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date: 26 July 2021

Sun, Moon and Planets in Medieval European Folk Traditionfree

Sun, Moon and Planets in Medieval European Folk Traditionfree

  • Þorsteinn VilhjálmssonÞorsteinn VilhjálmssonPhysics Department, Science Institute, University of Iceland


The subject of astronomy in folk tradition, or folk astronomy, requires some explication. It is, for instance, not the same as ethnoastronomy, which primarily studies the astronomical ideas of contemporary societies. However, the subject overlaps with archaeoastronomy when defined widely as the interdisciplinary study of prehistoric, ancient, and traditional astronomies worldwide within their cultural context that includes both written and archaeological records.

The most useful definition of “astronomy in folk tradition” might be “astronomy of the people or of the common man,” or even “lay astronomy,” left to us through tradition, where the term “astronomy” may, for further clarity, be replaced by “ideas and observations of the sky.” In any case, it is worth keeping in mind that the content of folk astronomy of one society may overlap with the content of established astronomy of another society at another time and place. Scientific ideas or theories have their roots in the past, even before the advent of any “experts.”

Folk astronomy of the past is often less accessible for historical studies than mainstream astronomy, especially in a society leaving few records or artifacts. Revealing sources may, however, be found by looking beyond the conventional. For instance, various sources on mythology and religion may give information on the astronomical and cosmological ideas of previous societies. Purportedly fictional literature, like the works of Dante and Chaucer, may also yield information of this kind, although they were not explicitly composed for that purpose.

But there are also writers who have deliberately written on the astronomical ideas of their society at their time, although their works were outside of the best known corpus and sometimes intended for common people. Two Old Norse examples are the 13th-century Norwegian King’s Mirror and the Icelandic 12th- to 14th-century material edited in the volume of Alfræði íslenzk II. Among other things, these sources treat phenomena that are not observable outside the subarctic region. A third example is the 14th–15th century North European Seebuch with practical information for seamen, partly linked to astronomy.

In any case, two types of folk astronomy can be distinguished: (a) practical astronomy that people use as a tool in daily life, for example, to determine the time of day or year, or for travel and navigation; (b) ideas related to cosmology or cosmogony, religion, or supernatural beliefs, which would neither imply practical uses nor consequences.


  • History of Ideas about Planets and Planetary Systems

Introductory Remarks

Many of the written sources for the folk tradition of medieval European astronomy will probably not be known to the reader. Therefore, the article starts with a survey of sources. Most of the sources used here come from Northern and Western Europe. They can be taken as a kind of representatives for the whole of Europe, giving a general sense of the kind of knowledge that may have existed in other European societies in the Middle Ages.1

Besides other more conventional sources, the article discusses the astronomy found in the writings of Dante and Chaucer, the medieval literary giants who shared a thorough knowledge of the astronomy of their time and used it even in their most known fictional works.

After a treatment of the sources as such, their content is discussed further, including mythology, cosmogony, cosmology, and astronomy, with a touch of geography and navigation. As a representative of mythology, a subsection is devoted to the Eddas, whose roots and influence can be traced over most of Northern Europe, roughly speaking at least down to the Alps, see, for instance, Figure 1. The article then discusses ideas on the shape of the Earth and the various cycles of sun and moon that were of special concern to people in medieval Europe. In several cases it appears that the people behind the North European writings were not totally reliant on the message of the Church or early medieval scholars, but stood by their own observations in cases of disagreement.

Certain threads in the material on celestial cycles lead to the subject of celestial navigation, which started in Northern Europe in the 8th century or so and was a part of the technological basis for the discovery, exploration, and settlement of the more distant North Atlantic islands. The final subsection contains a brief discussion on the relation between the planets and the weekday names in Romance and Germanic languages.

The Sources

Although most of the available sources on medieval European folk astronomy are North European, it does not at all imply that there was no astronomy elsewhere on the continent. Thus, there are all kinds of archaeoastronomical relics all over Europe from the last several millennia, for instance the famous Stonehenge monument from the 4th millennium bce. Admittedly, it may not be trivial to call them medieval, because they derive from a Neolithic or prehistoric society rather than a really medieval one. And the reader should not forget the principle that absence of evidence is not the same as evidence of absence. Many of the ideas and activities treated in the article have certainly been known and practiced in the more southern or more eastern parts of Europe. The Northern items discussed here may thus be taken as pars pro toto, representatives of ideas and activities that were more widespread than meets the eye.

Figure 1. Halley’s Comet on the Bayeux Tapestry. The tapestry describes the series of events leading to the battle of Hastings in 1066. It is a marvelous source on life and work in Northwestern Europe at the time. This figure shows the comet of 1066 as a portent of defeat, following the coronation of King Harold Godwinsson, who lost his life some months later in the battle. The artists ignored the fact, by poetic license, that the comet arrived after the battle. (Creative Commons).

The Eddas

The Eddic poems (Eddukvæði) are the earliest written primary source considered here. They were composed in oral form during centuries, until the bulk of them was deposited on Icelandic vellum in Old Norse in the 13th and 14th centuries (Kristjánsson & Ólason, 2014, pp. 40–55; Sigurðsson, 1998, pp. xi–xxiii). The most important of the manuscripts is the Konungsbók (King’s Book, Codex regius) from around 1270. Some of the poems were sufficiently known around 1200 to be referred to by the Danish scholar Saxo Grammaticus (c. 1160–c. 1220) (see the subsection “Adam and Saxo).”

A part of the Eddic poems, called poems of gods (goðakvæði), reports on the æsir, the gods of Northern Europe in this period; and another part, the poems of heroes (hetjukvæði), describes various more or less historic medieval kings and princes in Europe. The area of origin and influence of these poems, in terms of subject matter and composition, both for gods and heroes, does not only comprise Scandinavia, including Iceland, but also Germanic-speaking areas further south. There is a critical edition of the Eddic poems, by Kristjánsson and Ólason (2014). Out of several English translations, the one by Carolyne Larrington (1999) is used here.

