The Norse Greenland colony was medieval Europe’s most remote outpost. To reach it from the European continent seafarers needed to cross almost 2,000 miles of open ocean. At the time, only the Malays in the Indian Ocean and the Polynesians in the Pacific undertook longer oceanic voyages, but they did so in warmer and more predictable seas. In the Icelandic sagas, Viking seafarers seem to show an almost casual confidence in their ability to make long open sea voyages but in reality Viking navigation was not an exact art. Viking skippers recognised this and whenever they could they hugged the coast, keeping a safe distance offshore to avoid shoals and reefs, and navigating using landmarks on shore. At night, or if bad weather was setting in, they would seek a safe anchorage, rather than risk getting lost or running aground in darkness or poor visibility. Danes and Swedes, who sailed mostly in the North Sea and the Baltic, very rarely had to sail out of sight of land: Norwegians, setting out for Shetland, the Faeroes, Iceland or Greenland had no choice. When they had to make an open sea crossing, Viking navigators used a technique known as latitude sailing. Leaving his home port, the navigator would sail north or south along the coast to reach a point he knew to be on the same latitude as his intended destination. He would then wait until there was a favourable wind blowing in the right direction and head out onto the open sea and try to follow a heading due east or west to his destination.
In European waters, at least, Viking navigators were heirs to a vast body of seafaring lore and sailing directions that had been passed down orally from generation to generation for centuries. Navigation was a specialised occupation and the leiðsagnarmaðr (pilot) might be the only professional seaman on a ship. This did not mean he was the captain: the ship’s owner was always the captain irrespective of how competent a sailor he was. Successful navigators were experts at reading sea and weather conditions, interpreting the movements of wildlife, which could reveal the direction of land, and observing the positions and altitudes of the sun and stars to determine latitude accurately. However, in common with all navigators before the eighteenth century, Vikings had no means of determining their longitude. The best they could do was to estimate their position based on their speed and direction of travel. It is not known how Viking navigators estimated speed, as there is no evidence for use of the ship log before the fifteenth century, but the evidence of the sagas shows that they could do this with tolerable accuracy. In conditions of poor visibility even the most experienced navigators could suffer from hafvilla (‘confusion’), that is completely losing their bearings. This was most likely to happen when a ship was becalmed for a long period in fog, when it could drift imperceptibly far off its course on the ocean currents.
A navigator’s most reliable guide was the Pole Star, which, north of the Tropics, is always above the horizon and always points due north. The Pole Star is also a reliable indicator of latitude. As the still point around which the other stars rotate, the altitude of the Pole Star remains constant all night and, when viewed from any fixed location, remains the same all year round. From night to night a navigator could estimate the height of the Pole Star above the horizon: if it was higher than the previous night, the ship had sailed further north; if it was lower, the ship was further south. In summer in high latitudes the Pole Star could be invisible during the night long twilight. At such times navigators had to rely on the sun, which is due south at noon, for directions. The height of the sun at noon can also be used to determine latitude, though in this case higher means further south, lower means further north. Through observations like these, Norse navigators knew that Cape Farewell in Greenland (59º 46′ N) was almost at the same latitude as Bergen, the main port in western Norway (60º 4′ N). Sailing directions in one copy of Landnámabók advised navigators heading to Greenland to sail a slightly more northerly course, approximately 61º, in order to avoid the Shetland Islands, which share the same latitude as Bergen. A ship from Bergen should first sail north along the coast to Hernar (60º 36′ N), then: ‘sail west but keep far enough north of the Shetlands so that these islands are barely visible in clear weather. One should stay far enough south of the Faeroes so that their steep and high mountains are just halfway up over the horizon. In addition, one should stay far enough south of Iceland so that you can’t see land but just the coast-bound birds. When you reach the east coast of Greenland you should keep a lookout for landmarks and follow the current west around Cape Farewell to the villages on the south-west point.’
The sailing directions do not rely on latitude sailing alone: the navigator is expected to know important landmarks and understand the movements of seabirds. These could provide important clues about the direction of land. During the breeding season (April-August), which was much the same as the Vikings’ sailing season, seabirds feed at sea but return regularly to land to feed their young and to roost at night. Different birds range further to feed than others. Kittiwakes may travel over 100 miles from land to feed, while smaller seabirds such as puffins and guillemots rarely travel more than 6 miles. Observing the flight of seabirds in the morning and evening gives reliable indications of the direction of land. In poor visibility, the presence of puffins and guillemots would also give early warning that land was very close. Some navigators took caged birds with them. When Floki Vilgerdarson set out for Iceland he took three ravens with him. When he released the first, it flew away in the direction of the Faeroe Islands, their last port of call. When he released the second, it circled round for a while before returning to the ship. When he released the third, it flew away straight ahead and by following in that direction Floki found land.
