Sunstone: How the Vikings Used Calcite in Navigation

Vikings have become firmly entrenched in the popular consciousness not only as conquerors and warriors, but also as explorers and conquerors of the seas. It is a well-known fact, although its historicity is still a matter of debate in academic circles, that between the 8th and 11th centuries, Vikings, in between raids and exploration, crossed the Atlantic without the aid of a compass.

Is it worth mentioning that even today, a trip across the Atlantic Ocean is a task that not all yachtsmen dare to undertake? And this is provided that modern navigation devices are available - radars, VHF stations, satellite phones, GPS and AIS. And the Vikings managed to pull off such an undertaking almost a thousand years ago.

The question arises: how was such a grandiose passage possible in the first place? Even today, the North Atlantic does not favor sailors with its sailing conditions. For the Vikings traveling on drakkars, any mistake could be fatal. The expeditions of these seafarers depended on their ability to interpret natural phenomena, navigate by the stars, the Sun, the Moon, and even the waves.

But what should a sailor of the mid-10th century do when the sky is covered with crimson clouds and a squall is about to capsize the wooden boat?

Sunstone

Sunstone is mentioned in Viking legends. This translucent mineral, according to legend, allowed the sun to be seen even in poor visibility. One of the most vivid legends is the story from the Saga of King Olaf, who ruled Norway from 955 to 1030.

An excerpt from the saga states that the king possessed "magic glowing stones" that allowed him to find the sun even on the cloudiest days. Such a description may seem like evidence of witchcraft or fantasy.

This was the view of many researchers until 1967, when the idea of a real use for these stones was put forward. This idea gained popularity, and in the following years, scientific evidence was found that the "sun stone" could indeed be a useful navigational tool.

Not a stone, but a mineral

The majority of researchers believe that the Vikings used a special type of calcite for navigation - Iceland spar. The principle of the crystal's action when searching for a light source (in our case, the Sun) is as follows: the crystal must be raised above you and rotated. The light passing through it will dim if the crystal moves away from the light source, and will intensify when approaching.

The peculiarity of this type of calcite is the double refraction of light, which allows for precise tracking of its brightness. In addition, due to the effect of light polarization, the crystal theoretically helps to determine the position of the Sun even in cloudy conditions. To do this, it was necessary to take "measurements" of light from two different areas of the visible sky.

At first glance, this navigation method seems effective, especially in the North Atlantic, where visibility is often limited. However, it is worth considering that the accuracy of the method is highly dependent on weather conditions and the skills of the observer.

Opinion of the scientific community

Modern research confirms the physical properties of Iceland spar, which in theory could also support its use by the Vikings. The hypothesis about the use of spar is opposed by the fact that until 2013, "sunstones" were not found on the remains of Viking ships. The only known case of Iceland spar being found on a Viking ship was recorded on the Alderney, which dates back to the 16th century. 

However, there is no consensus regarding this discovery in the scientific community - some believe that the mineral could indeed be used for navigation, but as a spare tool, while others do not associate the presence of feldspar with navigation at all. Experiments conducted using calcite did not confirm its full effectiveness, but did not completely exclude this possibility.

In summary, we can draw the following conclusion:

• The hypothesis is correct if we rely on ancient, often semi-mythical texts and the physical properties of Iceland spar.
• The hypothesis is incorrect given the experimental results showing the limited use of the mineral in real conditions.

In the experiments mentioned, the scientists used calcite, cordierite and tourmaline and tested the described properties in practice in different weather conditions. Indeed, with moderate cloudiness, the minerals could be used as an optical instrument, especially calcite, which proved effective with low polarization of light. However, in the harsh conditions of the Atlantic, where there is often increased cloudiness, such use is impossible - there is not enough light.

Today, the idea of using calcite as a navigational tool is seriously questioned, although it is not completely ruled out. Until further material evidence is found, the hypothesis of Iceland spar being used by the Vikings remains interesting but unproven.

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05.12.2024