Sky-polarimetric viking navigation

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 horizonwith 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 showmodern navigation instruments that operate in a similar principle.Weinvestigate 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.