(a) The wooden disc fragment (found in southern Greenland) onto which the Viking navigators scratched some hyperbolic curves [1]. (b) The reconstructed sundial used by the Vikings for navigation on the open sea. The left, gray part of the disc has not been found. (c) Three-dimensional drawing of the Viking sundial with a conical vertical gnomon and its shadow, the endpoint of which touches the hyperbola scratched into the horizontal wooden disc. (d) Sky-polarimetric navigation by Vikings can only function if the direction of skylight polarization (symbolized by double-headed arrows) is perpendicular to the plane of scattering (determined by the sun, the observer and the celestial point observed).
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(a) The wooden disc fragment (found in southern Greenland) onto which the Viking navigators scratched some hyperbolic curves [1]. (b) The reconstructed sundial used by the Vikings for navigation on the open sea. The left, gray part of the disc has not been found. (c) Three-dimensional drawing of the Viking sundial with a conical vertical gnomon and its shadow, the endpoint of which touches the hyperbola scratched into the horizontal wooden disc. (d) Sky-polarimetric navigation by Vikings can only function if the direction of skylight polarization (symbolized by double-headed arrows) is perpendicular to the plane of scattering (determined by the sun, the observer and the celestial point observed).
Zoom Info
(a) The wooden disc fragment (found in southern Greenland) onto which the Viking navigators scratched some hyperbolic curves [1]. (b) The reconstructed sundial used by the Vikings for navigation on the open sea. The left, gray part of the disc has not been found. (c) Three-dimensional drawing of the Viking sundial with a conical vertical gnomon and its shadow, the endpoint of which touches the hyperbola scratched into the horizontal wooden disc. (d) Sky-polarimetric navigation by Vikings can only function if the direction of skylight polarization (symbolized by double-headed arrows) is perpendicular to the plane of scattering (determined by the sun, the observer and the celestial point observed).
Zoom Info

(a) The wooden disc fragment (found in southern Greenland) onto which the Viking navigators scratched some hyperbolic curves [1]. (b) The reconstructed sundial used by the Vikings for navigation on the open sea. The left, gray part of the disc has not been found. (c) Three-dimensional drawing of the Viking sundial with a conical vertical gnomon and its shadow, the endpoint of which touches the hyperbola scratched into the horizontal wooden disc. (d) Sky-polarimetric navigation by Vikings can only function if the direction of skylight polarization (symbolized by double-headed arrows) is perpendicular to the plane of scattering (determined by the sun, the observer and the celestial point observed).

From the Saga of King Olaf the Holy: 
King Olaf the Holy
The weather was thick and snowy as Sigurður had predicted. Then the king summoned Sigurður and Dagur (Rauðúlfur’s sons) to him. The king made people look out and they could nowhere see a clear sky. Then he asked Sigurður to tell where the sun was at that time. He gave a clear assertion. Then the king made them fetch the solar stone and held it up and saw where light radiated from the stone and thus directly verified Sigurður’s prediction.

From the Saga of King Olaf the Holy:


King Olaf the Holy

The weather was thick and snowy as Sigurður had predicted. Then the king summoned Sigurður and Dagur (Rauðúlfur’s sons) to him. The king made people look out and they could nowhere see a clear sky. Then he asked Sigurður to tell where the sun was at that time. He gave a clear assertion. Then the king made them fetch the solar stone and held it up and saw where light radiated from the stone and thus directly verified Sigurður’s prediction.
This geometrical Viking camp on the Jutland Peninsula of Denmark extends some 130 yards in diameter.

This geometrical Viking camp on the Jutland Peninsula of Denmark extends some 130 yards in diameter.