 |
| Source: istockphoto |
Vikings from Scandinavia were traders, explored
new land and settled in areas far from their homeland in Northern Europe. They
inhabited Iceland and southern Greenland and they even discovered North
Americas long before Columbus set his foot on the land located so far away in the west. From spring
to autumn the Vikings were engaging in trading trips and routinely crossed the
North Atlantic in their oak ships without guidance from a magnetic compass. Viking
settlements were raised as far west and north-west as south Greenland,
Newfoundland and Baffin Island. To reach these distant locations from
Scandinavia and more closely from Iceland, it is widely accepted that they sailed along chosen
latitudes using primitive Sun compasses. An eleventh-century dial fragment
artefact, found at Uunartoq in Greenland has been suggested to be a fragment of
a navigation instrument used by the early settlers. Instruments of this type
has been tested on sea crossings and proved to be efficient hand-held navigation
tools, but the dimensions and incisions of the Uunartoq find are far from
optimal in this role. On the basis of the sagas mentioning sunstones,
incompatible hypotheses were formed for Viking solar navigation procedures and
primitive skylight polarimetry with dichroic or birefringent crystals.
 |
| The Uunartoq artefact from Greenland. Source: Sören Thirslund. |
 |
| The Uunatoq artefact is suggested by us to be used as a combined Sun compass and horizon board (a "twilight board") and may have been used around the clock at northern latitudes (from Bernáth et al. 2014, Proc R Soc A). |
In a recent study published in Proc R Soc A
(Bernáth et al. 2014), we describe a previously unconceived method of navigation
based on the Uunartoq artefact functioning as a ‘twilight board’, which is a
combination of a horizon board and a Sun compass optimized for use when the Sun
is close to the horizon. We deduced an appropriate solar navigation procedure
using a twilight board, a shadow-stick and birefringent crystals, which bring together
earlier suggested methods in harmony and provide a true skylight compass
function. This could have allowed Vikings to navigate around the clock, to use
the artefact dial as a Sun compass during long parts of the day and to use
skylight polarization patterns in the twilight period. In field tests, we found
that true north could be appointed with such a medieval skylight compass with
an error of about ±4◦ when the artificially occluded Sun had elevation angles
between +10◦ and −8◦ relative to the horizon. Our interpretation allows us to
assign exact dates to the gnomonic lines on the artefact and outlines the
schedule of the merchant ships that sustained the Viking colony in Greenland a
millennium ago.
/Susanne Åkesson
