Early European sailors used calculations based on the position of the sun to help them find their way around the high seas. While this was probably fairly simple for Mediterranean sailors, it has long been a mystery how Scandinavian seafarers managed to locate the sun’s position given the cloudy and dark conditions at higher latitudes.
However, Icelandic sagas from the time of the Vikings refer to a mysterious ‘sunstone’ used by seafarers for this purpose, which has led scientists and archaeologists to investigate how such a device might have worked and how it might have been constructed. The new research uses stringent experimental tests to show that Iceland spar, a transparent variety of the mineral calcite, could well be the material from which the mysterious ‘sunstone’ was constructed.
The researchers point out that the crystal’s light-polarising properties mean that it can be used to determine the direction of the sun, even under cloudy or twilight conditions. Their results also show that the sun’s position can be calculated within a few degrees of accuracy using this method. While the Vikings left no written records indicating what the sunstone was made of, recent archaeological find provide tantalising hints that Iceland spar might have been used in this way and the researchers urge archaeologists to look out for evidence of the mineral at historical Viking sites.