Sunstone (Vikings)
According to various traditions from the Viking Age, a sun stone ( sólsteinn ) served as a navigation aid in cloudy skies, fog or dusk .
The seafarers of the Viking Age mostly stayed close to the coast and orientated themselves mainly on landmarks and the position of the sun , possibly also using a sun compass .
Orientation based only on the position of the sun and without an exact time reaches its limits in the polar summer, when the sun is always visible. During the astronomical twilight , orientation to the stars is largely possible (not in polar summer), but much more difficult, since astronomical knowledge as well as the calendar date and the determination of the night time are also decisive.
The skies are often overcast on the North Sea , where the Vikings sailed or rowed a good 1000 years ago . In polar winter the sun appears north of 67.41 ° latitude, at least at the winter solstice, just below the horizon , so that twilight then prevails (only north of 73.2 ° latitude is it constantly too dark to read the newspaper in polar winter, but the Vikings moved in these polar regions probably not at all).
According to tradition, the Vikings are said to have owned a sunstone with which they could determine the exact position of the sun even when the sky was overcast. There are very different written references for this, for example in the Icelandic code of Grágás . The best-known tradition is that King Olav the Saint checked the position of the sun by his host Sigurðr with the help of such a sólsteinn when the snow was blowing and the sky was overcast. A working “sun stone” on a rotating disc is exhibited in the Viking Ship Museum Roskilde near Copenhagen.
There are several approaches to assign a real mineral to this story. Two theories about crystalline material and how a sunstone works:
- Use of polarization filters to recognize a polarization pattern in the largely overcast daytime sky
- Use of birefringence to identify the main light source in the cloudy daytime sky
Overall, however, it can be assumed that the Vikings used a mixture of different navigational aids: sailing along the coasts, broad sailing, the àttir system with the help of shipping routes, the sun compass and the help of sunstones. (see web link below)
Use of polarization filters
One interpretation is that the sunstone was a crystal that acts as a polarization filter.
Polarization pattern
Sunlight is initially unpolarized, which means that the individual waves within a sunbeam are statistically distributed in terms of their properties. By Rayleigh scattering occurs in the atmosphere polarized light. This strikes an observer at right angles to the incident sunlight, from a very wide semicircle (part of the circle section is below the horizon) around the position of the sun.
Perception as Haidinger tufts
The human eye cannot differentiate between different vibration levels of polarized light when viewed directly.
However, if an observer stares at a polarization pattern for a few seconds and then changes the posture of the head a little without changing the direction of his gaze, with some practice a diffuse yellow or blue appearance can be perceived.
Detection of the polarization pattern through polarization filters
When looking through a polarization filter, polarized light can be identified by turning it on the basis of the reduced light transmission and thus allows a darker large semicircle to be seen around the position of the sun. Convincing representations of the polarization pattern of a semicircle are complex, because they are overlaid by direct sunlight and other scattering. Partly cloud-free parts of the sky could make it possible to perceive the polarization pattern and to determine the position of the sun. This method would reach its limits in thick fog.
Natural polarizing filters
Cordierite , which Thorkild Ramskou referred to as the sólsteinn, offers the possibility of recognizing the celestial polarization pattern as long as there is a larger uncovered blue area of the sky, preferably at the zenith, while the (low) sun can be covered.
Current knowledge
It is controversial whether the Vikings or other seafarers used polarization filters to determine the position of the sun. There is no recognized source to prove this beyond any doubt.
When the sky is uncovered, the experienced observer can even recognize a sky polarization pattern without aids during sunrise or sunset, but this does not provide any additional useful information for navigation. However, it allows the complicated application of a polarization filter to be practiced for this observation.
Some insects can determine the position of the sun based on the polarization pattern of the partially covered daytime sky (e.g. bees according to research by Karl von Frisch ).
Use of birefringence
By refracting light with a birefringent crystal such as calcite ( calcite ), the incident light beam is split into two bundles of light with different strengths and polarization directions. By turning and turning the stone can be aligned so that the two light beams are equally strong. The viewing direction then points exactly in the direction of the light source, i.e. the sun.
