Sky-Polarimetric Viking Navigation
It is a widely discussed and regularly cited theory that Viking navigators might have been able to locate the position of the sun occluded by clouds or below the horizon with a mysterious birefringent or dichroic crystal, the sunstone, on the basis of the
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Sky-Polarimetric Viking Navigation Ga´bor Horva´th, Alexandra Farkas, and Bala´zs Berna´th
Abstract It is a widely discussed and regularly cited theory that Viking navigators might have been able to locate the position of the sun occluded by clouds or below the horizon with a mysterious birefringent or dichroic crystal, the sunstone, on the basis of the pattern of skylight polarisation. In this chapter we describe the steps and the experimentally tested efficiency of this sky-polarimetric navigation method, and we show modern navigation instruments that operate in a similar principle. We investigate the atmospheric optical prerequisites of sky-polarimetric Viking navigation, looking for the ideal weather conditions, under which sunstones could be used for this navigational task. We also discuss other hypothesised Viking navigation instruments, like the horizon board and the sun compass or twilight board. Finally, we consider the Medieval Norse sailing routes and some alternative atmospheric optical navigation cues, which also could help during the long-time marine voyage of Viking seafarers.
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Introduction
It is a frequently cited theory that Vikings—seafaring Norse people flourishing from the eighth to the twelfth century—might have been able to navigate by means of the polarisation pattern of the sky. The theory was first outlined by Ramskou (1969) as an analogy of a modern polarimetric navigational instrument (the Kollsman’s polarised G. Horva´th (*) • A. Farkas Environmental Optics Laboratory, Department of Biological Physics, Physical Institute, Eotvos University, Pazmany setany 1, 1117, Budapest, Hungary e-mail: [email protected]; [email protected] B. Berna´th Institute of Biology, University of Neuchatel, Rue Emile-Argand 11, CH-2000, Neuchatel, Switzerland e-mail: [email protected] G. Horva´th (ed.), Polarized Light and Polarization Vision in Animal Sciences, Springer Series in Vision Research 2, DOI 10.1007/978-3-642-54718-8_25, © Springer-Verlag Berlin Heidelberg 2014
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skylight compass, type no. 2029B-01) used through the preceding decades on airplanes flying above the North Pole. The alleged medieval tools for it are the mysterious ‘sunstones’, but their role in the Viking navigation discipline is rather a disputed theory than a proven fact. The sole written source founding the theory is a scene in the Rauðu´lfs þa´ttur, that is, a saga on Olaf II Haraldsson (995–29 July 1030), also known as King Olaf, the Holy. A Viking named Sigurður claims that he is ‘able to discern the motion of heavenly bodies, those which he sees, and to know the stars which mark the hours, so that he will know time length at day and night although he does not see the celestial bodies, and still he knows how to discern all hours both day and night’. Later on he is tried by King Olaf: ‘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
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