Coligny Calendar - System

System

The Continental Celtic calendar as reconstructed from the calendars of Coligny and Villards d'Heria had the following properties:

• it was a lunisolar calendar, attempting to synchronize the solar year and the lunar month.
• the months were lunar. Scholars disagree as to whether the start of the month was the new moon or the full moon, or per Pliny and Tacitus perhaps even the First Quarter.
• the common lunar year contained 354 or 355 days.
• the calendar year began with Samonios, which is usually assumed to correspond to Old Irish Samhain, giving an autumn start to the year. However, as Samon is Gaulish for summer (Lambert p. 112), this assumed start is disputed. Le Contel and Verdier (1997) argue for a summer solstice start of the year. Monard (1999) argues for an autumn equinox start. Bonsing (2007) argues for a May beginning consistent with Irish Beltaine, and Fennian literature, notably Joyce (2000).
• the entry TRINOX SAMO SINDIV "three-nights of Samonios today") on the 17th of Samonios suggests that, like the Irish festival of Samhain, it lasted for three nights. The phrase *trinoxtion Samonii is comparable to a Gaulish festival mentioned in a 1st century AD Latin inscription from Limoges, France, which mentions a "10 night festival (*decamnoctiacon) of (Apollo) Grannus" (POSTVMVS DVNORIGIS F(ILIVS) VERG(OBRETVS) AQVAM MARTIAM DECAMNOCTIACIS GRANNI D S P D )
• the solar year was approximated by the insertion of a 13th intercalary month every two and a half years (unlike the Islamic calendar, where the calendar year keeps shifting in relation to the solar year). The additional months were intercalated before Samonios in the first year, and between Cutios and Giamonios in the third year. The name of the first intercalary month is not known with certainty, the text being fragmentary; the second intercalary month is Ciallos bis Sonnocingos (Lambert p. 116)
• the months were divided into two halves, the beginning of the second half marked with the term atenoux or "renewal" (cf. Old Irish athnugud "renewal"). The basic unit of the Celtic calendar was thus the fortnight or half-month, as is also suggested in traces in Celtic folklore. The first half was always 15 days, the second half either 14 or 15 days on alternate months (similar to Hindu calendars).
• months of 30 days were marked matus, lucky. Months of 29 days were marked anmatus, unlucky.
• a simple five year cycle would be insufficiently accurate; the sequence of intercalary months is completed every thirty years, after five cycles of 62 lunations with two intercalary months each, and one cycle of 61 lunations, with a single intercalary month, or after a total of 11 intercalary months. This assumes that there are exactly 371 lunations in 30 years, which is accurate to a one day every 20 or 21 years on average (this is less accurate than the Julian calendar, which shifts a day in about 130 years, but which ignores lunar months). It may be assumed that the "30 years cycle" was not prescriptive, and that an extra month would have been omitted as the need arose (i.e. some 300 years after the calendar's inception).