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Misseri-calendar - The Icelandic Week-based Calendar

Author(s): 
Kristín Bjarnadóttir (University of Iceland)

Certain calendar features were familiar to all the settlers, who mainly came from the fiords of Western Norway, with slaves from Ireland and the British Isles. These features included a seven-day week [3], with several of the days named after Norse gods that in turn correspond to Roman gods whose names remain visible in the weekday names of some Roman languages.

  • Sunday, the day of the sun

  • Monday, the day of the moon

  • Tuesday for Tyr, the god of war

  • Wednesday for Woden, the cunning god

  • Thursday for Thor, the thunder god

  • Friday for Freyr / Freyja / Frigg, the god and goddesses of love and marriage

  • Saturday, laugardagur, the day of bathing.

The names related to the pagan gods remain even today in English and most Nordic languages. In Icelandic, they were abandoned by the Church in the twelfth century in favor of the names thridjudagur (Third Day) for Tuesday, midvikudagur (Mid-week Day) as in German for Wednesday, fimmtudagur (Fifth Day) for Thursday, and föstudagur (Fast Day) for Friday. Together with the names sunnudagur, manudagur, and laugardagur for Sunday, Monday, and Saturday, these names have remained intact to this day.

Initially, some of the illiterate settlers probably also tried to count time according to the cycle of the moon, 29.53 days, but by the end of the settlement period in year 930 the months were standardized to 30 days each. Although there is no definitive written evidence as to why Icelanders abandoned the lunar months, reflecting on the visibility of the moon as an inhabitant of Iceland suggests several plausible speculations. For example, the moon is often low in the sky at northern latitudes, and the sky itself is frequently cloudy. The nights in Iceland also remain light from April until late August, so that the moon can rarely be seen in the summer, even when it is full. Reasons such as these may explain why counting the lunar months in summer was abandoned, and counting the summer weeks was instead adopted. Moreover, frequent low-pressure areas visiting Iceland cause the sky to be covered with clouds for long periods of time in wintertime, as well as in summer. The fact that the moon cannot be seen regularly in winter due to these difficult weather conditions may also have contributed to the eventual standardization of the winter months to 30 days each [4].

Íslendingabók [The Book of Icelanders, Libellum Islandorum] was written by Ari the Learned in the period 1122–1133. It survives in manuscripts from the seventeenth century. According to this book, an agreement was reached at the yearly parliamentary gathering in the year 930 to meet again after 52 weeks, or twelve 30-day months and four extra nights. Timekeeping by means of counting the weeks and the standardization to 30-day months appears thus to have been formally agreed upon simultaneously. In accordance with this new calendar, the year was divided into two terms, or misseri, with the summer-misseri to last six months, the winter-misseri to last another six months, and four extra nights to be added at midsummer [5]. The year began with the summer-misseri, which began on the First Summer Day (presently in the latter half of April). Interestingly, computing time by counting the 30-day remained a stronger habit among the general public through the centuries during the winter-misseri from January to May than it did during the summer-misseri.

The error in this system of computing time with a 364 day-long calendar year was quickly realized. By the 950s it had become clear that the summer “moved back towards the spring,” i.e. the summer according to this calendar began earlier and earlier vis-à-vis the natural summer. This was inconvenient, as the parliamentary gathering had to assemble after the completion of certain necessary farming tasks, such as lamb-births, and before others, such as hay-making, were due to begin. This problem and the discovery of a possible solution are recorded in The Book of Icelanders (all Icelandic passages in this article have been translated by the author) [5]:

This was when the wisest men of the country had counted in two misseris 364 days – that is 52 weeks, but twelve thirty-night months and four extra days – then they observed from the motion of the sun that the summer moved back towards the spring; but nobody could tell them that there is one day more in two semesters than can be measured by whole weeks, and that was the reason. But there was a man called Thorsteinn Surtur … when they came to the Althing then he sought the remedy … that every seventh summer a week should be added and [they would] try how that would work

The error might have been realized by Thorsteinn Surtur from observations of the location of the sunset, which in northern areas moves clockwise along the horizon before the summer solstice, and subsequently anti-clockwise. Below, we see the view to the west from Thorsteinn Surtur’s farm at 65° N latitude. Only at summer solstice does the sun set just north (just to the right) of Eyrarfjall [6]. Simulations of the Sun track (or Sun path) related to this phenomenon are described in the next section of this article. 

Figure 1: The view to the west from Thorsteinn Surtur’s farm at 65° N latitude.
(Photographer: Grétar Eiríksson)

According to the source cited above [6], Thorsteinn Surtur recommended in year 955 that every seventh year an extra week be inserted at midsummer, Summer’s Extra Week, making the average year 365 days. By the year 1000, the parliament gathered after ten weeks of summer had passed, instead of nine weeks, an adjustment that was needed because the eleven leap years since the year 955 had also caused another, but slower, “move back towards the spring.” The Book of Icelanders says simply [7]:

Then it was spoken the previous summer by law, that men should arrive at Althingi when ten weeks of summer had passed, but until then it had been a week earlier.


[3] Björnsson, Á. 1993. Saga daganna, pp. 18–19. Reykjavík: Almenna bókafélagið.

[4] Richards, E. G. 1998. Mapping Time: The Calendar and its History, p. 204. Oxford: Oxford University Press 1998.

[5] Benediktsson, J. (ed.), 1968. Íslendingabók. Íslensk fornrit I, 1. pp. 9–11. Reykjavík: Hið íslenska fornritafélag.

[6] Vilhjálmsson, Th. 1990. Raunvísindi á miðöldum. In Frosti F. Jóhannsson (ed.). Íslensk Þjóðmenning VII. Alþýðuvísindi. Raunvísindi og dulfræði, pp. 1–50, 271–273. Reykjavík: Þjóðsaga.

[7] Benediktsson, 1968, p. 15.

Kristín Bjarnadóttir (University of Iceland), "Misseri-calendar - The Icelandic Week-based Calendar," Convergence (July 2016)

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