Apart from the Eddic poems, there is also the Prose Edda or Snorri’s Edda (Snorra Edda), written soon after 1220 by the Icelandic author Snorri Sturluson (1179–1241). It is based on the Eddic poems and other sources, some of them otherwise unknown, and it adds considerably to our knowledge of Old Norse mythology. There is a recent philological edition by Anthony Faulkes in the original Old Norse, with notes and glossary (Sturluson, 2005). An English translation is also available by Faulkes (Sturluson, 1995).

Adam and Saxo

Adam of Bremen (before 1050–1081/1085) was a medieval scholar based in Bremen and Hamburg. He is best known for his chronicle Gesta Hammaburgensis Ecclesiae Pontificum (Deeds of Bishops of the Hamburg Church; Adam, 2002). He worked with Archbishop Adalbert of Hamburg (c. 1000–1072) from 1066 or 1067 to Adalbert’s death. He was in a good position to study the history and geography of the present Northern Germany, and a stay at the Danish court allowed him to make similar studies of Denmark and the other Scandinavian countries. His work is an important source on the early history of the region and has been translated, for example, to English, Danish, Swedish, and Norwegian.

The Gesta falls into four parts, of which the fourth is most valuable here. It gives a description of Denmark; Sweden; Norway; the Orkneys; Thule, which is “now called Iceland” and is “the farthest island of all” (Adam, 2002, p. 216); Greenland; and Halogaland, that is, northernmost Norway. Finally, the Danish king Sven told Adam about Vínland (Wineland) which was an area on the North American coast, discovered by the Old Norse around year 1000. Adam was the first to mention it in European texts:

He [King Sven] spoke also of yet another island of the many found in that ocean. It is called Vinland because vines producing excellent wine grow wild there. That unsown crops also abound on that island we have ascertained not from fabulous reports but from the trustworthy relation of the Danes. Beyond that island, he said, no habitable land is found in that ocean, but every place beyond it is full of impenetrable ice and intense darkness.

(Adam, 2002, chap. 39, p. 219)

Adam’s Gesta provide a part of a bridge between the Nordic countries and the rest of Europe, strengthening the message of interaction already mentioned for the Eddas. His ideas appear again in the subsections “Shape of the Earth” and “Cycles of the Tides.”

Saxo Grammaticus (c. 1160–c. 1220) was a Danish scholar, thought to have been an assistant to Absalon, archbishop of Lund (then Danish but now in Sweden). His Gesta Danorum (The History of the Danes;Saxo, 1979), a history of Danish kings and the Danes in general, was written with the explicit purpose of “glorifying our fatherland” (Saxo, 1979, p. 4). His sources and his text were not all completely historical in the modern sense, drawing on many kinds of data like tales of the Icelanders, which he praises; ancient books; rock inscriptions; and statements by Absalon on his own time.

For this article, the most interesting thread in the Gesta is that of mythology and early history where Saxo uses the Eddic poems described in the section on them. That is the earliest written reference to them and hence a significant contribution to our ideas on their provenance.

Sagas of Icelanders and Related Literature

Most of Icelandic medieval literature is written in the vernacular, that is, in Old Norse, then more or less the common language of Iceland, Norway, Sweden, Denmark, Faroes, Orkneys, and Shetland. Old Norse is still readable for many Icelanders. The literature consists of many branches, among them the Eddas, the Icelandic family sagas and the encyclopedic writings.

The Sagas of Icelanders (Íslendingasögur, also known as Family Sagas) are a unique genre of literature. Most of them report on Icelanders and are set in the period from the settlement around 870 ce up to the 11th century. They describe people’s daily life, families, feuds, and adventures at home or abroad. The style is concise and sensible, and the character descriptions are convincing and memorable. Not the least, compared to many other genres of the time, the sagas are secular and down to earth in that the role of supernatural phenomena is minimal. On the contrary, they often demonstrate keen observations and fairly good knowledge of natural phenomena.

The oldest extant manuscripts of each saga are normally on vellum, from the 13th14th centuries, but the content has often been transmitted in oral or written form for some time before that, and only a few sagas have been tentatively attributed to a single author. Scholars have for a long time been at loggerheads on the question of “fact or fiction” in them—history or Schönlitteratur—but it can be safely said that they display the general views and mentality of medieval Icelanders and their neighbors, from the alleged time of report up to that of final composition and writing. The sagas touch many kinds of knowledge and activity, including astronomy, navigation, geography, and exploration.—This description also holds more or less for other related but less extensive genres like for instance Heimskringla (sagas of kings), Sturlunga saga, and Biskupa sögur (biographies of bishops).

There are numerous editions of the sagas in the original language. The most important critical ones are often found in the series Íslensk fornrit (Icelandic Medieval Writings; see, e.g., Benediktsson, 1968; Kristjánsson & Ólason, 2014; Sveinsson & Þórðarson, 1935; Vilmundarson & Vilhjálmsson, 1991). There are also many translations to other languages. For English, the most recent comprehensive edition is that of Hreinsson (1997).

Encyclopedic Writings

Most of the medieval encyclopedic literature of Iceland relating to astronomy and calendar is found in a handful of vellum manuscripts from the 12th14th centuries. This material has been collected in a high quality semi-diplomatic eclectic edition by two philologists, the Swedish Nathanael Beckman (1868–1946) and the Danish Kristian Kålund (1844–1919). It appeared in 1914–1916 with the title Alfræði íslenzk II: Rímtöl (Icelandic Encyclopedia II: Time Reckoning; Beckman & Kålund, 1914–1916). Kålund took care of the textual aspects, spelling, variants, and so on, and wrote an introduction on the manuscripts, and Beckman wrote the critical notes and a thorough introduction on the content. Because Beckman was well versed in astronomy and its history, this edition has left its mark not only in philology but also in the history of science and ideas.

