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    Re: New thoughts about the Viking sun compass
    From: Geoffrey Kolbe
    Date: 2013 May 04, 16:43 +0100
    Hello Wolfgang

    Ah, but it was not that sun compass ;-)

    The sun compass referred to in the link I gave was a small 'sundial' like device, with a short gnomon casting a shadow onto a wooden disk.

    There was a very interesting program on the TV some years ago, about the voyage of a reconstructed Viking trading ship across the North Sea from Norway to the Shetlands. The navigator was Sir Robin Knox-Johnston, and he is nobody's fool. Sir Robin had constructed a 'sun compass' based on the item found on Greenland, which is the subject of the link I gave. Sir Robin's compass was calibrated on land on the day before the voyage, by setting the 'compass' to point North. Then, the point of the gnomon's shadow was plotted at regular intervals on the disc throughout the day. A curve was then drawn through the plotted points.

    The method used to find the course during the voyage was simply to hold the sun compass horizontal and then rotate it until the shadow of the gnomon touched the inscribed curve. North on the compass was then pointing North in actuality. Everyone was amazed how accurate it was and the GPS unit taken as back-up reserve remained under lock and key! The Shetlands was raised without incident.

    Geoffrey
       
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