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How Did the Vikings Navigate Without a Compass?
The Vikings navigated the North Atlantic without a magnetic compass, holding a latitude by the height of the midday sun and the Pole Star, and reading wind, swell, birds, whales, water colour and cloud for the position of land they could not yet see. That answer rests on three kinds of evidence, best kept apart from the outset. The first is textual: sailing directions preserved in the Hauksbók redaction of Landnámabók, the Icelandic Book of Settlements compiled in the thirteenth and fourteenth centuries, and saga episodes such as Bjarni Herjólfsson’s fog-bound drift in the Saga of the Greenlanders. The second is archaeological: a notched wooden half-disc from Uunartoq in Greenland, lead sounding-weights from Viking-Age harbours, and a block of Iceland spar from a wreck four centuries too late to be Norse. The third is experimental: optical and computer studies that test whether the instruments the texts describe could have done the work attributed to them.
The Viking Ship Museum in Roskilde puts the matter with a restraint worth copying: we cannot be sure the Vikings used anything except their senses to find their way (Viking Ship Museum, Instrument navigation in the Viking Age). The sensory methods are attested; the sun compass and the sunstone are plausible, tested in the laboratory, and unproven in the ground.
Every Viking Navigation Tool, and the Evidence for Each
Viking navigators drew on at least eight tools and methods, of which the sensory ones and the lead and line are securely attested, while the sun compass and the sunstone rest on a single ambiguous artefact and a handful of later medieval texts. The distinction between what is attested and what is inferred is the whole discipline of this subject, so the table keeps it in a column of its own.
The Tool Table
Tool, evidence, problem solved, and how far the record lets us trust it.
| Tool or method | Evidence for it | What it solved | How certain we are |
|---|---|---|---|
| Latitude sailing by sun and Pole Star | Hauksbók sailing directions, Hernar to Hvarf; days’ sailing in Landnámabók | Holding an east-west course across open sea | Strong: textual, and the geography works |
| Sun compass (Uunartoq disc) | Wooden half-disc, 7 cm, excavated 1948 at a Norse convent site in Greenland; read as a compass by Carl V. Sølver, 1953 | True north from the sun’s shadow at a known latitude | Contested: Keller and Christensen (2002) read it as a confession-disc |
| Sunstone (sólarsteinn) | Rauðúlfs þáttr, Hrafns saga, church inventories; no Viking-Age find; Alderney calcite from a wreck of 1592 | Locating a sun hidden by cloud or below the horizon | Plausible, unproven: optics shown (2011), voyages simulated (2018), no Norse artefact |
| Sounding lead and pole | Lead weights from Viking-Age harbours; poles on the Bayeux Tapestry | Depth; the approach to shoal water | Strong inshore; unlikely in the deep Atlantic |
| Landmarks and seamarks | Cairns and beacons in place-names such as Vardø; Hauksbók’s instruction to just glimpse Shetland | Coastal pilotage; fixing a departure point | Strong |
| Birds and whales | Hauksbók: birds and whales south of Iceland; Flóki’s ravens in Landnámabók | Detecting land beyond the horizon | Strong as method; the raven story is legend |
| Swell, wind, water colour, cloud | Saga descriptions; ethnographic parallels from Roskilde | Holding a heading under hidden sky; sensing land | Attested in general; hard to test |
| Magnetic compass | No Viking-Age text or find | Not applicable | Not a Viking tool |
What the Table Leaves Open
Two things get conflated here: whether a technique was known, and whether it was used on the open ocean. Lead weights survive from Viking-Age harbours and sounding poles appear on the eleventh-century Bayeux Tapestry, but the Roskilde museum notes that whether these served deep-sea navigation or merely kept ships off the shallows is unclear. The Hauksbók directions treat birds and whales as a waymark south of Iceland, a repeatable observation; the tale of Flóki Vilgerðarson releasing three ravens to find land is legend that may encode the same knowledge in story form. The site’s essay on navigational patterns in birds’ flight is a useful companion.
What Is a Viking Sunstone?
A Viking sunstone, the sólarsteinn of the Icelandic texts, is best understood as a transparent crystal, usually identified as Iceland spar, a calcite whose double refraction lets a trained eye recover the direction of the sun from the polarised light of a clouded sky. The identification is modern. The Danish archaeologist Thorkild Ramskou proposed it in a short 1967 article in the journal Skalk, by analogy with the polarising instruments polar aviators of his day used to find the sun.
Composition and Properties
Iceland spar is a clear, colourless calcite whose defining property is birefringence, or double refraction: a ray of light entering the crystal splits into an ordinary and an extraordinary beam that travel at different speeds and emerge displaced. Two points matter:
- The optical axis: along one direction the two beams coincide, and the relative brightness of the two images depends on the polarisation of the incoming light.
