Coligny Calendar

In 1897, a fragmented bronze calendar was discovered in Coligny, France. It is believed to date from around 50 BC and appears to be the remains of a Romanized Gaul model of a Celtic lunar and solar calendar.

It displays a cycle of about five years on 62 tables. Unlike our present day calendar, courtesy of Julius Caesar, this system used the accurate period of the moon's orbit around the Earth, the lunar month, to measure the passage of time. Each lunar month corresponds to 29.53 days. In the Gaul model, the month was divided into two 15 day periods.

Now, a solar year, the time taken by the Earth to circle the sun, or one revolution of the sun about the Vernal Equinox, is nominally 365 days. Twelve revolutions of the moon, however, equal only 354 days. The Coligny Tablet/Calendar had to make two adjustments: first using alternate months consisting of 29 and 30 days; second, adding a month every 2 1/2 or 3 years to link up the shorter lunar year of 354 days to the solar year of 365 days.

In Celtic legend, the new year started on the moonrise of the first last-quarter moon after the Autumnal Equinox. In the Celtic regions of Britain and Ireland, the tradition was held so that the new year started at Samhaim, see Pagan Holidays (November 1) so that it would always occur on the same day of the solar cycle

The Coligny Calendar is a series of stone tablets dating to the time of Julius Caesar; it is a record of the Gaulic (and thus Celtic) year, though it shows some Roman influence, as Roman numerals are used. However, the names of the month are given in Gaulic, and the year begins in November, keeping with what we know of the Celtic year. The calendar is both a lunar and solar calendar, which causes some problem with drifting, but this was accounted for by their astronomers (yes, the Druids). The calendar uses a mathematical arrangement to keep a normal 12 month calendar in sync with the moon by adding an extra month every 2 1/2 years.

Us         Gaulic             Meaning                  Designation  Length
           
November   Samonios           "Summer's End"               MAT        30
December   Dumannios          "Dark Month"                 ANM        29
January    Riuros             "Frost Time"                 MAT        30
February   Anagantios         "Indoors"                    ANM        29
March      Ogronios           "Cold"                       MAT        30
April      Cutios             "Windy"                      MAT        30
May        Giamonios          "Winter's End"               ANM        29
June       Simivisonnos       "Semi-Spring" or Midsummer   MAT        30
July       Equos              "Horse Month"                ANM        29
August     Elembivios         "Many Fences"                ANM        29
September  Edrinios           "Hot Time"                   MAT        30
October    Cantlos            "Song"                       ANM        29
           Ciallos (intercalculatory month)                MAT        30

ANM meaning "Bad" and MAT meaning "Good"; notice the good months are all 30 days, and the bad months 29. Also notice that February has been considered bad and short for over 2000 years. BTW: Samonios is of course the same as the Irish "Samhain"

Now, according to The Gallic Wars: "All the Gauls assert that they are descended from the god Dis, and say that this tradition has been handed down by the Druids. For that reason they compute the divisions of every season, not by the number of days, but of nights; they keep birthdays and the beginnings of months and years in such an order that the day follows the night."

And, in reading Pliny's statements on the Druids supposed custom of cutting the mistletoe on the sixth day of the moon, it has been assumed that the month began on the new moon, like the Jewish calendar. Actually, it has a lot of similarities to the Jewish calendar, which leads to an interesting question--did the Celts have contact with the Jews before they migrated west?

According to Ray White, "the era of the New Coligny Calendar (NCC) {began} on October 8th, 1999. This date was chosen because this date corresponds with a new moon on the date of the beginning of European winter. (when the sun is at 15Deg Scorpio)" which is also the day that the megalith at Tara marks the beginning of winter--the day the sun is at 15º Scorpio.

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Sources:

Jean Markale: The Pagan Mysteries of Halloween

Ray White's Coligny Calendar page: http://technovate.org/web/coligny.htm

The problem of Ciallos

This calendar has been documented here quite well, but the former writeups in this node fail to address the fact that the intercalary year does not completely correct the calendar such that it aligns perfectly with the solar year; even with an intercalary 30 day month every 2.5 years, there is still drift between the Coligny calendar and the solar year; without the correction, the calendar is 11.25 days short. With the intercalary month, the average year's length is 366, which overcompensates 0.75 days per cycle. In ten years, this is a 7.5 day drift. In a lifetime, the calendar will drift forward two entire months.

One moon cycle lasts 29.5 days -- there are six 29 day months, and six 30 day months. In total these lunar months average to 254 days in a lunar year -- here is the 11.25 year discrepancy between the lunar and solar year. To calculate the offset of the discrepancy, I used the following calculations:

My calculations

(Days in three Coligny years with adjustment) == 354 days per year * 2.5 years + 30 intercalary days = 915 days per 2.5 years

(Days in 2.5 solar years) == 365.25 days per solar year * 2.5 years = 913.125 per 2.5 years

... and processing these numbers ...

(drift in 2.5 years) ==915 Coligny days - 913.125 Solar days = 1.875 days

(drift in 1 year) == (drift in 2.5 years) / 2.5 = 0.75 days

(Solar years per Coligny year) == 915 / 913.125 = 1.0020533881

(drift in 80 years) == (Solar years per Coligny year) * 80 years = 0.164271048 solar years = 60 days!!!!!!

As you can see, this drift, seemingly small, can be very problematic. We don't know how the Gauls corrected this drift; presumably a mathematician (in this case a druid) added or removed days here and there to keep the calendar in line. The majority of people in celtic Gaul were illiterate, there was no Gaulish script, and the Coligny calendar was discovered in Romanized Gaul, written in Latin; thus, no surviving record of the method of correction exists. All we can do is interpret and correct this issue ourselves.

A seemingly obvious (but poor) fix

The obvious potential fix is to add an intercalary 33.75 days every 3 years. This will keep the months at 29.5 days in length, but adjust the average year length to align with the solar year. While a fractional day can't be added every three years, the .75 could be could be added as three leap days every 12th year.

(fixed days per three years) == 354 days per lunar year × 3 years + 33.75 days = 1,095.75 days.

(fixed days per year) == (fixed days per three years) / 3 years = 365.25

The problem with this hypothetical fix is that, once a intercalary year has occurred, the months no longer begin on the new moon. For example, lets say that at the calendar's inception, every month begins and ends on the full moon. The first day of Samonios after an intercalary year is a waxing crescent moon, as do the following months. If I were to throw the three leap days, 12 years after inception, let's say I hypothetically throw them at the end of Ogronios, all months following Ogronios (Cutios, Giamonios, etcetera) the first days of those months will begin on a full moon. Additionally, at the beginning of the twelfth year, before the leap days, the months begin on a waxing gibbous.

Conclusion

I have spent my entire day and most of yesterday playing with this calendar, trying to get it to work. I can't come up with a fix that preserves months beginning and ending on full moons, likely because the entirety of my math knowledge stops after college algebra, and that was years ago. I will keep pondering this and see if I can eventually find a way, but if anyone here would like to give it a try, go right ahead. If you can fix it, shoot me a message please and I will add it to this writeup (with credit of course!)