discovered in Poland in 2000 it seems). It seemed to work quite well. A day or so before the journey, Robin Knox-Johnston calibrated the device by scribing a line along which the tip of the short gnomon's shadow tracked across the base-plate during the day. The implication was that it was a use once and throw away sort of device, which would possibly explain why the Viking original was rather crude and why we have not found more of them. Of course, the device works only when direct sunlight is available and as I recall, Robin Knox-Johnston's other navigating skills were required to keep the boat on course. I see Robin Knox-Johnston has a piece on his website about this voyage. See http://www.robinknox-johnston.co.uk/da/20090 I have used a sun compass of a different sort in the Sahara desert. See www.pisces-press.com/C-Nav/images/sun_compass.jpg For this, the time of day is required and the device is rotated for the sun's azimuth at that time of day. It was a small device, but good to a couple of degrees none-the-less and certainly good enough to keep a dead-reckoning track of our car. The Viking 'sun stone' uses the fact that the blue colour of the sky is due to Rayleigh scattering of sunlight from the air molecules. Blue is more efficiently scattered than red, which is why the sky is blue, but there is also some polarization of the scattered light which is strongest at a scattering angle of 90 degrees. It was fun when in the Sahara to look up at the sky with my back to the sun while wearing polarized sun glasses. There in the sky, at an altitude about 90 degrees away from that of the sun, a large black hole could be seen as the horizontally polarized blue light was blocked by the glasses. This phenomenon is not much use as a navigation aid in the Sahara, of course, as the sun is not usually blocked by clouds. I have tried looking for the 'black hole' on cloudy days up here in Scotland using my polarized sun glasses, but I have to say with very limited success - in fact, no success at all. I have not heard of anyone actually using a 'sunstone' effectively as a means of navigation. But for the fact that the 'sun stone' was described in the Sagas no less than three times (see http://www.nordskip.com/vsagas.html ), I would put very little credence at all in this as an instrument of navigation. Geoffrey Kolbe --~--~---------~--~----~------------~-------~--~----~ Navigation List archive: www.fer3.com/arc To post, email NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---