Sky-Polarimetric Viking Navigation

Horváth, Gábor; Farkas, Anna; Bernáth, Balázs

doi:10.1007/978-3-642-54718-8_25

Cited by 11 publications

(18 citation statements)

References 31 publications

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“…Our results suggest that this would only be possible when the degree of polarization was above an individual's per cent polarization threshold, which based on measurements of sky polarization would limit this to conditions of clear skies [ 55 , 56 ]. There is some evidence that Vikings may have used celestial polarization patterns as a navigational aid when crossing the north Atlantic [ 57 – 59 ]. Celestial polarization patterns could have been particularly helpful in northern latitudes where the twilight period, when the sun is below the horizon and the sky is too bright to see the stars, is particularly long [ 60 ].…”

Section: Discussionmentioning

confidence: 99%

Perceiving polarization with the naked eye: characterization of human polarization sensitivity

et al. 2015

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Like many animals, humans are sensitive to the polarization of light. We can detect the angle of polarization using an entoptic phenomenon called Haidinger's brushes, which is mediated by dichroic carotenoids in the macula lutea. While previous studies have characterized the spectral sensitivity of Haidinger's brushes, other aspects remain unexplored. We developed a novel methodology for presenting gratings in polarization-only contrast at varying degrees of polarization in order to measure the lower limits of human polarized light detection. Participants were, on average, able to perform the task down to a threshold of 56%, with some able to go as low as 23%. This makes humans the most sensitive vertebrate tested to date. Additionally, we quantified a nonlinear relationship between presented and perceived polarization angle when an observer is presented with a rotatable polarized light field. This result confirms a previous theoretical prediction of how uniaxial corneal birefringence impacts the perception of Haidinger's brushes. The rotational dynamics of Haidinger's brushes were then used to calculate corneal retardance. We suggest that psychophysical experiments, based upon the perception of polarized light, are amenable to the production of affordable technologies for self-assessment and longitudinal monitoring of visual dysfunctions such as age-related macular degeneration.

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Section: Discussionmentioning

confidence: 99%

Perceiving polarization with the naked eye: characterization of human polarization sensitivity

et al. 2015

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“…It is still unclear how they could maintain the correct direction without any advanced navigational tools such as a magnetic compass. According to some theories, they benefited from atmospheric optic navigational cues, for example crepuscular rays [3,[5][6][7] or Arctic mirages [8,9].…”

Section: Introductionmentioning

confidence: 99%

“…Sunstones are referred to in ancient Viking stories, sagas, and are described as tools that can be used to detect the position of the Sun even when it is covered by clouds or fog [7,16,17]. According to the theory, sunstones could possibly be dichroic cordierite, tourmaline and andalusite, for instance, or birefringent calcite (Icelandic spar) [18][19][20][21][22][23][24][25], through which the observer (navigator, always a male in the Viking age) can see the changes in the intensity of the transmitted linearly polarized skylight while he rotates the crystal in front of his eyes.…”

Section: Introductionmentioning

confidence: 99%

“…According to the theory, sunstones could possibly be dichroic cordierite, tourmaline and andalusite, for instance, or birefringent calcite (Icelandic spar) [18][19][20][21][22][23][24][25], through which the observer (navigator, always a male in the Viking age) can see the changes in the intensity of the transmitted linearly polarized skylight while he rotates the crystal in front of his eyes. The steps in this sky-polarimetric Viking navigation method are described in detail elsewhere [7,17,26,27].…”

Section: Introductionmentioning

confidence: 99%

“…Previously, we have measured by imaging polarimetry the atmospheric optical prerequisites of this navigation method under skies with different cloud and fog coverage [7,17,[28][29][30]. The accuracy of the first step has been measured in a laboratory experiment [27] and that of the second step in a planetarium experiment [26].…”

Section: Introductionmentioning

confidence: 99%

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North error estimation based on solar elevation errors in the third step of sky-polarimetric Viking navigation

et al. 2016

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The theory of sky-polarimetric Viking navigation has been widely accepted for decades without any information about the accuracy of this method. Previously, we have measured the accuracy of the first and second steps of this navigation method in psychophysical laboratory and planetarium experiments. Now, we have tested the accuracy of the third step in a planetarium experiment, assuming that the first and second steps are errorless. Using the fists of their outstretched arms, 10 test persons had to estimate the elevation angles (measured in numbers of fists and fingers) of black dots (representing the position of the occluded Sun) projected onto the planetarium dome. The test persons performed 2400 elevation estimations, 48% of which were more accurate than ±1°. We selected three test persons with the (i) largest and (ii) smallest elevation errors and (iii) highest standard deviation of the elevation error. From the errors of these three persons, we calculated their error function, from which the North errors (the angles with which they deviated from the geographical North) were determined for summer solstice and spring equinox, two specific dates of the Viking sailing period. The range of possible North errors Δ ω N was the lowest and highest at low and high solar elevations, respectively. At high elevations, the maximal Δ ω N was 35.6° and 73.7° at summer solstice and 23.8° and 43.9° at spring equinox for the best and worst test person (navigator), respectively. Thus, the best navigator was twice as good as the worst one. At solstice and equinox, high elevations occur the most frequently during the day, thus high North errors could occur more frequently than expected before. According to our findings, the ideal periods for sky-polarimetric Viking navigation are immediately after sunrise and before sunset, because the North errors are the lowest at low solar elevations.

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