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How could the Viking Sun compass be used with sunstones before and after sunset? Twilight board as a new interpretation of the Uunartoq artefact fragment

Bernath, Balazs; Farkas, Alexandra; Szaz, Denes; Blaho, Miklos; Egri, Adam; Barta, Andras; Åkesson, Susanne LU and Horvath, Gabor (2014) In Royal Society of London. Proceedings A. Mathematical, Physical and Engineering Sciences 470(2166).
Abstract
Vikings routinely crossed the North Atlantic without amagnetic compass and left their mark on lands as far away as Greenland, Newfoundland and Baffin Island. Based on an eleventh-century dial fragment artefact, found at Uunartoq in Greenland, it is widely accepted that they sailed along chosen latitudes using primitive Sun compasses. Such instruments were tested on sea and proved to be efficient hand-held navigation tools, but the dimensions and incisions of the Uunartoq find are far from optimal in this role. On the basis of the sagasmentioning sunstones, incompatible hypotheses were formed for Viking solar navigation procedures and primitive skylight polarimetry with dichroic or birefringent crystals. We describe here a previously... (More)
Vikings routinely crossed the North Atlantic without amagnetic compass and left their mark on lands as far away as Greenland, Newfoundland and Baffin Island. Based on an eleventh-century dial fragment artefact, found at Uunartoq in Greenland, it is widely accepted that they sailed along chosen latitudes using primitive Sun compasses. Such instruments were tested on sea and proved to be efficient hand-held navigation tools, but the dimensions and incisions of the Uunartoq find are far from optimal in this role. On the basis of the sagasmentioning sunstones, incompatible hypotheses were formed for Viking solar navigation procedures and primitive skylight polarimetry with dichroic or birefringent crystals. We describe here a previously unconceived method of navigation based on the Uunartoq artefact functioning as a 'twilight board', which is a combination of a horizon board and a Sun compass optimized for use when the Sun is close to the horizon. We deduced an appropriate solar navigation procedure using a twilight board, a shadow-stick and birefringent crystals, which bring together earlier suggested methods in harmony and provide a true skylight compass function. This could have allowed Vikings to navigate around the clock, to use the artefact dial as a Sun compass during long parts of the day and to use skylight polarization patterns in the twilight period. In field tests, we found that true north could be appointed with such a medieval skylight compass with an error of about +/- 4 degrees when the artificially occluded Sun had elevation angles between +10 degrees and -8 degrees relative to the horizon. Our interpretation allows us to assign exact dates to the gnomonic lines on the artefact and outlines the schedule of the merchant ships that sustained the Viking colony in Greenland a millennium ago. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
Viking navigation, sunstone, horizon board, twilight board, skylight, compass, sky polarization
in
Royal Society of London. Proceedings A. Mathematical, Physical and Engineering Sciences
volume
470
issue
2166
publisher
Royal Society
external identifiers
  • wos:000335326400006
  • pmid:24910520
  • scopus:84899798488
ISSN
1364-5021
DOI
10.1098/rspa.2013.0787
project
CAnMove
language
English
LU publication?
yes
id
b2ba7d7f-3398-4742-9ad0-fbd6828db77c (old id 4482319)
date added to LUP
2014-06-19 13:43:26
date last changed
2017-10-22 04:07:33
@article{b2ba7d7f-3398-4742-9ad0-fbd6828db77c,
  abstract     = {Vikings routinely crossed the North Atlantic without amagnetic compass and left their mark on lands as far away as Greenland, Newfoundland and Baffin Island. Based on an eleventh-century dial fragment artefact, found at Uunartoq in Greenland, it is widely accepted that they sailed along chosen latitudes using primitive Sun compasses. Such instruments were tested on sea and proved to be efficient hand-held navigation tools, but the dimensions and incisions of the Uunartoq find are far from optimal in this role. On the basis of the sagasmentioning sunstones, incompatible hypotheses were formed for Viking solar navigation procedures and primitive skylight polarimetry with dichroic or birefringent crystals. We describe here a previously unconceived method of navigation based on the Uunartoq artefact functioning as a 'twilight board', which is a combination of a horizon board and a Sun compass optimized for use when the Sun is close to the horizon. We deduced an appropriate solar navigation procedure using a twilight board, a shadow-stick and birefringent crystals, which bring together earlier suggested methods in harmony and provide a true skylight compass function. This could have allowed Vikings to navigate around the clock, to use the artefact dial as a Sun compass during long parts of the day and to use skylight polarization patterns in the twilight period. In field tests, we found that true north could be appointed with such a medieval skylight compass with an error of about +/- 4 degrees when the artificially occluded Sun had elevation angles between +10 degrees and -8 degrees relative to the horizon. Our interpretation allows us to assign exact dates to the gnomonic lines on the artefact and outlines the schedule of the merchant ships that sustained the Viking colony in Greenland a millennium ago.},
  articleno    = {20130787},
  author       = {Bernath, Balazs and Farkas, Alexandra and Szaz, Denes and Blaho, Miklos and Egri, Adam and Barta, Andras and Åkesson, Susanne and Horvath, Gabor},
  issn         = {1364-5021},
  keyword      = {Viking navigation,sunstone,horizon board,twilight board,skylight,compass,sky polarization},
  language     = {eng},
  number       = {2166},
  publisher    = {Royal Society},
  series       = {Royal Society of London. Proceedings A. Mathematical, Physical and Engineering Sciences},
  title        = {How could the Viking Sun compass be used with sunstones before and after sunset? Twilight board as a new interpretation of the Uunartoq artefact fragment},
  url          = {http://dx.doi.org/10.1098/rspa.2013.0787},
  volume       = {470},
  year         = {2014},
}