Viking navigation was handled by specially trained men who used the stars and sun to aid in their voyages. While birds were brought along on some voyages to be let go in order to follow them to the nearest land, they relied on navigation tools called peloruses, the sun stone, the bearing dial, the sun shadow board, and the sun compass.
Primarily, the Vikings used the North Star or Polaris to help them navigate at night. Located in the night sky, directly over the north celestial pole, the distance from the North Star to the horizon was compared to the height of the star when they were at home. This measurement helped them to determine their latitude.
The pelorus, similar to the ones used today, was an instrument much like a mariner's compass, but without magnetic needles. It had two sight vanes and was mounted in such a way that the bearings of objects could be observed. The bearing dial or bearing circle was used to determine the latitude of the sun. It had a small platform with a vertical pin in the middle and a pointer, and it was used to track the position of the sun in the sky by marking the placement of shadows on the platform.
The sun shadow board was used at noon to double check whether the ship was on the correct course or not. It was placed in a bowl of water to keep it level and the gnomen, the pin in the center of the board, marked the shadow of the noon sun. Circles marked on the board gave the sailors an area in which they could travel and still remain within their desired latitude. If the shadow of the noon sun extended beyond the circle, they knew they had traveled too far north. If the shadow was inside the line, they were too far south. The sun shadow board's midday measurement helped the Vikings make course corrections each noon, but was of know use to the sailors in cloudy or foggy weather.
The sun stone was used on the days when fog or clouds obscured the sun. The stone, a mineral called Icelandic spar, would change color as it was turned in the light. A certain color would indicate the position of the sun through the fog or clouds but could only be used when there was at least a sliver of blue sky. The semi-wheel was a chart that recorded the year round observations of the sun and measurements of its positions. The Vikings of Iceland collected this data, also noting where on the horizon the sun rose and set each day. This collection of information was used to determine their latitude as well as the cardinal directions, North, South, East and West.
The sun compass recorded the different paths the sun took across the sky during the different seasons of the year. By drawing these different hyperbolas on the face of the sun compass, the Vikings had a record of the sun's position for each time of year. They were able to determine, with great accuracy and at any time of day, their position at sea by rotating the disk of the sun compass until the shadow of the tip in the center of the compass fell on the hyperbola for that time of year.