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

Bernáth, B. and Blahó, M. and Egri, Ádám and Barta, A. and Kriska, György (2013) Orientation with a Viking sun-compass, a shadow-stick, and two calcite sunstones under various weather conditions. APPLIED OPTICS (2004-), 52 (25). pp. 6185-6194. ISSN 1559-128X

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Abstract

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 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.

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