Most of the astronomy texts in Alfræði II clearly derive from standard European sources like Martianus, Macrobius, Isidore, and Bede, and even Sacrobosco in the case of the younger manuscripts. But there are scattered remarks or inserts that are clearly of indigenous origin, suggesting observant and critical authors, referring to their own environment and preferring to believe their own eyes when their observations did not fit in with the papal authorities. Examples of this are found in most of the subsections of the section “On Heaven and Earth.”

The Norwegian King’s Mirror

The King’s Mirror (Konungs skuggsjá; Holm-Olsen, 1983) was written in southern Norway, presumably in 1250–1260, in an environment close to the royal court. Its oldest fairly complete manuscript is written in Old Norwegian, which was already a little different from Icelandic, but important Icelandic manuscripts also exist. The first section of the work is a kind of a manual for seafaring merchants and is the most relevant one for this article, containing practical information on astronomy and navigation, partly derived from earlier medieval European scholars but partly also from local observations, for instance, of solar motion in the arctic and subarctic north; see the subsection “Lunar Cycle.”

The King’s Mirror has so far not been closely studied by scholars with knowledge of astronomy and related matters, and the English translation by Laurence M. Larson (1917) is unfortunately deficient regarding astronomy. The translation to French by Einar Már Jónsson (1997) is better in that respect.

The edition by Ludvig Holm-Olsen from 1983 is a diplomatic, single manuscript, showing the text of the “main manuscript,” AM 243 bα‎ fol., and of another Norwegian one for its lacunas, followed by a sparse selection of variants at the back. Holm-Olsen has also published a thorough study of the manuscripts of the work (1952) and edited a facsimile edition of the main Icelandic manuscript, AM 243 a fol., which contains far more of the astronomy than the Norwegian main manuscript bα‎ (1987).

Dante and Chaucer

The Florentine poet Dante Alighieri (1265–1321) is one of the giants in the history of ideas. He started his career as a politician but was later exiled, and switched to self-education and writing. His works show an incredibly broad erudition, covering astronomy among many other fields. His most famous work is Divina Comedia (Divine Comedy). It was and is very influential in many respects; for example, it served to define and develop Italian as a literary language instead of Latin, thus paving the way for Galileo’s writings, among others. This encouraged a similar development in other European languages in the sequel. There is a recent highly readable English translation of Divine Comedy in verse by Robin Kirkpatrick (Dante, 2012).

Dante weaves much of the Ptolemaic astronomy of the time into his work. He apprehends the sphericity of the Earth, although he has his own ideas on the content of the Southern Hemisphere (see the subsection “Shape of the Earth.” He uses the positions of the planets and the fixed stars frequently for timing events (e.g., Purgatorio, Canto 25, beginning), and he follows the Heraclidean order of the seven planets in the journey from the top of the Purgatory to the highest heaven (Dante, 2012, Paradiso, passim) (see the subsection “Weekday Names”). Some of his astronomical references may not agree completely with fact, but his main concern may have been that of showing what can be done with astronomy (Figure 2). The interested reader may enjoy a treatment of Dante‘s astronomy by the late British historian of astronomy John North (1994, pp. 230–232). Orr’s book is also very useful for grasping Dante’s astronomy (1956).

Figure 2. Dante’s scheme of the universe.

(Adapted from Michelangelo Caetani, Duca di Sermoneta, 1921; from

It is interesting that a man like Dante had all this astronomical knowledge and felt motivated to incorporate it in his influential masterpiece. Another thing to note is that he somehow must have thought that his readers would enjoy it and be able to relate to it. In this way, the Divine Comedy can be seen as a kind of a textbook of astronomy for the general reader, encouraging people to study and understand this important field.

Geoffrey Chaucer (1343–1400) was one of the major writers of the English Middle Ages, but his main job was that of a civil servant and diplomat. His most famous work is The Canterbury Tales, a collection of partly connected short stories in verse form, written in Middle English, the vernacular of the time (Chaucer, 1996; n.d.). He was well educated and earned a reputation as a philosopher and astronomer. He even composed A Treatise on the Astrolabe for his son (Chaucer, 1870). Like Dante, he was a pioneer of the vernacular and was influential in disseminating knowledge of astronomy. He often traveled abroad, especially to present Italy. He knew Dante’s work and referred to him with admiration in many places (e.g., Chaucer, 1996, “Monk’s Tale,” lines 3257–3259). His remains are in the Poets’ Corner of Westminster Abbey (Chaucer, 1996, pp. viii–xiii). There is a very readable translation of the Tales to Modern English by Nevill Coghill (Chaucer, 2003).

The Canterbury Tales abound with references to astronomy and astrology, for instance, in timing of events, persons using the astrolabe, and reports on the influence of the planets on decisive events. Examples of this kind are found in the subsections “Daily Solar Cycle” and “Cycles of the Tides.”

Das Seebuch

Das Seebuch (The Book of the Sea) is a handbook in Low German for West European navigators, treating the coastal waters from the western Mediterranean to the Baltic, including most of the British Isles but omitting Western Norway. It is written by several authors, preserved mainly in two manuscripts, and the content is in three layers. The most recent part is dated to around 1470, but the earliest content may be up to 150 years older (Sauer, 1996, pp. 16, 40, 63, 220–221). It describes tides and currents (Sections I–IV), and various other features of the coast and the coastal seas, like sailing distances and other sailing directions. Several aspects of Das Seebuch are of special interest here, for instance, the treatment of the tides, the use of celestial bodies for orientation and for finding latitude, and the consequences of Earth’s sphericity for sightings at sea. These subjects are discussed further in appropriate subsections of the article.

