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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

Author:
  • Balazs Bernath
  • Alexandra Farkas
  • Denes Szaz
  • Miklos Blaho
  • Adam Egri
  • Andras Barta
  • Susanne Åkesson
  • Gabor Horvath
Publishing year: 2014
Language: English
Publication/Series: Royal Society of London. Proceedings A. Mathematical, Physical and Engineering Sciences
Volume: 470
Issue: 2166
Document type: Journal article
Publisher: Royal Society

Abstract english

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.

Keywords

  • Biological Sciences
  • Viking navigation
  • sunstone
  • horizon board
  • twilight board
  • skylight
  • compass
  • sky polarization

Other

Published
  • CAnMove
  • ISSN: 1364-5021
Susanne Åkesson
E-mail: susanne [dot] akesson [at] biol [dot] lu [dot] se

Professor

Evolutionary ecology

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