- Availability: optical-grade calcite occurs in Iceland, famously at Helgustaðir in the east, though that deposit is first recorded in 1668 and no source shows the Norse knew it. Cordierite and tourmaline, both dichroic minerals, are the other candidates.
How Polarised Skylight Reveals the Sun
Sunlight scattered by the atmosphere becomes polarised in bands centred on the sun, and the pattern persists through thin cloud and after sunset. The procedure, as reconstructed by Guy Ropars and Albert Le Floch of the University of Rennes and published in the Proceedings of the Royal Society A in 2011, runs so:
- Mark a dot on the upper face of the crystal and look up through it at a patch of sky; two dots appear.
- Turn the crystal until both images are equally bright; the crystal is then aligned with the sky’s polarisation and points toward or away from the sun.
- Repeat on a second patch and take the intersection; the Rennes team reported accuracy near one degree at sunrise and sunset.
The unaided eye can do a coarse version through Haidinger’s brush, a faint figure some observers see in polarised light.
What the Medieval Texts Actually Say
What the period sources actually attest: one narrative and several lists. The narrative is Rauðúlfs þáttr, a short tale attached to the sagas of King Óláfr Haraldsson, in which the king, unable to see the sun in thick snowy weather, has the sólarsteinn fetched, holds it up and sees where light radiates from the stone. Hrafns saga Sveinbjarnarsonar, of the thirteenth century, names a sunstone among prized possessions without describing it; the four versions of Guðmundar saga góða copy that reference; and Icelandic and German church inventories of the fourteenth and fifteenth centuries list sunstones as objects. None is a sailing text, and none is a Viking-Age text. A correction is due. The earlier version of this article, following a widespread claim, credited the Norwegian King’s Mirror (Konungs skuggsjá, written about 1250) with a sunstone passage; a search of the full 1917 English translation by Laurence Marcellus Larson finds none.
The Sun Compass and the Uunartoq Disc
The sun compass is the one Viking navigation instrument with a candidate artefact behind it: a notched wooden half-disc seven centimetres across, excavated in 1948 at a Norse convent site on Uunartoq fjord in south-west Greenland, and read since 1953 as a shadow-compass. The Danish archaeologist Christen Leif Vebæk recovered the fragment from the ruin known as Ø149, a site the fourteenth-century Norwegian priest Ívar Bárðarson described as a Benedictine convent. The Uunartoq disc is about a centimetre thick, of softwood, with a central hole 1.7 centimetres wide, triangular notches chip-carved around its rim and faint incised lines on the face (Archaeology Magazine, 26 March 2014).
Sølver’s Reading and Its Critics
The maritime historian Carl V. Sølver argued in 1953 that the incised lines were gnomonic curves, the daily path traced by the tip of a central pin’s shadow at a fixed latitude, so that a navigator who set the shadow on the curve could read true north from the notches. In a 2002 paper for the collection Vinland Revisited, the archaeologists Christian Keller and Arne Christensen argued that the ambiguity of the original object had been lost on the way, and proposed that the disc was a confession-disc, a mnemonic device by which parish clergy counted parishioners’ confessions (Keller and Christensen, The Uunartoq Bearing Dial). Their conclusion, that the final interpretation has not yet been reached, remains the honest one; a convent floor is not a ship’s deck.
The Budapest Reinterpretations
A Budapest group led by Balázs Bernáth and Gábor Horváth has offered two further readings. In 2013 they proposed that the disc could fix latitude and local noon by comparing the midday shadow against a mark taken at departure; in 2014, in the Proceedings of the Royal Society A, they reinterpreted it as a twilight board which, used with two sunstones and a wooden slab, could recover true north with the sun below the horizon, to within about four degrees. Both show what the object could do, not what it did.
Archaeological and Scientific Evidence: What Has Been Tested
No sunstone has been recovered from a Viking grave, ship or settlement, so the case rests on three tests: the Alderney calcite from a 1592 wreck, the Rennes optical experiments of 2011, and the 36,000 voyages Dénes Száz and Gábor Horváth simulated in 2018. Each answers a different question.
The Alderney Crystal
In 2002 divers on the wreck of an Elizabethan ship lost off Alderney in 1592 recovered a whitish block that Albert Le Floch, Guy Ropars and colleagues identified as Iceland spar. Their 2013 paper in the Proceedings of the Royal Society A showed that calcium-magnesium ion exchange had limited the crystal’s dissolution, and argued it could have served as an optical compass at a time when a ship’s iron cannon could swing a magnetic needle by as much as ninety degrees (Phys.org, 6 March 2013). The Alderney crystal is the only navigational calcite ever found on a ship, and it is four centuries too late to be Norse. The Norse specialist Donna Heddle observed that there is no solid evidence the device was used by Norse navigators, and that the block might have been a magnifier.
