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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

Hegedus, R; Åkesson, Susanne LU ; Wehner, R and Horvath, G (2007) In Royal Society of London. Proceedings A. Mathematical, Physical and Engineering Sciences 463(2080). p.1081-1095
Abstract
In sunshine, the Vikings navigated on the open sea using sundials. According to a widespread hypothesis, when the Sun was occluded by fog or clouds the Vikings might have navigated by skylight polarization detected with an enigmatic birefringent crystal (sunstone). There are two atmospheric optical prerequisites for this alleged polarimetric Viking navigation under foggy/cloudy skies: (1) the degree of linear polarization p of skylight should be high enough and (2) at a given Sun position, the pattern of the angle of polarization a of the foggy/cloudy sky should be similar to that of the clear sky. Until now, these prerequisites have not been investigated. Using full-sky imaging polarimetry, we measured the p- and a-patterns of Arctic... (More)
In sunshine, the Vikings navigated on the open sea using sundials. According to a widespread hypothesis, when the Sun was occluded by fog or clouds the Vikings might have navigated by skylight polarization detected with an enigmatic birefringent crystal (sunstone). There are two atmospheric optical prerequisites for this alleged polarimetric Viking navigation under foggy/cloudy skies: (1) the degree of linear polarization p of skylight should be high enough and (2) at a given Sun position, the pattern of the angle of polarization a of the foggy/cloudy sky should be similar to that of the clear sky. Until now, these prerequisites have not been investigated. Using full-sky imaging polarimetry, we measured the p- and a-patterns of Arctic foggy and cloudy skies when the Sun was invisible. These patterns were compared with the polarization patterns of clear Arctic skies. We show here that although prerequisite (2) is always fulfilled under both foggy and cloudy conditions, if the fog layer is illuminated by direct sunlight, prerequisite (1) is usually satisfied only for cloudy skies. In sunlit fog, the Vikings could have navigated by polarization only, if p of light from the foggy sky was sufficiently high. (Less)
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author
organization
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type
Contribution to journal
publication status
published
subject
in
Royal Society of London. Proceedings A. Mathematical, Physical and Engineering Sciences
volume
463
issue
2080
pages
1081 - 1095
publisher
Royal Society
external identifiers
  • wos:000244255800011
  • scopus:35948984647
ISSN
1364-5021
DOI
10.1098/rspa.2007.1811
language
English
LU publication?
yes
id
343718c8-b43f-4af8-bfbe-ed8ccaf545b2 (old id 167141)
date added to LUP
2007-06-26 08:29:27
date last changed
2017-10-22 04:43:29
@article{343718c8-b43f-4af8-bfbe-ed8ccaf545b2,
  abstract     = {In sunshine, the Vikings navigated on the open sea using sundials. According to a widespread hypothesis, when the Sun was occluded by fog or clouds the Vikings might have navigated by skylight polarization detected with an enigmatic birefringent crystal (sunstone). There are two atmospheric optical prerequisites for this alleged polarimetric Viking navigation under foggy/cloudy skies: (1) the degree of linear polarization p of skylight should be high enough and (2) at a given Sun position, the pattern of the angle of polarization a of the foggy/cloudy sky should be similar to that of the clear sky. Until now, these prerequisites have not been investigated. Using full-sky imaging polarimetry, we measured the p- and a-patterns of Arctic foggy and cloudy skies when the Sun was invisible. These patterns were compared with the polarization patterns of clear Arctic skies. We show here that although prerequisite (2) is always fulfilled under both foggy and cloudy conditions, if the fog layer is illuminated by direct sunlight, prerequisite (1) is usually satisfied only for cloudy skies. In sunlit fog, the Vikings could have navigated by polarization only, if p of light from the foggy sky was sufficiently high.},
  author       = {Hegedus, R and Åkesson, Susanne and Wehner, R and Horvath, G},
  issn         = {1364-5021},
  language     = {eng},
  number       = {2080},
  pages        = {1081--1095},
  publisher    = {Royal Society},
  series       = {Royal Society of London. Proceedings A. Mathematical, Physical and Engineering Sciences},
  title        = {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},
  url          = {http://dx.doi.org/10.1098/rspa.2007.1811},
  volume       = {463},
  year         = {2007},
}