Simanaitis Says

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MEDIEVAL VIKINGS sailed much of their known world, and even portions of that still unknown, with practical navigation. Yesterday, we learned from an article in The New York Times, April 6, 2018, that these Vikings made use of sunlight polarized as it passed through our atmosphere. Today, we discuss these Viking achievements in more detail by digging into the research papers referenced in The New York Times article.

Going-a-Viking. Image from

The principal source is “Success of sky-polarmetric Viking navigation: revealing the chance Viking sailors could reach Greenland from Norway,” by Dénes Száz and Gábor Horváth, Department of Biological Physics, Eölvös Loránd University, Budapest, Hungary. This paper was published in the Royal Society Open Science journal, April 4, 2018.

Medieval Vikings were a well-traveled lot, over sea and land.

A related 2014 paper, “How could the Viking Sun Compass be used with sunstones before and after sunset? Twilight board as a new Interpretation of the Uunartoq artifact fragment,” is by Balázs Bernáth et al, including Száz and Horváth. Both papers have fascinating and deeply detailed descriptions of medieval navigation. Here are tidbits on several technicalities discussed in these papers as well as a Viking DIY project.

Sunstones are calcite crystals that split polarized light into two beams. By examining the sky through a piece of calcite and noting changes in brightness, one can identify polarization rings around the sun, even in overcast conditions. The researchers say Vikings may have calibrated their crystals in sunny weather, then used them to navigate with occluded sun or even in diminished light just after sunset. Iceland spar is such a crystal; cordierite and tourmaline behave in similar fashion.

Iceland spar is a form of calcite that can be used to identify the sun’s polarization rings, even if the sun is not visible. Image by ArniEin.

Uunartoq is an acceptable Scrabble word, worth 17 points even without double- or triple-letter spaces. It’s also a medieval convent in Greenland where researchers in 1948 discovered a fragment of an 11th-century Viking navigational device.

Admirable ocean-goers though the Vikings were, they navigated without a magnetic compass. Instead, their sun compass used the calibrated shadow of the sun to determine North, in a way akin to a modern sundial.

The Uunartoq fragment, a wooden artifact that functioned as a sun compass—and more. Image from Physics Org.

The Uunartoq artifact is a portion of a 2.75-in.-diameter disc that researchers say was more than just an identifier of North. Combined with sunstones, discs of this type gave Vikings a means of identifying local noon and, thus, determining latitude, the globe’s horizontal demarkations ranging from 0 degrees at the Equator to 90 degrees at the North Pole.

Sunstones and discs employed every few hours on a voyage enabled Vikings to follow East-West routes with some degree of accuracy. Bernáth and his colleagues describe how the Uunartoq artifact functioned as a “twilight” board, a combination of sun compass and identifier of the horizon in low light conditions. They reported that “true North could be appointed… with an error of ±4 degrees” when an artificially occluded sun was just above or below the horizon.

Száz and Horváth, two of Bernáth’s coauthors, took the analysis a step further in the second paper. They ran computer simulations of 1000 voyages between Norway and Greenland, these three-week voyages in randomly varying weather conditions. The theoretical Viking navigator checked his sunstone every three hours (in a northerly summer when extended daylight is the norm).

Above, the researchers’ successful routes from Norway to Greenland in green, unsuccessful ones in red. Below, the the Greenland-Norway return trips. Images from Száz and Horváth.

The researchers reported “surprisingly large success rates” for navigating in overcast conditions, with their theoretical voyages having at least a 92-percent chance of getting within sight of Greenland. Return voyages were even more successful, given the larger acceptable destination.

Viking navigation was not for the faint of heart, nor for the mathematically challenged. Image from Bernáth et al.

DYI Sun Compass. The website describes how to make a Viking sun compass with a nail and a wood board. “To do this instructable properly,” its author notes, “it is not absolutely vital to be wearing a Viking helmet, but it helps.”

This and the following image from

First, hammer the nail through the board. Then calibrate the sun compass with a sunny day, a pencil, and patience: “Spend the day near your sun compass, doing useful things to prepare for your raid (mending sails, sharpening swords, doing careful stretching exercises so you don’t pull a muscle during an important ravish, you know the kind of thing).”

Marking the nail tip’s shadow on the board every 20 minutes and joining the marks yields a “gnomon curve.” The rest is easy: “Find the point where the gnomon curve passes closest to the nail. Draw a straight line from that point to the base of the nail. That will be your North-South line (as a Viking, living in the Northern hemisphere, North is pointing away from the nail.”

Vikings in the Southern Hemisphere, reverse this—and accept that you’re really lost. ds

© Dennis Simanaitis,, 2018

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