The Rennes Experiments
The 2011 Rennes study mounted a calcite crystal in a wooden housing that admitted skylight through a hole and projected the doubled image onto a surface for comparison. Its reported accuracy, about one degree for the sun’s azimuth at sunrise and sunset and a few degrees in dark twilight, is the figure behind every later claim that the sunstone worked. Two cautions belong beside it: the measurement was made on land by physicists who knew what they sought, and calcite, being birefringent rather than dichroic, proved the least accurate of the three candidate minerals in the 2018 simulations.
The 36,000 Simulated Voyages
Száz and Horváth’s 2018 paper in Royal Society Open Science modelled a ship leaving Bergen for Hvarf along the parallel of 60 degrees 21 minutes north, at a constant 11 kilometres per hour over three weeks, under realistic skies, with a navigator who took a sunstone reading at fixed intervals and corrected course (Száz and Horváth, Royal Society Open Science 5, 2018). On the math: with readings every one to three hours, between 92 and 100 percent of voyages sighted Greenland’s mountains; at four-hour intervals success fell to between 32 and 59 percent; at six hours it collapsed to single figures. The authors state that they slightly overestimated success by assuming no storms, no nightly drift and constant coastal visibility. A 2022 follow-up in PLOS ONE by Péter Takács and colleagues found night sailing, reading frequency and sailing date decisive, and weather and mineral choice marginal.
How the Vikings Reached Iceland and Greenland
The Vikings reached Iceland and Greenland by latitude sailing during a summer window, running west along a chosen parallel from a known Norwegian departure point and correcting by landmarks, birds and whales, a method the Hauksbók sailing directions set down in a single paragraph. The logic is geographic before it is instrumental. Bergen lies near 60 degrees north and Hvarf, usually identified with Cape Farewell at Greenland’s southern tip, near 59 degrees 46 minutes; a ship that kept the noon sun at the same height each day would raise the Greenland coast without ever fixing its longitude.
The Sailing Directions
The primary source reads, in the Hauksbók redaction of Landnámabók: from Hernar in Norway sail due west for Hvarf in Greenland, passing north of Shetland so that it can just be glimpsed in clear weather, south of the Faroes so that the sea stands halfway up the mountainsides, and south of Iceland so that birds and whales are seen. The Sturlubók redaction adds the distances: seven days’ sailing west from Stad in Norway to Horn in eastern Iceland, and four days from Snæfellsnes west to Greenland. Neither text mentions a stone or a dial.
Iceland: Naddod, Gardar and the Settlement Layer
Landnámabók credits the sighting of Iceland to Naddod, a Norwegian blown off course on his way to the Faroes, who called it Snowland, and its circumnavigation to the Swede Garðar Svavarsson, who proved it an island, both in the 860s; Flóki Vilgerðarson’s deliberate voyage followed, and permanent settlement under Ingólfr Arnarson is traditionally dated to 874. Ari Þorgilsson (1067-1148), in Íslendingabók, put it at about 870. Archaeology agrees: a volcanic ash fall known as the Landnám tephra, dated to 871 plus or minus two years in the Greenland GRIP ice core, lies immediately beneath the earliest occupation at most Icelandic sites.
Greenland: Erik the Red
Eiríkr Þorvaldsson, Erik the Red, was outlawed from Iceland for killings about 982, spent three seasons exploring the south-western Greenland fjords, and returned about 985 to recruit settlers, naming the country Greenland because, as the saga puts it, a good name would draw people. The fleet sailed in 985 or 986; the saga counts twenty-five ships, of which fourteen arrived. Erik built Brattahlíð on the fjord he named for himself, and the colony grew into the Eastern and Western Settlements. The sources are Eiríks saga rauða and the Saga of the Greenlanders, written some two centuries after the events.
Bjarni Herjólfsson, Vinland and L’Anse aux Meadows
The Saga of the Greenlanders makes Bjarni Herjólfsson the first Norseman to see the American mainland, in 985 or 986, when he sailed from Iceland to join his father in Greenland, lost sight of land after three days, and, in Keneva Kunz’s translation, was beset by winds from the north and fog so that for many days they did not know where they were sailing. When the sun returned he took his bearings and coasted three unknown lands before reaching Greenland; Leif Eiríksson later bought his ship and named them Helluland, Markland and Vinland. At L’Anse aux Meadows, Newfoundland, found by Helge and Anne Stine Ingstad in 1960, three pieces of wood cut with metal blades each carry the radiocarbon spike of the cosmic-ray event of 993 exactly twenty-nine rings inside the bark, fixing their felling to 1021 (Kuitems et al., Nature, 20 October 2021). The fuller story is in the Viking voyages to Vinland, and the disputed coin from Maine in the Maine penny.