There is a diplomatic edition of the work in the original language by the German historian Karl Koppmann (1839–1905), showing the texts of the two main manuscripts separately and containing a useful glossary (Koppmann, 1876). A thorough scholarly treatment of the content of the Seebuch is given in a book by the German nautical historian Albrecht Sauer (1996). It is in Modern German with summaries in English, French, and Russian.

On Heaven and Earth

After the treatment of sources above, this article now turns to astronomical themes in the Medieval European tradition. The oldest theme is that of mythology and stars, followed by the shape of the Earth. The daily and the annual solar cycles were also of interest for the Europeans of this period. Parts of Europe also have conspicuous ocean tides related to the lunar cycle, receiving considerable attention in the sources. Finally, celestial navigation and the weekday names are discussed.

Mythology and the Stars

The first Eddic poem in the Codex Regius is the Völuspá (literally Prophecy of the Seeress). It contains a conversation between the seeress (völva) and the chief god Óðinn, whose name appears in the English “Wednesday” and the Nordic Onsdag. The seeress describes several subjects of cosmogony and cosmology, along with old stories on the dealings of the gods with humans, giants, dwarfs, and so on. The giants were the first beings in the world, without any further explanation, and one of them, Ymir, is involved in a kind of Genesis:

Early in time Ymir made his settlement, there was no sand nor sea nor cool waves; earth was nowhere nor the sky above, a void of yawning chaos, grass was there nowhere. . . . From the south, Sun, companion of the moon, threw her right hand round the sky’s edge; Sun did not know where she had her hall, the stars did not know where they had their stations, the moon did not know what might he had. (Larrington, 1999, 4, verses 3 and 5)

According to the second verse, the moon was initially ignorant of its powers, for instance of lighting up the night and governing the tides (Kristjánsson & Ólason, 2014, p. 292). The reader may also infer from this that the sun, moon, and stars are here seen as some kind of conscious beings created by the gods and belonging to their world. As to the five wandering planets they do not have any major role in mythology or cosmology of this literature, partly because of their limited visibility in the Arctic and Subarctic see MacDonald (2018).

Then all the Powers went to the thrones of fate, the sacrosanct gods, and considered this: to night and her children they gave names, morning they named and midday, afternoon and evening, to reckon up in years. (Larrington, 1999, p. 4, verse 6)

They gave names to the mid-morning (miður morgunn; 6 a.m), noon (“midday,” miður dagur), undorn or nón (3 a.m), and mid-evening (miðaftann; 6 p.m). These terms are discussed further in the subsection “Daily Solar Cycle.”

These quotes show the emphasis placed on the moon in Old Norse ideas of the sky and celestial bodies. Somewhat later, the first human beings, Askr and Embla, enter the scene, and the gods give them “breath …, spirit …, blood … and fresh complexions” (Larrington, 1999, p. 6, verse 18). A large tree was also an important part of the cosmology:

An ash I know that stands, Yggdrasill it’s called, a tall tree, drenched with shining loam; from there come the dews which fall in the valley, green, it stands always over Urd’s well. (Larrington 1999, p. 6, verse 19)

The “shining loam” (hvítur aur) might be a murky and fertile water from a well (Kristjánsson & Ólason, 2014, p. 295).

The world later comes to an end, called Ragnarök, with a lot of fighting and destruction. The sun turns black for some time, and the stars vanish; the Earth sinks into the sea but rises again, although the very end is ambiguous on that, because the seeress then “sinks down” (Larrington, 1999, pp. 11–12, verses 54–62).

The Völuspá is followed by the poem Hávamál (“Sayings of the High One”; Larrington, 1999, pp. 13–35), containing all kinds of wisdom on daily life in the Old Norse world. This is followed by more poems of gods and then the poems of heroes that report on various early medieval heroes of Northern Europe, overlapping, for instance, with Wagner’s Ring des Nibelungen. Direct statements on matters astronomical are not found in these poems, but they are another example of a bridge between the Old Norse world and the more southerly parts of Europe, like present-day Germany.

The Prose Edda also has material on astronomy and related matters, partly overlapping with that of the Poems. Its prologue contains the following perceptive text:

One of the earth’s characteristics was that when it was dug into on high mountain tops, water sprang up there and there was no need to dig further for water there than in deep valleys. It is the same with animals and birds, that it is just as far to blood in the head as in the feet. It is a second property of the earth that every year there grows on the earth vegetation and flowers and the same year it all falls and fades. It is the same with animal and birds, that their hair and feathers grow and fall off every year. . . .

Similarly they learned from their elderly relatives that after many hundreds of years . . . there was the same earth, sun and heavenly bodies. But the courses of the heavenly bodies were various, some had a longer course and some shorter. From such things they thought it likely that there must be some controller of the heavenly bodies who must be regulating their courses in accordance with his will and he must be very powerful and mighty; and they assumed, if he ruled over the elements, that he must have existed before the heavenly bodies; and they realized that ... he must rule the shining of the sun and the dew of the sky and the produce of the earth which is dependent on it, and similarly the wind of the sky and with it the storm of the sea. . . .

But so as to be better able to give an account of this and fix it in memory, they then gave a name among themselves to everything, and this religion has changed in many ways as nations became distinct and languages branched.

(Sturluson, 1995, pp. 1–2, 2005, pp. 3–5)

The reader may compare the content of this subsection with religious creation stories from other societies, for example, in other articles at this website.

The Shape of the Earth

Historians of science will know that for most astronomers and philosophers from the 4th century bce onward the Earth was spherical (Kuhn, 1957, p. 27). Other ideas, though, were clearly on offer for a long time for people who ignored, for instance, Ptolemy’s seminal Almagest of the 2nd century ce (Ptolemy, 1988, see Figure 3) or were not in a position to observe the otherwise clear-cut signs of sphericity.

Figure 3. Ptolemy’s inhabited world. The map is made from data in Ptolemy’s Geography and shows the coordinate system still being used, although the longitude values at the right-hand side are too high. The map is sometimes taken to show a flat earth, but that is a misunderstanding.

