The Uunartoq disc is an artifact discovered in the ruins of a Norse Greenland homestead. It is widely believed to be an early Norse sun compass.
The disappearance of the Norse Greenlanders at some point in the 15th century remains one of the great historical mysteries. In 1948, Danish archaeologist Christen Vebæk was excavating the ruins of the Norse site Ø149 located on the western shore of a fjord known to the Norse as Siglufjord and is today called Uunartoq ("the hot"), a name that denotes both the fjord and the islands at its mouth. One of the islands is the site of geothermal hot springs well known to the Norse and the Inuit and is today a popular destination among tourists.
The ruins at site Ø149 include a church and it is generally accepted to be the colony's Benedictine Convent referenced by Ivar Bardarson, a Norwegian priest who lived in the colony in the mid-14th century as a representative of the Archdiocese of Nidaros and the Norwegian crown. [1]
Among other artifacts, Vebæk discovered a fragment of a wooden disc with triangular notches chip-carved around the perimeter and a hole in the centre. It was fashioned from softwood, likely larch or spruce (some sources indicate oak), [2] and it measured just 7 centimetres wide, 1 centimetre thick and the central hole was 1.7 centimetres in diameter. [3]
Danish marine captain and naval historian Carl V. Sølver examined the notches and deliberate scored lines on the disc and pronounced it to be a sun compass used to determine true north, with the hole in the centre intended for a handle that housed a horizontal directional pin and a vertical pin to cast a shadow. [4] Sølver drew a speculative illustration from which a replica was fashioned, and this explanation was ultimately accepted by Vebæk. [5] The discovery of the artifact prompted increased interest among historians about the possible use of navigational instruments by the Norse, as many experts assumed that they relied solely on non-instrumental resources such as celestial bodies, landmarks or intuition. [6] The magnetic compass does not appear to have been in use in Europe until the early 13th century. [7] While the North Star had become an important navigational tool by the time of Pytheas and regarded as the "Ship-star" by the 10th century, [8] mariners on the open ocean out of sight from any landmark would have had great difficulty in precisely determining true north during daylight hours.
While some scholars continued to argue against the theory of Norse marine instrumentation, [9] the discovery of a similar artifact with gnomonic lines in a Polish archaeological site near Wolin in 2000 has given further credence to the sun compass theory, particularly since the site dates from a period when the Norse had considerable impact in the region. [10]
Like a sundial, a sun compass features a vertical pin. The sun's rays cause the pin to cast a shadow which is longer in the morning and late afternoon and shortest at solar high-noon, and this shadow is used to create gnomonic lines. The disc is placed in a fixed level position and an observer regularly marks the different lengths and positions of the pin's shadow across the disc during the course of the day. When the pin tip shadow marks are connected, the result is a west-to-east gnomonic line that comes closest to the vertical pin at high-noon. In the northern hemisphere, a straight line drawn from the base of the pin to that closest high-noon position will point directly to true north, which will then serve as the compass' north index mark. The gnomonic line will be essentially straight during the vernal and autumnal equinoxes, and downward concave at the summer solstice.
Once these lines have been inscribed on the face of the compass, it can be used during travel. The user holds the device level and rotates it until the pin tip's shadow touches the appropriate seasonal gnomonic line, and the index mark will point to true north.
Sølver noted that the Uunartoq disc appeared to have gnomonic lines consistent with those produced during the summer solstice and the equinoxes (which in 1990 were microscopically shown to be deliberately double traced) [11] and also noted that the disc had 8 triangular dial increments per quadrant, for a total of 32, corresponding with the traditional mariner's compass. In addition to its gnomonic lines, it also had a round dimple on the 9th increment that corresponds with east, where the lines end with the setting of the sun in the west.
In 1984, Norwegian author and explorer Ragnar Thorseth led an international expedition in a replica of a Norse merchant ship, the Saga Siglar. For the passage between Iceland and Greenland, the crew had been given replicas of the Uunartoq disc to test against the ship's modern magnetic compass, and the deviation between the two was described as "negligible" and "...results were far better than the navigators had expected..." [12]
In 2013, researchers from Eötvös University in Hungary argued that the Uunartoq disc could have also been used to determine a traveller's latitude. [13] The researchers pointed to a series of very short inscribed lines stacked atop one another on the disc's north index mark, whereas gnomonic lines by necessity run from west to east across the sun compass's face. Under this theory, the disc's user would have made a reference point at the north index mark at high-noon just prior to departure and then made subsequent high-noon marks during the course of the journey, and compared these against their home's reference point. If the journey's marks were in the same position as the home reference point, it meant that the user had been maintaining a consistent latitude. A high-noon mark coming in below the home reference meant that one was further south (although travellers also would have had to make allowances for the constant seasonal changes of the sun's position at high-noon).
