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How vikings used science, tools to navigate across oceans

How vikings used science, tools to navigate across oceans

(Copenhagen Museum)

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Estimated read time: 6-7 minutes

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SALT LAKE CITY — Humans are, and always have been, a species on the go, our movements motivated by many different things. As hunters and gatherers, it was natural for us to wander large areas in search of food, and sometimes humans were forced to move into a new region after we had outstripped an area’s resources. People also traveled to trade or to raid.

Navigating across land wasn’t too complex because we had landmarks to guide our way. But navigating across oceans, where there are few or no landmarks, required a whole new set of skills and tools.

The Vikings became the world’s greatest explorers from the 8th to the 11th Century. They often made long sea voyages throughout northern Europe and across the Atlantic Ocean using two simple navigational tools — the sun compass and a translucent rock they called a sunstone, according to S. Thirslund in the book, “The Viking Compass.”

The Vikings were Norse explorers, warriors and merchants from Denmark, Norway, Sweden and northern Germany who explored and settled wide areas of Europe, eventually sailing westwards to England, Ireland, Iceland, Greenland and other parts of North America in their famous longships. The word viking is an Old Norse word for "an expedition overseas."

The Vikings became masters of the sea when they became masters of latitude sailing. In a nutshell, latitude sailing is sailing your ship as straight as possible across a line of latitude. If the Vikings were sailing for a known island or point on a distant continent, they would already know the latitude of this destination. All directions given to Viking navigators began with directions and bearings of how to get to the desired latitude, Thirslund said.

Once the navigator had reached the proper latitude, it was simply a matter of keeping the ship on that line and traveling in the direction of their destination until they reached it. It was the Viking’s sun compass that allowed them to become masters of latitude sailing. The sun compass held many similarities to and worked on the same principles as the mariner’s sextant, an instrument that wouldn’t be invented until 1757.

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“The Viking Compass ” explained the sun compass as a primitive inclinometer that was the Viking’s principle instrument for determining their latitude. It was easy to make and easy to use. Its first component is a circular plate, carved from wood or soapstone. The circular plate was known as the sun shadow board. A hole was drilled in the center of the sun shadow board, and a peg was inserted through the hole in the center of the plate. The peg was known as the gnomon.

Thirslund also explained how a viking would use the tools to map an unknown latitude. He said to hold the sun shadow board horizontally. Holding the plate horizontally will cause the gnomon to stand vertically. When the sun hits the gnonom in the center of the plate, it will cast a shadow across the surface of the sun shadow board. On the sun shadow board, mark the edge of the shadow cast by the gnomon. Mark it every hour from sunup till sundown, then inscribe a line connecting the points. It will make hyperbolic curve. This line is known as the gnomon line.

When a Viking navigator wanted to find that same latitude in the future, he kept the tip of the shadow on that line. If the shadow of the gnomon extended past the gnomon line, he knew he was too far north of his desired latitude. If the shadow of the gnomon fell short of the gnomon line, the navigator knew he was too far south, and he would steer his ship to the correct latitude, acording to Thirslund.

Of course, the gnomic line depends on three variables: the navigator’s latitude, the sun’s declination (its height above the celestial equator) and the height of the gnomon.

However, there were difficulties with the vikings' methods, Thirslund said. The sun will be at different heights above the southern horizon at different times of the year. It will be higher during the summer solstice than during the equinox and lower still at the winter solstice, so the shadow that falls across the sun shadow board when the Vikings embarked across the Atlantic in April, would fall shorter across the sun shadow board in June even though the Vikings were still on the same latitude.

In the 1940s and 1950s, flight navigators from Scandinavian Airlines used technology similar to the Viking sunstone to help them navigate across the North Pole. They called their invention the sky compass.

Vikings took the seasonal variances into consideration while navigating and most likely used different length gnomons in their sun shadow boards to compensate for the sun’s varying height, Thirslund wrote.

However, measuring your latitude using such primitive methods on a pitching ship could be a difficult task because to take an accurate reading the sun compass must be kept level. To accomplish this, Thirslund writes, the navigator held the sun compass floating in a tub of water, and the tub held off the surface of the rolling, pitching ship by the crew who held it as steady as they could.

The sun compass, used by a competent navigator, is amazingly efficient, but Norse sailors traveling in the far north latitudes could easily go days, or even weeks, in weather too cloudy to allow the sun to cast a shadow. The Vikings compensated for this with the use of what they called a sunstone.

A Viking sunstone is actually what we now know as cordierite. Cordierite is a crystal composed of magnesium, iron and aluminum that has a unique property that the Vikings found very useful — it can detect the direction from which polarized light is coming.

Light scattered by air molecules is polarized and the direction of polarization is at a right angle to the sun. A cordierite crystal is translucent yellow, but due to its crystalline structure the stone turns a blue and purple color when it is turned at right angles to the sun, even when the sun is obscured by clouds.

The sunstone will still work even if the sun is as far as eight degrees below the horizon. It was this quality that the Vikings found useful because this allowed Vikings to determine which direction they were sailing, according to Thirslund. If a Viking was traveling across the North Atlantic, he would hold up the sunstone in the cloudy light and rotate it until it turned from yellow to purple, and that angle marked the east-west boundary line. They the viking would try to sail on that path.

A Viking navigator using only a sunstone could still easily drift north or south of his desired latitude, but on the next cloudless day by using a sun compass, he could determine his latitude and steer back to his desired course if he had wandered off it.

In the 1940s and 1950s, flight navigators from Scandinavian Airlines used technology similar to the Viking sunstone to help them navigate across the North Pole, according to Oscar Noel and Sue Ann Bowling in the "Alaska Science Forum." They called their invention the sky compass.

Magnetic compasses were unreliable traveling that far north. The modern sky compass is a man-made polarizing filter that works on the same principle as the Viking’s sun compass by determining the direction of polarized light. Sky compasses are no longer used today because they’ve been superseded by gyrocompasses, internal navigation systems, and GPS navigation systems.

The Vikings reached England in 793 A.D., Ireland in 795 A.D., and Greenland (sailing from Iceland) in the 980s A.D. Leif Eriksson, sailing from Greenland, discovered Baffin Island and Labrador (in northeastern Canada) around 1000 A.D.

Steven Law is one of KSL's Outdoors and Recreation editors. He can be contacted at


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