Our Recreation of the Viking Calendar
Historians today do not know the exact format of the Viking calendar. So our
goal here was to re-create one, following Viking calendar rules as we understood them to be.
We did not want an Icelandic calendar (that's something quite different).
Our intent was to create a working calendar that any Viking would be proud. (Heck,
we figured anyone can create an inaccurate calendar, but where's the fun in that?)
We started with a couple of assumptions:
- The Vikings were smart.
- The Vikings had a particular fondness for the Summer Solstice, the number 7,
and the number 364.
- Because of item (1), the Vikings would not tolerate an inaccurate calendar.
So our re-creation needed to be a working calendar, that could be used today,
good enough to make any stray Viking proud.
We started with what we knew about their calendar.
We knew
- The Vikings split their year into 2 equal
halves: Summer and Winter.
- The length of the summer season and the
winter season was the same: 26 weeks each.
- The length of a regular year was 364 days.
- The length of a Viking week was 7 days.
- The Viking year was subdivided into 12 smaller units.
- The summer solstice was the single most important
astronomical event to the Vikings.
- The Vikings did have a leap year system, although there
is absolutely no agreement on what it was and how often it was applied.
We did not know
- The exact placement of the start of the Viking
year. We surmise that since the Viking year was in 2 equal halves, then Midsummer
(Summer Solstice) must come mid-point in the summer season. If Midsummer
comes midway in the Summer Season, then the year must begin 91 days prior
to midsummer. Some people have argued that the year began on the Summer Solstice, (midsummer).
We feel that midsummer means the middle
of summer. It is not called startsummer
it is called: midsummer. We realize we've belabored this point a bit, but this one is a biggie ...
- The length of each of the 12 units (or months).
We reasoned that since the number 7 was very important, each month would
be a multiple of 7: either 4 or 5 weeks in length. (28 or 35 days). We already
knew that each half of the year was a multiple of 7:
7 x 26 = 182
It was no great leap of imagination to fit 182 days into 6 months of 7 days per week
with even multiples of 7. The pattern we chose, was, the one that made the most sense in
dealing with the leap year.
- The year number. We decided since Thorsteinn the Black
fixed their calendar in 955, that became year 1. The start of the Viking year was
actually 91 days before midsummer in the year 955.
Now we get creative and try
to figure out the leap years!
We knew
- In the Julian year 955, Thorsteinn the Black
discovered discrepancies in the Vikings calendar and implemented a leap year system,
that was presumably still accurate and in effect during the Golden Age of Icelandic
literature (c. 1200).
- We know Thorsteinn the Black called for adding
an additional 7 days every 7 years.
- We know that just adding 7 days every 7 years is
not enough. The calendar will drift in time. Yet, presumably, it did not
drift, because the Vikings were smart.
This is what we did:
- Every 7th year became the calibration year.
The 7th year began 91 days from the Summer Solstice, putting the extra days (sometimes
8, sometimes 7) at the bottom of the 6th year.
- There are 2 kinds of leap years:
1. Those that add 7 days to the year (making a year length of 371 days)
2. Those that add 8 days to the year (making a year length of 372 days)
In year with 371 days,
- 7 days are added to Month 12. Month 12 in a regular
year is 28 days in length.
In a leap year, it has 35 days.
In year with 372 days,
- 7 days are added to Month 12, and 1 day is added to Month 11.
- Month 12 in a regular year is 28 days in length.
In a leap year, it has 35 days.
- Month 11 in a regular year is 28 days in length.
In a leap year, it has 29 days.
This was just some of the things we had to work with
(from the Book of Icelanders, written by Ari the Learned in 1122-33 discussing the
calendar reform of 955):
This was when the wisest men of the country had counted in two semesters 364 days or
52 weeks-then they observed from the motion of the sun 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 try 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. But if there are
2 leap years between the ones to be augmented, you need to add to the sixth.
Reading between the lines ..
- There does seem to be a special handling case for certain leap years: But if there are
2 leap years between the ones to be augmented, although the meaning is rather
obscure.
- When we started to really study the summer solstice, and the year length
of 364 days, the leap year length did have a certain pattern about it:
372, 371, 371, 372, 371, 372, 371, 372, 371, .... (this is just a tiny snippet) which might be what is being described.
The Net Result
Our re-created Viking calendar is as accurate today as it was in 955. It retains the spirit of the Viking calendar - in terms of month length and year length; it is continually recalibrated on the 7th year. We may be wrong, but we haven't seen a description of rules that we can use and really understand. If the Vikings did not allow for calendar drift, that would negate assumption (1) ("The Vikings were smart.") and since The Moose has Viking ancesters, this thinking is not allowed.
Moose approved interpretation
For Those Who Want Even More Information
The thinking behind the Viking Calendar was that we wanted to create a
calendar that was totally pre-Christian, devoid of Christian influences. This is not being anti-Christian, it simply a recognition that the Vikings were not Christians and had evolved their own methods
for calculations. Here's a little of our reasoning.