Why the Sunstone Still Matters
The sunstone matters less as a proven Viking instrument than as a test case in how a medieval marginal note, a museum-drawer artefact and a laboratory bench can be made to speak to one another without any of them being forced. The popular telling vs the actual record: in film and popular history the sunstone is a crystal compass every Norse skipper carried; in the record it is a word in a fourteenth-century tale about a king, a line in an inventory, and a physics result showing the thing described would have worked.
The claim that the sunstone heads a lineage running to polarising sunglasses or satellite positioning should be set down gently: modern polarimetry descends from nineteenth-century optics. What they did leave is proof that a mental map of latitudes, birds, swells and coastlines could carry a ship of thirty people over a thousand miles of grey water. Whether a crystal helped remains an open question, and I would rather leave it open than close it on a guess; the essay on historical and archaeological mysteries gathers other cases where the same discipline applies.
Frequently Asked Questions
The questions below gather what readers most often ask about Viking navigation and the sunstone, answered from the sources cited above, with uncertain points marked as uncertain rather than smoothed over.
How did the Vikings navigate?
By latitude sailing along a known parallel, using the noon sun and Pole Star, and by reading landmarks, birds, whales, swell, wind and water colour. A sun compass and sunstone are plausible, not proven.
What navigation tools did the Vikings use?
Attested: sun and stars, the lead and line inshore, seamarks, and animal signs. Debated: the Uunartoq sun compass and the calcite sunstone. Absent: the magnetic compass, unknown in the North before the thirteenth century.
Did the Vikings use a sun compass?
Possibly. The only candidate is the seven-centimetre wooden disc from Uunartoq, Greenland, found in 1948 and read as a shadow-compass in 1953; Keller and Christensen argued in 2002 that it was a clerical counting device.
What were Viking sunstones made of?
Usually Iceland spar, a clear calcite with double refraction. Cordierite and tourmaline, both dichroic, are the alternatives and outperformed calcite in the 2018 simulations. No Viking-Age specimen exists to settle it.
How did a sunstone help locate the sun?
Skylight is polarised in bands centred on the sun. A dot marked on calcite appears doubled; turning the crystal until both images are equally bright aligns it with that polarisation and gives the sun’s bearing.
Which sagas and texts mention the sunstone?
Rauðúlfs þáttr gives the one narrative use; Hrafns saga Sveinbjarnarsonar and Guðmundar saga góða name it; fourteenth- and fifteenth-century church inventories list it. The King’s Mirror does not mention it, despite frequent claims otherwise.
Has a Viking sunstone ever been found?
No. The only navigational calcite from any wreck is the Alderney crystal, from an English ship lost in 1592. Norse graves, ships and settlements have yielded none.
What is polarised light, and why does it matter here?
Light scattered by the atmosphere vibrates preferentially in one plane whose direction depends on the sun’s position. A birefringent or dichroic crystal makes that pattern visible when cloud hides the sun.
What have experimental archaeologists and physicists tested?
The Rennes group showed in 2011 that calcite finds the sun’s bearing to about one degree at sunrise and sunset; the Budapest group simulated 36,000 Bergen-to-Greenland voyages in 2018 with high success at frequent readings.
What role did sunstones play in Viking voyages?
If used, they would have supplied the sun’s direction on overcast days so a latitude course could be held; the simulations suggest this alone could bring most ships to Greenland. Whether they were used is not established.
How did Viking methods compare with other navigation of the period?
Mediterranean and Arab seafarers of the period also lacked the magnetic compass, which reached Europe in the twelfth and thirteenth centuries. What set the Norse apart was the open-ocean scale of their latitude sailing.
Did Viking navigation influence modern tools?
Not directly. Modern polarimetry and satellite positioning descend from nineteenth- and twentieth-century physics. The Viking contribution is proof that latitude sailing with sensory cues could sustain Atlantic crossings for centuries.
What is the cultural significance of the sunstone?
In the medieval texts it is a marvel fit for a king and a valuable listed among a church’s goods; in modern telling it has become the emblem of Norse seafaring skill, a role the evidence supports only in part.
Is the Viking sunstone myth or reality?
Both, in separable parts. The physics is real and demonstrated; the medieval word is real and attested; the claim that Viking navigators routinely carried such a crystal at sea remains unproven for want of any artefact.
How does the sunstone bear on present-day science?
It has become a case study in sky-polarimetric navigation: the Budapest group’s papers of 2014, 2018 and 2022 model how well such a method works under real skies, independent of the Norse question.