There were many other environmental clues for the navigator who knew how to read them. Whales have regular migration routes and feeding grounds. For instance, there is one south of Iceland, roughly halfway between the Faeroe Islands and Greenland. A build-up of cloud on the horizon may indicate the presence of land. If the sea suddenly slackens in a storm it may be a sign that the ship has sailed into the lee of an island hidden by rain, fog or darkness. The colour and clarity of the sea can provide further clues about a ship’s position. Rivers wash silt into the sea, sometimes clouding it for miles offshore. A seafarer sailing to Greenland would expect to see ice floes when he approached its coast.
Viking navigators were under no illusions about the dangers of seafaring and it is likely that for many the most important navigation aid was a Thor’s hammer amulet, the thunder god Thor being a protector of travellers and seafarers. Compasses or lodestones were unknown to the Vikings but they may have used other simple navigation aids. One of these was the sounding line, which the Vikings are thought to have adopted from the English late in the Viking Age. This was simply a rope with a weight tied on to one end that was lowered from the ship into the sea to measure its depth. It was especially useful in the shallow shoally waters of the Baltic or southern North Sea. English navigators liked to keep about 10 fathoms (60 feet/18.3 m) of water under their keels when coasting.
Vikings may have used two other navigation aids, the so-called sun stone, and a sun compass. The sun stone is mentioned in a small number of saga sources and is supposed to have been a crystal that was used to locate the position of the sun on overcast days. The Story of Rauð and his Sons describes the use of the sun stone on land:
‘The weather was thick and snowy as Sigurd had predicted. Then King Olaf summoned Sigurd and Dagur to him. The king made people look out and nowhere could they see a clear sky. Then he asked Sigurd to tell where the sun was at that time. He gave a clear assertion. Then the king made them bring the sun stone and held it up and saw where light radiated from the stone and thus directly verified Sigurd’ s prediction.’ (trans J. E. Turville-Petre, Viking Society for Northern Research 1947.)
The sun stone is thought to have been the transparent crystalline form of calcium carbonate known as Iceland Spar, which is known for its polarising qualities. However, modern experiments indicate that the polarising effect is not strong enough to locate the sun’s position under a heavy overcast and works only under a clear sky or light overcast when the sun’s position can be seen with the naked eye anyway. No sun stone has ever been found in a Viking context but one has been recovered from an Elizabethan shipwreck off the Channel Island of Alderney, though this does not prove that it was being used for navigation.
The existence of the sun compass rests on even more slender evidence than the sun stone. In 1948, excavations of a Norse monastery at Narsarsuaq on Uunartoq Fjord in Greenland uncovered half of a small wooden disc, around 2¾ inches in diameter (7 cm) with a hole in the centre and equidistant notches cut around the edges. When complete, there were probably thirty-two notches. The surface of the disc is incised with lines, some of which are parabolic. It is these parabolic lines that have led to the disc being interpreted as part of a sun compass. If the disc had at its centre a gnomon, then these parabolic lines might represent the course of the sun’s shadow through the day. These devices are easy to make and would have been a useful aid to latitude sailing. If the course of the sun’s shadow was plotted onto the disc at the port of departure, a ship’s latitude relative to the starting place could easily be determined by measuring the length of the sun’s shadow daily at noon. If the shadow falls short of the line, the shorter shadow shows that the sun is higher in the sky, meaning that the ship has sailed south relative to its starting point. If the shadow crosses the line, the longer shadow shows that the sun is lower in the sky, meaning that the ship has sailed north relative to its starting point. Because the altitude of the sun varies with the time of year as well as with latitude, the device would have been absolutely accurate only on the day it was made and it would have become increasingly unreliable the longer a voyage was, limiting its usefulness. Another limitation is that the compass has to be held absolutely level while a reading is being taken – no easy thing in a small ship on a choppy sea. Floating the compass in a bucket of water might have solved this problem, but only if some way could be found to stop it spinning. The disc may simply have been part of a child’s toy or was perhaps a ‘confession disc’, similar to those used by Icelandic priests to count the number of people taking confession. In any case, the monastery at Narsarsuaq was built after the end of the Viking Age, so even if the disc was part of a sun compass, it is not evidence that they were used by Vikings.
It is possible that by the end of the Viking Age, navigators had access to written tables of astronomical observations. An Icelander called Oddi Helgasson (c. 1070/80–c. 1140/50), whose knowledge of astronomy earned him the nickname Star Oddi, compiled a chart showing the direction of sunrise and sunset through the year from different harbours in Iceland, which enabled navigators to take directions. It is very likely that such knowledge was also transmitted orally, from one generation of navigators to the next.