How did the Vikings find their way? The sagas mention shore-sighting birds. Some argue that Vikings had the magnetic compass long before the rest of Europe. Others claim they used the stars, forgetting that in the long days of the Norse cruising season, sunlight blots out the stars. Perhaps they used a sunstone to polarise sunlight and find their direction even when the sky was overcast, but it is more likely that, when overcast, the shadow thrown by a knife blade gave direction, see Figure 7.6.
In the early 1990s part of a 7cm wooden disk was found on an archaeological dig of Viking ruins in Uunartoq Fjord, Greenland, which has been identified as a form of sun compass.
A sun compass is an analemmatic sundial used to find direction rather than time. For crossing deserts in tanks and trucks sun compasses had a niche market until the introduction of GPS. A magnetic compass is useless in a vehicle unless the vehicle stops and the navigator walks away from it. Commercial sun compasses are set up for
7.6 Using Shadows to find the Direction of the Sun
different latitudes and different times of the year, but you can make a one-time Viking sun compass.
Before you set sail, take a piece of wood - circular looks best, square is fine. Fit a short gnomon in the centre. Place it in a suitably sunny spot, level it off, and spend one day marking the tip of the sun's shadow on the board at half-hourly intervals. At the end of the day, join the dots into a curved line. The shortest shadow is noon and this points north. Draw in the other compass points. You have a sun compass, see Figure 7.6b.
To find north during the day hold the board level and turn it until the sun's shadow touches the line. The north you drew now points north. There are serious limitations. The sun's shadow changes with its declination, so this sun compass is only good for a couple of weeks. Secondly it is, at most, accurate over a couple of degrees of latitude.
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