(Map by Johannes Schnitzer, 1482; public domain).

One of the medieval northern authors discussed in this paper, Adam of Bremen, seems to have wavered on the sphericity of the Earth. In his report on Vínland, he quotes a statement by Martianus Capella (1977, Ch. vi, §666) that “beyond Thule, the sea is congealed after one day’s navigation.” Then he says:

The very well-informed prince of the Norwegians, Harold, lately attempted this sea. After he had explored the expanse of the Northern Ocean in his ships, there lay before their eyes at length the darksome bounds of a failing world, and by retracing his steps he barely escaped in safety the vast pit of the abyss.

(Adam of Bremen, 2002, p. 220)

The “abyss” normally belongs to the flat Earth, but on the previous page Adam gives the usual convincing arguments for sphericity. On the other hand, there is no such ambiguity in the 13th-century texts of Rím 2 and King’s Mirror. They clearly know, for instance, how the land seems to sink into the sea when sailing away from land and how it rises again when the sailor climbs to the top of the mast. At the coast of a fiord, a bay, or a large lake, this is also seen by moving around while looking at the coast on the other side of the water. The Old Norse writers do not hesitate in attributing this to the Earth’s spherical shape (Beckman & Kålund, 1914–1916, pp. 104–105; Holm-Olsen, 1983, pp. 11–12). The same thought appears clearly and repeatedly in Das Seebuch, although the writers may not have fully grasped the concurrent message of sphericity (Koppmann, 1876, chap. A.X.6; A.X.16; B.VI.9; Sauer, 1996, p. 144).

Dante places his Purgatory in the Southern Hemisphere, antipodally to Jerusalem, and reports on the spherical shape of the Earth and its consequences for the visible sky, for travel, and for solar motion in the south (e.g., Dante, 2012, Purgatorio, Canto 4; Orr, 1956, passim).

The Daily Solar Cycle

Everywhere on Earth, solar motion can help with time reckoning, both during the day and the year, although methods will depend on the date and the place, especially the latitude. For example, solar motion in the Arctic or Subarctic is quite different from the more temperate zones or the tropics. In the subarctic, the best example of this is the phenomenon of bright nights around summer solstice, all the way down to about 58° from the equator, but unknown closer to the equator (U.S. Naval Observatory, 2004; Vilhjalmsson, 2006, pp. 365–366). They may also be compared to similar phenomena in the real Arctic (MacDonald, 2018).

Another example of variable methods concerns the daily motion of the sun along its path as a (rough) measure of time. In the tropic or subtropic zones, the sun is often high in the sky, making it somewhat complicated to follow its motion in a direct and quantitative way, although a gnomon or a sundial will help. But in the subarctic zone, the celestial pole is high in the sky and the diurnal arcs of the sun and the moon are oblique and may span almost all the horizon in summer. Roughly speaking, their projected motion along the horizon is even. This is reflected in several well-known modes of speech on time and solar motion in this region, both in medieval sources and in modern rural language.

A case in point is the Norse and Icelandic concept of eykt (octant). The word may be etymologically related to the number eight (Old Norse átta) and it means an eighth (3 h) of the 24-hour-long day and night (sólarhringur in Icelandic, døgn/dygn in Scandinavian languages). The octant points of day and night had special names as shown in Table 1.

Corresponding to the eykt, the Old Norse átt /ætt is an “octant of the horizon,” that is, 45° (Degnbol et al., 1995, p. 733; ONP, n.d.). By definition, during the time unit of the eykt the subarctic sun will move through an átt along the horizon.

Table 1. Names of the Old Norse and Icelandic Octants.

Local solar time


Rough translation

Local solar time


Rough translation

0 midnight



12 noon


high day, noon

3 a.m.



3 p.m.

nón, undorn, eykt


6 a.m.

miður morgunn


6 p.m.



9 a.m.


“day mark”

9 p.m.


“night mark”

Note. Some of the words in the table do not have any clear-cut meaning in terms of other words or concepts, so a translation cannot be given.

In Icelandic farms and villages up to the present, the so called eyktamörk, or octant marks, are quite common, being some landmark on the horizon, as seen from the farm, for instance, Miðmorgunshnjúkur (Mid-morning Peak), Dagmálahóll (Day Mark Hill), Hádegisskarð (Noon Pass). Note that these names may refer only to the farm in question; what is seen as a “Mid-morning Peak” from one farm might be a “Mid-evening Peak” for another on the opposite side of the peak.

The idea is that the sun should be above the octant mark at the corresponding eykt, for example, above “Noon Peak” at 12 o’clock local solar time. If this holds for a given day of the year, it will be so all through the year, within 10–20 minutes, but that is not so precise for other octant marks away from south. However, because medieval subarctic people had few other means of keeping time, the lack in precision may have been irrelevant for them.2

This is, of course, related to the concept of “unequal hours” used in the Middle Ages to cope with the varying length of day and night through the year. Chaucer, for instance, was familiar with it (Chaucer, 1996, “Knight’s Tale,” line 2271).

The Annual Cycle

Time reckoning through the year is a prerequisite in an organized society, although specific needs may vary with time and place. For instance, from 930 ce Icelanders had the Althingi, a general assembly where people gathered once a year for lawmaking and court hearings. Attendants spent two to five weeks away from home in a vital season. Because of long distances, lacking roads, and scattered population, Althingi could not be summoned by message as the Scandinavians did for their ting (assemblies). So, the Icelanders singled out a suitable date in summer, when the loss of domestic labor had minimal consequences. Late June was chosen for the purpose, after the lambs had been born in May and before haymaking in July. Then they constructed a simple and reliable calendar to tell them when to start the journey for the meeting.

