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Title:
DEVICE FOR DETECTING THE DIRECTION OF A HIDDEN SUN USING A BIREFRINGENT DEPOLARIZER
Document Type and Number:
WIPO Patent Application WO/2013/057582
Kind Code:
A4
Abstract:
Vikings sailed across the Norwegian Sea and the Northern Atlantic Ocean along latitude 61 ° N (Thirslund, S. 2007: Viking navigation: sun-compass guided Norsemen to America, The Viking Ship Museum) between Norway, Island, Greenland and North America in the 9th and 10th centuries. They sailed through thousand kilometres of open water without using a magnetic compass, which has been only introduced in Europe in about the 13th century. Anyway, it would not have helped much, because near polar regions any magnetic measurements are affected by errors. Vikings sailed from May to October, during long days reaching about 20 hours, preventing them to use the stars. Thus they remained with the use of the sun. Unfortunately, at these latitudes, the sun stays several hours below the horizon, or can be hidden by clouds or by fog banks near the horizon. In the Icelandic sagas written in the 12th and 13th centuries, a sunstone is mentioned to determine the sun direction. As suggested by Ramskou (Ramskou, T. 1967: Solstenen, Skalk 2, 16-17) the sunstone can use the sky polarization. Note that many animals use the sky polarization for their navigation, like honeybees for instance (Horvdth, G; Varjii, D. 2004: Polarized Light in Animal Vision - Polarization Patterns in Nature, Springer-Verlag, Heidelberg - Berlin - New York). Indeed, we now know that the light scattered by the sky is polarized, due to the Rayleigh scattering (Hoeppe, G 2007: Why the sky is blue. Princeton, NJ: Princeton University Press; Coulson, K. L. 1988: Polarization and Intensity of Light in the Atmosphere, A. Deepak Publishing, Hampton, Virginia, USA), and therefore it can give the sun direction even when it is below the horizon or not directly observable.

Inventors:
LE FLOCH ALBERT (FR)
ROPARS GUY (FR)
Application Number:
PCT/IB2012/002572
Publication Date:
June 27, 2013
Filing Date:
October 17, 2012
Export Citation:
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Assignee:
LE FLOCH ALBERT (FR)
ROPARS GUY (FR)
International Classes:
G01C21/02
Attorney, Agent or Firm:
LE FLOCH, Albert (Rennes, Rennes, FR)
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