OSA's Digital Library

Journal of the Optical Society of America A

Journal of the Optical Society of America A

| OPTICS, IMAGE SCIENCE, AND VISION

  • Vol. 22, Iss. 6 — Jun. 1, 2005
  • pp: 1023–1034

Psychophysical study of the visual sun location in pictures of cloudy and twilight skies inspired by Viking navigation

András Barta, Gábor Horváth, and Victor Benno Meyer-Rochow  »View Author Affiliations


JOSA A, Vol. 22, Issue 6, pp. 1023-1034 (2005)
http://dx.doi.org/10.1364/JOSAA.22.001023


View Full Text Article

Acrobat PDF (451 KB)





Browse Journals / Lookup Meetings

Browse by Journal and Year


   


Lookup Conference Papers

Close Browse Journals / Lookup Meetings

Article Tools

Share
Citations

Abstract

In the late 1960s it was hypothesized that Vikings had been able to navigate the open seas, even when the sun was occluded by clouds or below the sea horizon, by using the angle of polarization of skylight. To detect the direction of skylight polarization, they were thought to have made use of birefringent crystals, called "sunstones," and a large part of the scientific community still firmly believe that Vikings were capable of polarimetric navigation. However, there are some critics who treat the usefulness of skylight polarization for orientation under partly cloudy or twilight conditions with extreme skepticism. One of their counterarguments has been the assumption that solar positions or solar azimuth directions could be estimated quite accurately by the naked eye, even if the sun was behind clouds or below the sea horizon. Thus under partly cloudy or twilight conditions there might have been no serious need for a polarimetric method to determine the position of the sun. The aim of our study was to test quantitatively the validity of this qualitative counterargument. In our psychophysical laboratory experiments, test subjects were confronted with numerous 180° field-of-view color photographs of partly cloudy skies with the sun occluded by clouds or of twilight skies with the sun below the horizon. The task of the subjects was to guess the position or the azimuth direction of the invisible sun with the naked eye. We calculated means and standard deviations of the estimated solar positions and azimuth angles to characterize the accuracy of the visual sun location. Our data do not support the common belief that the invisible sun can be located quite accurately from the celestial brightness and/or color patterns under cloudy or twilight conditions. Although our results underestimate the accuracy of visual sun location by experienced Viking navigators, the mentioned counterargument cannot be taken seriously as a valid criticism of the theory of the alleged polarimetric Viking navigation. Our results, however, do not bear on the polarimetric theory itself.

© 2005 Optical Society of America

OCIS Codes
(000.4930) General : Other topics of general interest
(010.1290) Atmospheric and oceanic optics : Atmospheric optics
(010.3920) Atmospheric and oceanic optics : Meteorology
(330.5510) Vision, color, and visual optics : Psychophysics
(330.7310) Vision, color, and visual optics : Vision

Citation
András Barta, Gábor Horváth, and Victor Benno Meyer-Rochow, "Psychophysical study of the visual sun location in pictures of cloudy and twilight skies inspired by Viking navigation," J. Opt. Soc. Am. A 22, 1023-1034 (2005)
http://www.opticsinfobase.org/josaa/abstract.cfm?URI=josaa-22-6-1023

You do not have subscription access to this journal. Citation lists with outbound citation links are available to subscribers only. You may subscribe either as an OSA member, or as an authorized user of your institution.

Contact your librarian or system administrator
or
Log in to access OSA Member Subscription

You do not have subscription access to this journal. Cited by links are available to subscribers only. You may subscribe either as an OSA member, or as an authorized user of your institution.

Contact your librarian or system administrator
or
Log in to access OSA Member Subscription

You do not have subscription access to this journal. Article level metrics are available to subscribers only. You may subscribe either as an OSA member, or as an authorized user of your institution.

Contact your librarian or system administrator
or
Log in to access OSA Member Subscription

« Previous Article  |  Next Article »

OSA is a member of CrossRef.

CrossCheck Deposited