Farming also benefits from a calendar for its annual cycle. For sure, the caprices of Icelandic climate may in some cases make the calendar an almost useless guide for action. In deciding when to let cattle and sheep out on grass or when to start haymaking, it may be better to observe nature itself than the calendar. But in other cases, the calendar is superior, like in determining when to sow the grain or let the ram to the ewes, so that the lambs have optimal prospect of growing during the short summer, avoiding bad weather at birth in the spring. When the farmer dates this action around Christmas, he has no relevant clues of terrestrial nature to follow.

There is a report on the Icelanders “standardizing” their year, in a way different from others and hence indigenous. It is written in the first decades of the 12th century about events from the 950s or so. That is within a century from the settlement, and some 25 years after the Althingi was started:

This was when the wisest men of the country had counted in two semesters [i.e., 1 year] 364 days or 52 weeks—then they observed from solar motion that the summer moved back towards the spring; but there was nobody to tell them that there is one day more in two semesters than you can measure by whole weeks, and that was the reason.

There was a man called Thorsteinn the Black; a very wise man. When they came to the Althing he sought the remedy that they should add a week to every seventh summer and see how that would work . . .

By a correct count there are 365 days in a year if it is not a leap year, but then one more; but by our count there are 364. But when in our count a week is added to every seventh year, seven years together will be equally long on both counts.

So, after the reform the average year was 365 days, which is still a quarter of a day too short. That is palpable in the long run and was remedied later, alongside with the gradual introduction of the Julian calendar in the 11th century (Vilhjalmsson, 1989, 1991).

But how was this done? People can, for instance, make a note of the location of the sun at sunset on a given day and then wait for 364 or 365 days to compare (Figure 4). The deviation of the sun from the initial location will show how to correct the year. And this is more or less accessible to common people, at least the more observant ones (Vilhjalmsson, 1997, 1999).

Figure 4. How could Thorsteinn the Black have found the length of the year? The southern slope of the mountain Eyrarfjall is straight west from Thorsteinn’s farm. At vernal equinox, the sun reaches the sea to the right of the mountain. Counting the days until that occurs again would tell him the length of the year to a day. Repetitions would improve the precision. (Vilhjalmsson, 1989, p. 94; drawing by the late Ólafur H. Torfason).

The introduction of the Julian calendar, which was just mentioned, did not solve every problem. The manuscript Rím 2 from the late 13th century states that the spring equinox is at March 21, which may seem correct. But the writer continues: “So it is at the centre of the world. But some people say it is about a week earlier in Iceland” (Beckman & Kålund, 1914–1916, p. 121; see also p. 175; author’s translation).

For sure, it was the intention of the church at the first Nicaean council in 325 that vernal equinox should occur on March 21, and so it was also in the 12th century, by decree of the Church. But because of the error in the Julian calendar, the real equinox had moved forward by three days every four centuries, summing up to a week at the time of writing. The “folk astronomer” Star-Oddi Helgason of the 12th century—who earned his living as a farmhand and fisherman but was known for his wisdom—dates the vernal equinox without further ado to March 15, and the solstices and autumnal equinox at time intervals of 13, 26, and 39 weeks from there (Beckman & Kålund, 1914–1916, pp. 48–51).

But Star-Oddi had more to say on the solar cycle. Oddi’s Tale is in three parts in Alfræði II (Beckman & Kålund, 1914–1916, pp. 48–53). The first describes, in intervals of one octant (3 h) how the exact timing of summer and winter solstices varies within the leap year cycle of 4 years. This does not seem to be based on observation but can be seen as an exercise in using the Julian calendar.

The second part of Oddi’s Tale contains the dates of the solstices as before and, in addition, the equinox dates. It also describes the variation of the declination, or the noon altitude, of the sun through the year, from winter solstice through spring equinox to summer solstice and back to winter solstice (Figure 5). Such information would be useful for transatlantic navigators, for instance, in keeping track of latitude. In Norse voyage reports, there are indications that this was used on the more difficult voyages (Vilhjalmsson, 2006) (see the subsection “Celestial Navigation”).

Figure 5. The variation of solar noon altitude through the year. The figure shows the reality in year 1149–1150 and the variation according to the second section of Oddi’s tale. The latter curve is normalized so as to yield the same maximum value as the other. It is composed of four parabolic sections that are mirror images of each other. The figure shows that this feature does not quite fit reality (Vilhjalmsson, 1991).

The third part of Oddi’s Tale describes the direction of dawn and nightfall through the year. Such observations depend on latitude, and hence their usefulness is limited. But the data given can be shown to fit Oddi’s alleged location in Northern Iceland, and so they add to the trustworthiness of the tale as a whole (Briem, 1914).

It is worth emphasizing that reports like the second and third part of Oddi’s tale show no clear indications of “imported” knowledge. The information is not either and is so refined as to render it incredible as deriving from experienced men in a society of seafaring and in close everyday contact with the powers of nature.

The Lunar Cycle

The most prominent trait of the moon is its phases, that is, its ever-repeating change from new moon to waxing moon, to full moon, and then waning back to new moon again, only to start the next cycle. The period varies slightly, but on the average it is 29.53 days, a lunar or synodic month.

While changing phases, the moon travels along the sky against the background of the fixed stars. But when it returns to the star where the last new moon was, the sun has moved further on in the same direction, and the moon has not finished its lunar month. The period for the motion along the firmament is called a sidereal month, and its length is 27.32 days.

In a sidereal month, the moon writes a great circle on the firmament, tilted by 5° relative to the ecliptic (solar path), which is again independently tilted by 23.5° relative to the celestial equator. Thus, the declination of the moon—and its pole distance—changes by 37°–57° back and forth in one month. This gave rise to a complaint in the King’s Mirror on the uselessness of the moon for navigation, as compared to the sun:

But these things tradesmen can hardly mark for the sake of their swift course because the Moon takes so large steps either up or down that people can for that reason hardly get their bearings from its courses. But the Sun can be relied on because it fills its courses more slowly both in ascending and descending and people can well determine all directions from its courses.

