Franck Pettersen: The Viking Sun Compass

Reproduced with permission from the Planetarian, Vol. 22, #1, March 1993. Copyright1993 International Planetarium Society. The Viking Sun Compass or How the Vikings Found their Way Back from New York 1000 Years Ago Franck Pettersen Northern Lights Planetarium Tromsų, Norway (illustrations follow at the end of the article) The saga is the literature and history that tells about the Nordic people-how they lived, where they traveled, and who they killed. The sagas are always written as true stories. In Grųnnlendingesaga, the saga of the Greenlanders, we can read about Eric the Red. He killed a man in Norway, became an outlaw, and fled with his family to Iceland. But he killed another man and became an outlaw there too. He set out west with his ship hoping to find new land, and he did! He was the first European to visit Greenland. He named the place Greenland to entice people follow him. They settled at Brattalid, which translates into "the steep hills;" it was not far from where Julianehåb is today. The Vikings were the first known people to use the keel, which was necessary to keep a stable course when they crossed the oceans. Their sailing route was between the 61st and 62nd degree north on a due western course from Norway to Greenland. We can read their sailing instructions in one of the sagas. In the saga Landnåmabok it says: "From Hernam (near Bergen) in Norway you must hold on to a due western course, and that will take you to Hvarf in Greenland. On your way you will come so close to the Shetland Islands that you can just see them in clear weather. And you will sail so far from the Faroe Islands that you will see half of the hills in the water. And you will be so close to Iceland that you will see whales and birds from there." Viking Navigation Navigation before the Vikings was coastal, so how did the Vikings manage to keep their straight course across this great distance? One of the theories is that they used Icelandic feldspar (Iceland Spar?) to find the general direction. You can use it as a polarization filter to find the area of the sky 90 degrees from the sun. This theory only holds water if you can accept a navigation with an error of plus or minus 30 degrees from the set course. Another theory is that the Vikings knew the magnetic compass. They might have, but even that is a problem because the deviation ever changes during the voyage. What about the stars? Didn't the Vikings know about star navigation? North of the Arctic Circle there is continuous daylight for months in the summer. And even at 62 degrees north, there are very few stars in the middle of the summer. And the Vikings voyaged as a summer occupation. Did They Reach New York? Were they there, at the North American continent? There is absolutely no doubt that they were, but the only place where archeological evidence is found is at L“Anse aux Meadows at northern Newfoundland, Canada. When I look at the question "how far south did they go?" I approach this from three different angles. Compare with the other adventurous Viking voyages and the social pressure on the Viking captain. What are the geographical descriptions in the saga. What are the important pieces of astronomical information from the Vinland Saga. Vikings before Lief Eriksson went from Norway through Gibraltar and all the way to the eastern Mediterranean. Vikings had crossed the Atlantic Ocean and settled at Iceland and Greenland. We also know that they crossed the much shorter distance over to the American continent. The Vikings in Iceland, Greenland and Newfoundland knew about these voyages. There is no reason to believe that they stopped at Newfoundland, but rather that they went much further south. The distance from Newfoundland to New York is only one fifth of the distance they sailed in Europe. Having reached Newfoundland, there was a pressure on the next Viking captain or Viking chief to go further south to explore new lands to prove that he was a man, and that he was a skilled navigator and explorer. In the saga we read that Bjarne Herjulfsson in the year 986, on his way to Greenland, went into fog and lost his direction. They turned south, sailing for two weeks with land on the port side of the ship before reaching the latitude of southern Greenland. Years later in Norway, Bjarne had to suffer a lot of teasing for being a coward because he did not go ashore in this new land. But in the year 999 Leif Eriksson was the one to continue. And he wanted to be sure that he went further south than Bjarne did. Quite a few things surprised Leif and his men in this new land. The most important to us are: The whole winter went by without temperatures below the freezing point, and without snow. They found wild grain. There was hardly no brown grass, even in the middle of the winter. They found wild grapes. One of Leif's men was originally from Germany. One day he was missing, and when they found him again, his face was red, they did not understand him when he talked, his eyes were rolling, and he did funny things with his face as he talked. The explanation was that he had found grapes, and he knew from Germany how to make wine of them. Leif named the land Vinland the Good. Astronomical Observations The astronomical observation mentioned in the Vinland saga is as follows. At skamdagr, the shortest day of the year, Leif observed the sun to be in Eyktarstad and Dagmålsstad. Eykt, or in modern Norwegian ųkt, means a period of work. Eyktarstad means that Leif had seen the sun in the direction on the horizon where work was to finish in the afternoon according to the tradition in Norway. In modern