The Vikings were accomplished seafarers. Navigation was handled by
specially trained personnel who mostly navigated by the stars and the
sun. Sometimes they brought birds with them which they let go and then
followed to the nearest shore.
They had peloruses (astonishingly similar to the ones used today) and
the famous sun stone. A pelorus is a compass card that lists the bearings,
or directions, for the ship. The sun stone is a mineral found in Iceland
or Norway which could polarize the sun light. That way you could see where
the sun was even if it was cloudy and the sun itself was not visible to
the naked eye. The sun stone was thought to be a fraud, but later findings
make it clear that it actually worked.
Star: Viking navigators relied on the North Star, also known
as Polestar or Polaris, to chart the direction of their routes at night.
The North Star is the best way humans have of finding the location
of the north celestial pole. Vikings could use it to measure the
distance in degrees from north to south, which is called latitude.
They did this by measuring how high the North Star was from the
horizon and comparing it to the height of the North Star when
they were home.
The North Star was only useful, however, when Vikings were in
the northern hemisphere. As they moved toward the equator their
view of the North Star lost accuracy and could no longer be used
to locate the true distance to the north pole.
The Vikings created a number of tools that helped them used the
sun to determine latitude during the day.
Dial: The Vikings knew that the sun was always directly overhead
at noon. But at other times of the day they relied on a tool called a
bearing dial, or bearing circle, to determine the latitude of the sun.
The bearing dial was a small platform with a vertical pin in
the middle and a pointer that marked the course they were traveling.
When the sun shone on the bearing dial it created a shadow behind
the vertical pin. The Vikings marked the placement of those shadows
on the platform at all times of day so that they would always
be able to determine where they were and the direction in which
they were heading by looking at the shadow cast by the sun on
the bearing dial.
Shadow Board: At noon the Vikings used a tool called the sun
shadow board to double-check whether their ship was on the right course.
The sun shadow board was a circular wooden board about 250 to 300 millimeters
in diameter. In the center was a gnomon, the height of which could be
set to the time of the year. To keep the sun shadow board level, it was
placed in a bowl of water. The shadow of the noon sun was observed on
the board. A circle on the board showed the Viking sailors the line the
sun's shadow should reach if their ship was traveling on the desired latitude.
If the shadow was beyond the line, they knew the ship was too far north;
if the shadow was inside the line, the ship was moving too far south.
In this way the sun shadow board helped the Vikings to correct their course
This was important because even a small change in course could result
in their not reaching their planned destination. Sailing in cloudy weather
or fog was very risky, because the Vikings couldn't rely on the sun¹s
shadow to use the sun shadow board.
Stone: On overcast days the Vikings relied on the sun stone
to help them find the sun's position. This stone, made of a mineral called
Icelandic spar, would change color slightly as it was turned in the light.
A certain color marked the position of the sun even through fog and cloud.
The Vikings could only use the sun stone, however, when they were able
to see at least a hint of blue sky.
Seafarers watched the sun closely all year round and kept records
of its path through the heavens. Vikings in Iceland collected this information
in a table containing height measurements of the sun for the whole year.
They also noted where on the horizon the sun rose and set each day.
All the measurements from this table were put on a tool called
the semi-wheel. The Vikings looked to this tool to determine the
directions of north, south, east and west and to calculate latitude.
Finding direction is difficult during the day because the sun's
path across the sky is different during different seasons of the year.
Through careful observation, the Vikings learned that the sun's shadow
from the tip in the middle of a disk they called the sun compass would
describe different hyperbolas at different times of the year. The compass
was marked with all these hyperbolas. While at sea the Vikings would rotate
the disk until the shadow of the tip fell on the hyperbola for that time
of year. They were then able to determine their location at sea with an
accuracy of a few degrees at any time of day.