(Holm-Olsen, 1983, 10.17–19; author’s translation)

Certainly, the sun also changes its declination, but so slowly that it can easily be handled in finding latitude in the summer, especially if the navigator knows the formula for the change, for instance, from Star-Oddi.

The Cycles of the Tides

The motion of the moon is related to other cycles than those of the phases and its motion along the sky. People living at ocean coasts will normally see the tides, the more or less regular oscillations of the sea level at the coast. Seamen may also see oscillations in sea currents. Besides, the magnitude of the oscillations changes with time, between neap tide and spring tide. Furthermore, high tide does not occur at the same times today as yesterday, but some 48 minutes later on the average, and the oscillation spring tide—neap tide—spring tide has the average period of a half lunar month, spring tide having a locally determined delay up to a couple of days relative to full moon or new moon.

In its early days, astronomy evolved mainly in areas like the Mediterranean or even more inland where tides are either very small or invisible. It was not until the 8th century, when the Venerable Bede (672/673–745) came on the scene in Northern England, that the phenomenon received due scholarly attention. He was a well-known and prolific scholar, writing on many things from Church history to time reckoning and tides, which he studied in a large area around him. And the writers in Iceland and Norway were happy to report and support his results on the tides; they knew this from their daily life! (Beckman & Kålund, 1914–1016, p. 85).

Adam of Bremen is the first of the Northern authors studied here to mention the tides when he states that “the tide of the sea . . . rises twice a day” (Adam, 2002, chap. 42), quoting Macrobius and Bede. As already mentioned, this is incorrect, but the error is also found in the Icelandic manuscript Rím 1 from the late 12th century (Beckman & Kålund, 1914–1916, p. 48). It was corrected a century later in Rím 2, quoting Bede (Beckman & Kålund, 1914–1916, p. 85; see Bede, 2010, chap. 39, p. 95).

Das Seebuch gives a good practical treatment of the tides in Western Europe, both the periodical sea level variations and the tidal currents, how they correlate between localities, and how their rhythm follows the lunar motion, both in the diurnal displacement and the semi-monthly phases (Koppmann, 1876, passim; Sauer, 1996, pp. 167–177). This is, of course, based on local observations rather than learned calculations.

Chaucer refers to the neap and spring tides in an interesting way in “The Franklin’s Tale.” Dorigen is married to a knight who has promised never to force her obedience but is away for 2 years. Then Aurelius declares his love for her, but she replies that he must remove all the rocks at the coast where she used to stroll; then she would love him “best of any man.” He begs the god of the sun to ask his sister Luna (the moon) to go “no faster cours than ye,” so that they would keep an opposition and hence continuous spring tide for 2 years, and the rocks would vanish. The rest of the story is of no concern here, but it shows Chaucer’s acute understanding of the tidal cycles, especially the semi-monthly one and its relation to the solar and lunar motion (Chaucer, 1996, “Franklin’s Tale,” lines 815–1070; North, 1988, pp. 427–429).

The Lunisolar Cycle for Easter

In the beginning, Christians celebrated Easter at the time of the Jewish Passover. This was, however, not satisfactory to them in the long run. And as Christianity expanded, a rule was needed to determine a common date for Easter in widely separate places. Such a rule was approved at the first council of Nicaea in year 325 ce, referring to the vernal equinox and the full moon following it. Subsequently the need arose to predict the date beforehand, which requires sophisticated calculations. It gradually gave rise to a medieval branch of science called computus and the practitioners were called computists. Because communication was neither quick nor long-reaching in the Middle Ages, the Church needed many such experts for the whole Christian domain, although Easter tables were later circulated to help. Of course, the computists were respected and important people who mastered esoteric knowledge. When they are mentioned in medieval sources a recognition of their abilities often shines through.

Further discussion of the Easter cycle is not called for here, and interested readers are directed to other sources, such as the relevant works of Bede that are now available in scholarly English translations (Bede, 2004, 2010).

Celestial Navigation

It is well known from many parts of the Earth, that astronomy can be used for travel and navigation. When the magnetic compass arrived in Europe in the 12th14th century in Europe, it was initially only used in emergency when celestial navigation was not available, for instance in overcast weather (Sauer, 1996, p. 221).

In the main populated areas, the tropics and the parts of the temperate zones closest to equator, the conditions for using the stars for navigation are rather favorable: the night sky is often cloudless and dark, the stars are clearly visible, the Polar Star or the Southern Cross are at a convenient altitude, and there is a long period of complete darkness every night. However, in Northern Europe the sky may often be overcast; the Polar Star is inconveniently high; and north of 50–55°N, say, the nights of high summer will be brief and not dark. Furthermore, the weather conditions make sailing too unsecure out of summer, until motorized ships came on the scene (Marcus, 1980; Schnall, 1975). All of this calls for extra alertness and sharp observation for coping with the large and unfavorable North Atlantic ocean.

In Grænlendinga saga, one of the Icelandic sagas reporting on Vínland, a crew was going from Iceland to Greenland in overcast weather:

They put to sea as soon as they were ready and sailed for three days until land was lost to sight below the horizon. Then the fair wind failed and northerly winds and fog set in, and for many days they had no idea what their course was. After that they saw the sun again and were able to get their bearings; they hoisted sail and after a day’s sailing they sighted land.

(Sveinsson & Þórðarson, 1935, p. 246; translation Magnusson & Pálsson, 1965, pp. 52–53)

The phrase “get their bearings” probably means not only seeing the sun to find the cardinal directions, but also using the altitude of the noon sun to estimate their latitude (Vilhjalmsson, 2006). The land they sighted turned out to be in continental North America, but this time they did not go ashore there.

Later, people from the Norse Greenland colony made organized exploration and settlement voyages to the North American coast, ending in an area which they called Vínland. After a few winters around there, they remarked:

In this country, night and day were of more even length than in either Greenland or Iceland. The sun passed the points of octant and day mark in the period of the shortest days.

