Orientation with a Viking sun-compass, a shadow-stick, and two calcite sunstones under various weather conditions

Balázs Bernáth, Miklós Blahó, Ádám Egri, András Barta, György Kriska, Gábor Horváth
2013 Applied Optics  
It is widely accepted that Vikings used sun-compasses to derive true directions from the cast shadow of a gnomon. It has been hypothesized that when a cast shadow was not formed, Viking navigators relied on crude skylight polarimetry with the aid of dichroic or birefringent crystals, called "sunstones." We demonstrate here that a simple tool, that we call "shadow-stick," could have allowed orientation by a sun-compass with satisfying accuracy when shadows were not formed, but the sun position
more » ... the sun position could have reliably been estimated. In field tests, we performed orientation trials with a set composed of a sun-compass, two calcite sunstones, and a shadow-stick. We show here that such a set could have been an effective orientation tool for Vikings only when clear, blue patches of the sky were visible.
doi:10.1364/ao.52.006185 pmid:24085076 fatcat:dwwmndj3obahhonhgyuuxd3yqi