Kalkspat or calcite is a mineral that occurs more frequently in Scandinavia. One such stone was found in the wreckage of an Elizabethan warship that sank in 1592 off the Channel Island of Alderney . The fact that the sunstone was still carried on board a ship in the 16th century - centuries after the invention of the compass - is explained by the scientists that little was known about how the compass worked at that time.
The application described can be learned quickly. However, it is debatable whether the Vikings or other seafarers used birefringent minerals to determine the position of the sun. There is no recognized source to prove this beyond any doubt.
assessment
There is no source that proves beyond any doubt that a sólsteinn was carried on board by the Vikings.
A determination of the position of the sun with a completely overcast sky and light drifting snow with the help of a natural sólsteinn as in tradition is not possible with the help of a polarization filter or a birefringent mineral, but probably a theatricality of the legends. But both methods could be used with partial cloudiness and light, cloudy weather, the polarization filter also with the sun just below the horizon.
literature
- Leif K. Karlsen: Secrets of the Viking Navigator. One Earth Press, 2003 ISBN 0-9721515-0-8
- Uwe Schnall: Navigation of the Vikings (Writings of the German Maritime Museum, Vol. 6), Eschwege 1975, ISBN 3-921909-73-2 .
- R Hegedüs, S Åkesson, R Wehner, G Horváth: Could Vikings have navigated under foggy and cloudy conditions by skylight polarization? On the atmospheric optical prerequisites of polarimetric Viking navigation under foggy and cloudy skies . Proceedings of the Royal Society A, 2007, Vol. 463 No. 2080, pp. 1081-1095.
Web links
- Leif K. Karlsen: Viking Navigation Using the Sunstone, Polarized Light and the Horizon Board http://www.oneearthpress.com/pdf/nav_notes.pdf ( Memento from December 12, 2014 in the Internet Archive ) December 12, 2014
- The Viking “sun stone” could exist science.orf.at
- Focus Online discovered the legendary “sun stone” of the Vikings on November 2, 2011
- Calcite instead of compass: researchers unravel the Vikings' sun stone Spiegel Online from March 7, 2013
- Legendary Viking Sunstone Navigation: Solved , November 2nd, 2011 (and the reference to Haidinger tufts )
- How the Vikings crossed the Atlantic without a compass , Tages-Anzeiger from May 3, 2018
- How did the Vikings steer their ships across the ocean? , Article on the navigation aids of the Vikings by Anthony Robards, published in February 2016 in scienceblog.at
Individual evidence
- ^ Uwe Schnall: Navigation of the Vikings. Writings of the German Maritime Museum 6. Hamburg, 1975, p. 87 ff.
- ↑ Historical References to Sunstones ( Memento of April 24, 2012 in the Internet Archive ), from Leif K. Karlsen: "Secrets of the Viking Navigators."
- ↑ Ramón Hegedüs, et al. : Could Vikings have navigated under foggy and cloudy conditions by skylight polarization? On the atmospheric optical prerequisites of polarimetric Viking navigation under foggy and cloudy skies . In: Proc. R. Soc. A . 463, No. 2080, 2007, pp. 1081-1095. doi : 10.1098 / rspa.2007.1811 .
- ↑ Polarized scattered light from the sky
- ↑ Navigation: Vikings could have used sunstones. In: Spiegel Online . February 7, 2007, accessed June 10, 2018 .
- ↑ Thorkild Ramskou: Solstenen . In: Tidskriftet Skalk, 1967, No. 2.
- ^ Leif K. Karlsen: Viking navigation using the sunstone, polarized light and the horizon board. Navigation Notes, Vol. 93, p. 5.
- ↑ http://www.scinexx.de/wissen-aktuell-14056-2011-11-02.html
- ↑ http://rspa.royalsocietypublishing.org/content/early/2011/10/28/rspa.2011.0369
- ↑ Der Spiegel : Sunstones could have shown Vikings the sea route from November 2, 2011, accessed July 29, 2016.