(Sveinsson & Þórðarson, 1935, p. 251; author’s translation, emphasis added)

This laconic remark indirectly states the unexpected fact that the climate on the East Coast of North America is—for them—colder than indicated by the solar motion, that is, from the latitude. They are then mainly comparing with the western coasts of Northern Europe that enjoy the beneficial warmth of the Gulf Stream (Bergþórsson, 1997; Vilhjalmsson, 2001).

The discovery and colonization of the North Atlantic islands, Faroes, Iceland, and Greenland, in the 9th and 10th centuries was at the verge of the technological capability of North European societies at the time, several centuries before the magnetic compass became really useful around 1300. Undoubtedly, knowledge related to astronomy was instrumental in this development at this stage, just as in similar cases in other parts of the world, for instance, in the Pacific Ocean. It can be seen—for example, from the numerous voyage reports in the sagas, that the Norse would have been unable to maintain regular transoceanic traffic without such knowledge.

This appears again somewhat further south in Das Seebuch. For “getting the bearings” in the book’s domain, navigators can use either the sun at day or the Polar Star at night, and there are examples of both methods (Sauer, 1996, pp. 163–167). The book also confirms the ideas presented here of celestial navigation before the compass. In the beginning, at the end of the 13th century, the compass was used only in cases of emergency (overcast weather), but by the end of 14th century at the latest, it was used as a real and reliable instrument (Sauer, 1996, p. 180).

The Weekday Names

The history behind weekday names in European languages is both complicated and interesting. The story began in ancient Greece with the people giving the names of their gods to the five star-like planets. Adding the sun and the moon (who were also gods), the names of these seven “planets”—and the corresponding pagan gods—were attributed to the weekdays by a rule based on the ordered system of Heraclides of Pontus: moon, Mercury, Venus, sun, Mars, Jupiter, and Saturn (Dreyer, 1953, p. 169; Kren, 1986).3 This reflects, although indirectly, the alleged distance of the planets from the Earth, the center of the geocentric system of the time (see Figure 1). This leads to the ordered weekday names used in most present-day Romance languages, with some exceptions, like the Lord replacing the sun and Sabbath replacing Saturn in some cases, and numerals replacing the pagan gods in Portuguese.

The spokesmen of Christianity in its first centuries tried to fight this “pagan” system, although with little avail (Falk, 1999) as shown by the few exceptions mentioned. When the seven-day week spread to the North, the Germanic people adopted the same name system, replacing each Roman god by the corresponding one of their own. Thus, for instance, Old English has the series Sunnandæg, Mōnandæg, Tīwesdæg, Wōdnesdæg, Þunresdæg, Frīgedæg, Sæternesdæg. There is, however, no clear indication that these Germanic names were associated with Greek and Roman gods and subsequently the planets. The German Mittwoch (Midweek) and the Norse laugardagur/lørdag (Wash day) are the main deviations from the Old English in the Germanic world, presumably for the same reason of Christian interest. Also, the Icelandic bishop Jón Ögmundarson of the early 12th century disliked the reference to pagan gods, so he introduced names based for the most part on the cardinal numbers as seen in many languages outside the Romance and German regions.

The Romance weekday names certainly reveal an early interest in the planets, on behalf of the society. They can be seen as a linguistic relic from the past, similar to the more palpable or archaeological ones.


This article has focused mostly on folk astronomy in medieval Northern Europe, using available written sources on this topic from that region. Written sources from the Southwest are also obtainable, but the more advanced astronomy in them tends to eclipse the folk astronomy. Similar written sources from Eastern Europe are scarce, but archaeological relics, which fall outside of the scope of the present article, are available.

Because astronomy is useful in several important contexts of everyday life, it seems likely that some kind of such knowledge has existed among common people almost everywhere in organized human societies. However, the emphasized subjects within the field may vary from one society to another, often related to natural circumstances, ways of living, modes of production, religion, and so on. People from agrarian cultures tend to observe the sun and the seasons; navigators on sea or in alien land make use of the sun, the moon, and the stars; maritime people at ocean coasts benefit from knowing the tides and lunar motion; traditions of religion often draw on details of astronomy or calendar; and so on.

Medieval sources on European folk astronomy can be found in various places, ranging from poems like the Edda and the works of Dante and Chaucer, to the sagas and historical writings like those of Adam and Saxo, to encyclopedic works and handbooks like King’s Mirror and Das Seebuch. This broad spectrum of sources reflects the fact that folk astronomy is concerned with phenomena of daily life, and knowledge of them can be both interesting and useful.

There may also be food for thought in looking at folk astronomy through the glasses of a general history of science. The reader may then realize that folk astronomy seems to develop parallel to astronomy itself, from the simple pictures of the early Middle Ages to a more multifaceted view at the end, with more and more applications in all kinds of more developed activities, like navigation, varied agriculture, and so on, together with a more evolved society, awaiting social changes like the renaissance, discoveries of new lands, printing, universities, manufacture, and so on. The modern era was ahead.


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  • 1. In the title of the article the term “planet” refers to Mercury, Venus, Mars, Jupiter, and Saturn, although it would also have included the sun and moon in ancient and medieval times. The article also treats some of the more astronomical aspects of the Earth, like its spherical shape.

  • 2. Stephen McCluskey (1998, pp. 4–10) has a concise discussion of what might be called “everyday astronomy” or “naked eye astronomy” and is the underlying theme in these subsections.

  • 3. Each of the 24 hours of each weekday were cyclically attributed to one of the planets in this order. The first hour of Saturday belonged to Saturn, and the remaining days obtained their name from the planet of its first hour. In this way the Heraclidean order of the planets led to our well-known order of the weekdays: sun, moon, Mars, Mercury, Jupiter, Venus, and Saturn (see, e.g., Richards, 1998, pp. 268–273).