Whether the Norse used these sorts of devices primarily as compasses or latitude readers, both relied on the sun. It is believed that on overcast days, Norse mariners made use of a sun stone, likely clear Iceland Spar (Calcium Calcite) which can be used as a polarization analyzer to find the sun's position through the clouds. [14] There are references to the possible Norse use of sun stones in two Icelandic Sagas; Hrafns saga Sveinbjarnarsonar ("The King looked about and saw no blue sky...then the King took the Sunstone and held it up, and then he saw where the Sun beamed from the stone") and the Saga of St. Olaf ("Olaf grabbed a Sunstone, looked at the sky and saw from where the light came, from which he guessed the position of the invisible Sun"). [15] In addition to their work demonstrating the Uunartoq disc's possible use as a latitude reader, the Eötvös University researchers also argued that if the disc was used with a pair of sun stones, it might have been possible to detect true north up to 50 minutes after sunset, thus serving as a "twilight compass" as well. [16] A 2018 study by different researchers at Eötvös found that "sky-polarimetric Viking navigation is surprisingly successful at spring equinox and summer solstice even in cloudy weather..." [17]
In the History Channel's television series Vikings, a sun compass very similar in appearance to the Uunartoq disc was a significant plot device in the first season, as it allowed the Norsemen to maintain a consistent latitude while sailing west on the open ocean to raid Britain, though it was shown floating in water rather than hand-held as envisioned by Sølver.
Longships were a type of specialised Scandinavian warships that have a long history in Scandinavia, with their existence being archaeologically proven and documented from at least the fourth century BC. Originally invented and used by the Norsemen for commerce, exploration, and warfare during the Viking Age, many of the longship's characteristics were adopted by other cultures, like Anglo-Saxons, and continued to influence shipbuilding for centuries.
A solstice is an event that occurs when the Sun reaches its most northerly or southerly excursion relative to the celestial equator on the celestial sphere. Two solstices occur annually, around June 21 and December 21. In many countries, the seasons of the year are determined by the solstices and the equinoxes.
A sundial is a horological device that tells the time of day when direct sunlight shines by the apparent position of the Sun in the sky. In the narrowest sense of the word, it consists of a flat plate and a gnomon, which casts a shadow onto the dial. As the Sun appears to move through the sky, the shadow aligns with different hour-lines, which are marked on the dial to indicate the time of day. The style is the time-telling edge of the gnomon, though a single point or nodus may be used. The gnomon casts a broad shadow; the shadow of the style shows the time. The gnomon may be a rod, wire, or elaborately decorated metal casting. The style must be parallel to the axis of the Earth's rotation for the sundial to be accurate throughout the year. The style's angle from horizontal is equal to the sundial's geographical latitude.
Viking ships were marine vessels of unique structure, used in Scandinavia from the Viking Age throughout the Middle Ages. The boat-types were quite varied, depending on what the ship was intended for, but they were generally characterized as being slender and flexible boats, with symmetrical ends with true keel. They were clinker built, which is the overlapping of planks riveted together. Some might have had a dragon's head or other circular object protruding from the bow and stern for design, although this is only inferred from historical sources. Viking ships were used both for military purposes and for long-distance trade, exploration and colonization.
Sunrise is the moment when the upper rim of the Sun appears on the horizon in the morning. The term can also refer to the entire process of the solar disk crossing the horizon.
The Norse exploration of North America began in the late 10th century, when Norsemen explored areas of the North Atlantic colonizing Greenland and creating a short term settlement near the northern tip of Newfoundland. This is known now as L'Anse aux Meadows where the remains of buildings were found in 1960 dating to approximately 1,000 years ago. This discovery helped reignite archaeological exploration for the Norse in the North Atlantic. This single settlement, located on the island of Newfoundland and not on the North American mainland, was abruptly abandoned.
