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An eleventh century artefact, a fragment of a compass dial found at Uunartoq in Greenland, is widely accepted as proof of the ability of Vikings to navigate with sun-compasses. The artefact is half of a wooden compass dial bearing deliberately incised lines that were interpreted as gnomonic lines valid on the day of equinox and near the summer solstice at the 61st latitude. Supposed loose markings of cardinal directions and several unexplained scratches are visible on this find. We offer here a new possible interpretation that some of these scratches might be fundamental lines of a geometrical construction process used for forming the gnomonic lines. Our hypothesis renders the cardinal directions to be precisely marked in the dial and assigns exact dates to both gnomonic lines. We reinterpret the artefact as a combination of sun-compass and sun shadow board designed for appointing local solar noon and the length of the noon shadow at open sea, playing a role analogous to that of a late-mediaeval backstaff. Greenland occurrence of geometrical construction of gnomonic lines, a known cultural asset of ancient European people, may denote that mediaeval Norse people not only shared in European culture, but used its achievements, even in the utmost frontiers.

An alternative interpretation of the Viking sundial artefact: an instrument to determine latitude and local noon