The sunstone and polarised skylight: ancient Viking navigational tools?

@article{Ropars2014TheSA,
  title={The sunstone and polarised skylight: ancient Viking navigational tools?},
  author={Guy Ropars and Vasudevan Lakshminarayanan and Albert Le Floch},
  journal={Contemporary Physics},
  year={2014},
  volume={55},
  pages={302 - 317}
}
Although the polarisation of the light was discovered at the beginning of the nineteenth century, the Vikings could have used the polarised light around the tenth century in their navigation to America, using a ‘sunstone’ evoked in the Icelandic Sagas. Indeed, the birefringence of the Iceland spar (calcite), a common crystal in Scandinavia, permits a simple observation of the axis of polarisation of the skylight at the zenith. From this, it is possible to guess the azimuth of a hidden Sun below… 

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