language he observed the sun above the horizon 60° west of south at 4 o'clock in the afternoon. Eykt at sea is still today 4 o'clock. The saga does not say set in eyktarstad, so it is to be understood "had not set in eyktarstad." The most radical interpretation of the information from the saga gives us a northernmost possible latitude of 37° north for Leif“s winter camp. Chesapeake Bay in Virginia is in this area. The distance from Greenland to Chesapeake Bay is the same as from Bergen in Norway to Gibraltar. The calculations can be done in spherical astronomy, and they are not very complicated, but it is very well suited for presentation with a planetarium projector as a part of a program. If we instead of the most radical interpretation of the observation use the most conservative, we will still find Leif“s camp at 42° north. Other captains followed: Leif's brother Torvald, a captain called Torfinn Karlsevne and Leif“s sister, Frųydis, who was the leader of the last of these expeditions. We know this about the last expedition: Because of the favorable winds, they had such a fast journey back to Greenland that it is specially mentioned in the saga. Early in the spring the ships were made ready, and they were back already early in the summer. These ships made 6 - 8 knots under good conditions. How did they find their way back from New York? We have to keep in mind that most of their navigation was coastal navigation. It took place in the summer, and preferably around summer solstice. In the case of ocean navigation, they sailed on a course due west or due east along latitude 62° north. To manage this, they did navigate by star, the star-the sun. Two simple but amazingly accurate devices helped them with that. The first one was a "solskuggefjųl" - a sun shadow board. This was a circular board with a tip in the middle, and the board was allowed to float in a bucket of water. Concentric circles represented different dates. When the shadow of the tip was observed around noon it was supposed to reach the circumference of the right circle, and they knew they were on the right latitude. Another possibility was to move the tip in the middle up and down according to different dates. The Sun Compass The other instrument was the real amazing one: The sun compass. This instrument draws on the fact that the sun“s shadow from the tip in the middle of a disk describes different hyperbolas at different times of the year. When you have the hyperbola representing 62° and the four weeks around summer solstice, you don“t have to know the time of the day in order to find the general directions. All you have to do is rotate the disk until the shadow of the tip falls on the hyperbola, and the general directions are given with an accuracy of a few degrees. One of the ingenious things about navigating with this instrument is that if you should choose the wrong gnomon curve and get a course that is a little too much north in the morning, this will be corrected in the afternoon by a slightly south bound course-and your average direction will be correct. The only archeological evidence for this Viking compass was found in Greenland by the archeologist C. L. Vebęk of Denmark. Later it was interpreted by Captain Sųlver and by Sųren Thirslund at the Nautical Museum at Kronborg Castle and by professor Curt Roslund at the University of Gųteborg. The Viking compass that was found had different hyperbolas or gnomon curves, and the north direction is clearly marked with 16 small cuts crossing a long line. If we count the spikes from north and to the right we have 90° or due west, at spike number 8. This also indicates that dividing the compass into 32 directions was done already by the Vikings, before the magnetic compass was in use in Europe. References: Almar Nęss: Hvor lå Vinland, Dreyers Forlag, Oslo 1954. S. Thirslund & C. L. Vebęk: The Viking Compass, Handels og Sųfartsmuseet på Kronborg 1992, ISBN 87-981869-8-1. Kåre Prydtz: Lykkelige Vinland, Aschehoug, Oslo 1975. ISBN 82-03-06540-6. Saga: Flateyabok Saga: Landnįmabok The Viking Compass can be ordered from the Danish Maritime Museum, Kronborg Castle, 3000 Helsingųr, Denmark. This article was originally presented as a paper at the IPS Conference in Utah in 1992.
The bearing-dial from Uunartoq Fjord placed in a compass-card of today, divided into both compass points and 360 degrees. The straight line passing through 82 degrees and 278 derees in the modern compass card is the line followed by the sun's shadow at the equinoxes, also marked on the find. If the notch number 13A was removed deliberately, the division of the bearing-dial is correct within 15 degrees.
Compass card with accessories which was sent with the yachtsmen competing in the two great races Round Zealand and Round Fynen. They were made to be placed on top of a beer bottle, which should be held with two fingers near the top.
The solskuggerfjol (sun shadow board) mentioned in the History of the Faroe Islands, was used for determining latitude. It was a circular wooden board about 250 to 300 millimeters in diameter. In the center was a gnomon, the height of which could be set to the time of the year. To keep it level, the board was placed in a bowl of water. The shadow of the noon sun was observed. A circle on the board gave the line the shadow should reach if the ship was on the desired latitude. If the shadow was beyond the line the ship was north of this latitude; if inside, the ship was south of it.
Reproduced with permission from the Planetarian, Vol. 22, #1, March 1993. Copyright1993 International Planetarium Society.
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