In studying calendars from so many cultures, we've also studied
the methods used by the ancients for creating that calendar. In his work, Astronomical Algorithms,
Jean Meeus gives some great algorithms for converting the Gregorian calendar to the Jewish calendar.
The only problem is that the algorithm fails at a certain point. We all know that Patriarch Hillel II
did not devise the Jewish calendar with such lines as:
if j = 1 and a > 6 and r > .632870370,
then D = (integer portion of) Q + 24;
... etc.
Likewise for the Persian calendar, or the Mayan calendar.
We also know that people like Galileo were able to calculate the area of a curve without calculus
(it wasn't invented yet). He certainly didn't have computers or even a slide rule. So, our thinking was to
reconstruct a Viking calendar using the mathematical tools that would have been available at the time.
So how did people do it? Well, we considered that in any society (and ours is no exception) there is a very
small percentage of people who can actually understand a particular topic thoroughly. A good many others have a
general broad knowledge, the vast majority learn by rote and do by rote without knowing why. This is not an insult.
This is just the way it is. Take computer design for example. There are just a handful of people on this planet
who could design from scratch a computer using only vacuum tubes, resistors, diodes. A good many others could
buy some pre-manufactured computer boards and assemble them to create a working desktop (but they wouldn't know
how to build the boards), while the vast majority know how to turn it on and interface with the program of their choice.
We see the exact same parallel with understanding the heavens. There would be a handful of very adept and
clever Viking astronomers who knew not only the sky but knew why certain constellations appear at certain times.
They would have some very clever and accurate observations. These in turn would be translated into tables.
The tables becomes the Bible for their navigation.
Johannes Kepler only came up with his laws of planetary motion only after the painstaking and methodical
data collection of Tycho Brahe. Every day for 20 years or more at the same time, same location, Tycho Brahe
turned his telescope onto the heavens and jotted down his findings. Brahe had no idea what he was seeing,
but continued the painstaking data collection anyway. Kepler saw in Brahe's data, the planetary orbits as ellipses.
There's nothing in the historical record that says Thorsteinn the Black didn't reply on others for his calendar rules.
History remembers Kepler more than Tycho Brahe. Yet Kepler could not have advanced his laws without Brahe's research.
Why couldn't Thorsteinn the Black be the Viking equivalent of Johannes Kepler? We decided that rarely does someone
invent in a vacuum, Thorsteinn the Black probably had gobs of data from years and years of practical data collection
at his fingertips - all collected by others. It was Thorstein the Black who created the rules.
And what were the rules? Obviously, this gets highly speculative, but as we started this road, no sense stopping now.
As mentioned before, many very elaborate calendars could be expressed in a series of tables. Finding the year
length would be something like: "for this class of year, go down column A, until it intersects with row B
and use that number as an index into table C". The normal person who is consulting a calendar by rote would
not know why the significance of row B or the index pointing to table C, just that he has to do it.
He would also know that he always gets the right answer. Its the Johannes Keplers and Thorsteinn Blacks of
the world that create the tables in the first place.
The more we looked at the data the more we saw a pattern. If we use as our base the fact that Viking year
length is 364 days, we know it has to be recalibrated. Sometimes by 8 days, sometimes by 7 days every 7 years.
Without the recalibration, the calendar would fail. We figured anyone could create a bad calendar, we wanted to
create a predicable calendar. So the trick was trying to understand when 8 days were needed and when 7 days were
needed. We simply pretended we were Tycho Brahe collecting data. We started with the summer solstice in year 955 and
imposed a 364 day year for 6 years. We then went to the next sumer solstice, determined what that year length would
be and jotted its year length down. We looked at the years backwards and forwards from our starting point.
We looked at thousands of years. Lo and behold we morphed in Johannes Kepler as we did find a predictable pattern
in the year lengths. There was a pattern about it. All that data could be reduced to a table driven year-length
calendar. For 6 years the year length is 364 days, then for the next year, go down column A, until it intersects
with row B and use that as the index for table C. The answer will either be 371 or 372 days.
We have no idea if this is what the Vikings themselves did. But we did discover a method that is in keeping
with the spirit of ancient calendar methods. It is predictable, and it is accurate. It is the kind of calendar
that the ordinary Vikings would not know why the significance of the index at row B, but they know that they
would always have the right answer.
Christianity imposed a rule set that is far easier to learn without tables. In the 12th century the Christian
calendar rule was: every 4 years there is a leap year. That's it. Nothing else. The more we studied the
Viking calendar, the more we realized that the Christian rule does not pay homage to the Vikings as astronomers or
sea men. And if you remove the "every 4 years there is a leap year" rule what on earth do you put in its place?
Of all the calendars (so far), the Viking one has been the most fun. Second place is the Jewish calendar
when we decided to reconstruct the techniques used by Patriarch Hillel II. We have no idea if we're onto something,
or not. But we know we have a calendar that is highly accurate, it uses ancient methods of calculation, it is in
keeping with the spirit of the Viking calendar not unlike modern boat builders who recreate Viking ships using
the original tools. Its just a different way of looking at the same problem.
Calendar Articles - Our Reconstruction of the Viking Calendar