Iceland spar, formerly called Iceland crystal and also called optical calcite, is a transparent variety of calcite, or crystallized calcium carbonate, originally brought from Iceland, and used in demonstrating the polarization of light.
A transit of Phobos across the Sun as seen from Mars takes place when Phobos passes directly between the Sun and a point on the surface of Mars, obscuring a large part of the Sun's disc for an observer on Mars. During a transit, Phobos can be seen from Mars as a large black disc rapidly moving across the face of the Sun. At the same time, the shadow (antumbra) of Phobos moves across the Martian surface.
Helluland is the name given to one of the three lands, the others being Vinland and Markland, seen by Bjarni Herjólfsson, encountered by Leif Erikson and further explored by Thorfinn Karlsefni Thórdarson around AD 1000 on the North Atlantic coast of North America. As some writers refer to all land beyond Greenland as Vinland, Helluland is sometimes considered a part of Vinland.
A gnomonic projection, also known as a central projection or rectilinear projection, is a perspective projection of a sphere, with center of projection at the sphere's center, onto any plane not passing through the center, most commonly a tangent plane. Under gnomonic projection every great circle on the sphere is projected to a straight line in the plane. More generally, a gnomonic projection can be taken of any n-dimensional hypersphere onto a hyperplane.
Analemmatic sundials are a type of horizontal sundial that has a vertical gnomon and hour markers positioned in an elliptical pattern. The gnomon is not fixed and must change position daily to accurately indicate time of day. Hence there are no hour lines on the dial and the time of day is read only on the ellipse. As with most sundials, analemmatic sundials mark solar time rather than clock time.
Daytime as observed on Earth is the period of the day during which a given location experiences natural illumination from direct sunlight. Daytime occurs when the Sun appears above the local horizon, that is, anywhere on the globe's hemisphere facing the Sun. In direct sunlight the movement of the sun can be recorded and observed using a sundial that casts a shadow that slowly moves during the day. Other planets and natural satellites that rotate relative to a luminous primary body, such as a local star, also experience daytime, but this article primarily discusses daytime on Earth.
Inuit astronomy is centered around the Qilak, the Inuit name for the celestial sphere and the home for souls of departed people. Inuit beliefs about astronomy are the shaped by the harsh climate in the Arctic and the resulting difficulties of surviving and hunting in the region. The stars were an important tool to track time, seasons, and location, particularly during winter.
Longitude: The True Story of a Lone Genius Who Solved the Greatest Scientific Problem of His Time is a 1995 best-selling book by Dava Sobel about John Harrison, an 18th-century clockmaker who created the first clock (chronometer) sufficiently accurate to be used to determine longitude at sea—an important development in navigation. The book was made into a television series entitled Longitude. In 1998, The Illustrated Longitude was published, supplementing the earlier text with 180 images of characters, events, instruments, maps and publications.
Astronomical rings, also known as Gemma's rings, are an early astronomical instrument. The instrument consists of three rings, representing the celestial equator, declination, and the meridian.
The sunstone is a type of mineral attested in several 13th–14th-century written sources in Iceland, one of which describes its use to locate the Sun in a completely overcast sky. Sunstones are also mentioned in the inventories of several churches and one monastery in 14th–15th-century Iceland and Germany.
Dialing scales are used to lay out the face of a sundial geometrically. They were proposed by Samuel Foster in 1638, and produced by George Serle and Anthony Thompson in 1658 on a ruler. There are two scales: the latitude scale and the hour scale. They can be used to draw all gnomonic dials – and reverse engineer existing dials to discover their original intended location.
A schema for horizontal dials is a set of instructions used to construct horizontal sundials using compass and straightedge construction techniques, which were widely used in Europe from the late fifteenth century to the late nineteenth century. The common horizontal sundial is a geometric projection of an equatorial sundial onto a horizontal plane.
Burt's solar compass or astronomical compass/sun compass is a surveying instrument that makes use of the Sun's direction instead of magnetism. William Austin Burt invented his solar compass in 1835. The solar compass works on the principle that the direction to the Sun at a specified time can be calculated if the position of the observer on the surface of the Earth is known, to a similar precision. The direction can be described in terms of the angle of the Sun relative to the axis of rotation of the planet.
