In the North of the Arctic Circle, there is continuous daylight for months in the summer. Since the Vikings voyaged mostly in the summer (around the summer solstices) where there are very few stars, they did not rely much on the stars for navigation. Instead, they looked at the sun.
The amazing thing about the Vikings is that they were able maintain a stable course to cross the Atlantic Ocean, between 61st to 62nd degrees North on a due western course from Norway to Greenland. A task that is relatively tough during that era of time.
How they did it?? Well, they had the "solskuggefjøl" ,a sun shadow board, and the sun compass.
“ Solskuggefjøl"-a sun shadow board
This device is used to determine latitude. It’s a circular wooden board about 25-30cm in diameter and is kept in a bowl of water to stabilize it. The gnomon (vertical pole) at the centre can be used to set the time of the year. Concentric circles are marked on the board to represent different dates. The shadow of the noon sun is then observed. The shadow should reach a particular desired ring if the ship is on the correct latitude. If the shadow is over the line, the ship will be too far north; if it hasn’t reach the line, the ship is too far south.
The bearing dial of a sun compass:
Since the sun’s shadow from the gnomon at the middle of the disk describes different hyperbola at different times of the year, by rotating the disk till the shadow of the tip falls on a hyperbola that represent 62 degrees & the four week around summer solstice, we will be able to find out the general direction.
However, if the wrong curve is chosen, and the course becomes a little too north in the morning, it can be corrected by steering to a slightly more south direction, and the average direction will be right.
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