Lunar Calendars

Lunar Calendars

Our ancient Ancestors marked time by the phases of the Moon - from excavated tally sticks archaeologists have been able to deduce that people were  counting days this way as early as the Palaeolithic age.

A month is a unit of time, used with calendars, which is approximately as long as a natural period related to the motion of the Moon; month and Moon are cognates (have the same etymological source). The traditional concept arose with the cycle of moon phases; such months (lunations) are synodic months - a synodic month is the time interval between two consecutive occurrences of a particular phase (such as new moon or full moon) as seen by an observer on Earth, and last approximately 29.53 days.

A slight problem arises with the fact that there are 13 full moons (or new moons) in a year and as the seasons of the year are governed by the movement of the Earth in relation to the Sun (put simply) it makes it difficult to make an accurate rule-based calendar that takes both into account. The most common solution to this problem is something called the Metonic Cycle which is based on the fact that 235 lunations are approximately 19 years - a Metonic calendar only drifts out of sync with the seasons by approximately 1 day every 200 years. It was this cycle that was used in the Antikythera Mechanism about 2000 years ago.

We know that our ancient ancestors marked the movements of the Sun from the alignments of stone circles which mark the solstices and the Coligny Calendar (Gaul 2nd C - CE) is described as another attempt to reconcile both the cycles of the Moon and the Sun, it is believed that this system may have been in use for 1,000 years and would have pre-dated the Celts.

Did our ancient ancestors - the hunter gatherers and their descendants who built the stone circles try to reconcile these two systems? Did they need to? Surely it is feasible that they could have used the Moon's phases to mark their days and the Sun's movement to mark the turning cycles of the seasons.

Full Moon and Lunar Month Names

Date Range

Generic Celtic Moon



Coligny Calendar

Lunar Month

Dec - Jan

Wolf Moon,  Stay Home Moon

Moon after Yule

Riuros - (Cold time)

Jan - Feb

Storm Moon,  Ice Moon, Snow Moon

Wolf Moon

Anagantios - (Stay-home time)

Feb - Mar

Plough Moon,  Wind Moon, 

Lenten (lengthening) Moon

Ogronios - (Ice time)

Mar - Apr

Budding moon, New Shoots Moon,  Seed Moon

Egg Moon

Cutios - (Windy time)

Apr - May

Mothers' Moon, Bright Moon, 

Milk Moon

Giamonios - (Shoots Show)

May - Jun

Mead Moon, Horse Moon,

Dyan Moon, Rose Moon

Flower Moon

Simivisonios - (Bright time)

Jun - Jul

Claiming Moon,  Wyrt or Herb Moon,  Mead Moon

Hay Moon

Equos - (Horse time)

Jul - Aug

Dispute Moon, Lynx Moon

Grain Moon

Elembiuos - (Claim time)

Aug - Sep

Wine Moon, Song Moon

Harvest Moon

Edrinios - (Arbitration time)

Sep - Oct

Blood Moon,  Seed Fall Moon

Hunters Moon

Cantlos - (Song time)

Oct - Nov

Mourning Moon,  Darkest Depths Moon

Blood Moon

Samonios - (Seed-fall)

Nov - Dec

Oak Moon,  Full Cold Moon

Moon Before Yule

Dumannios - (Darkest Depths)

The Coligny Calendar

Q. When is a Calendar not a Calendar?

A. When it is an Almanac

According to Wikipedia – ‘The Coligny calendar is a peg calendar (or parapegma) made in Roman Gaul in ca. the 2nd century AD, giving a five-year cycle of a lunisolar calendar with intercalary months.’

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.
  • 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 consistant with Irish Beltaine, and Fennian literature, notably Joyce (2000).
  • The entry TRINVX[tion] SAMO[nii] SINDIV "three-nights of Samonios today") on the 17th of Samonios suggests that a festival of Samhain was considered to last for three nights.
  • 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 Giamoniosin 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. 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 Mat(os), lucky. Months of 29 days were marked Anm(atos), 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).
  • The interpretation of atenoux as "returning night" is improbable (Delamarre p.58) and "renewing" would seem more probable; thus the month would start at new moon and atenoux would indicate the renewal, ie the full moon.             (


“The word parapegma (pl.: parapegmata] refers to an ancient instrument which was used to keep track of astronomical, astrological or astrometeorological cycles using a moveable peg or pegs. By extension, the word also refer to a group of texts which were derived from these instruments, and which tracked the astrometeorological cycle typically by linking it to a calendar.

 …  they provided some means for locating the current day in the context of the larger temporal scheme, either by indexing the cycle to a calendar, or by indicating the current day with a peg. I call this process tracking a lunar or astrometeorological cycle. In inscriptional parapegmata, each entry would have a hole drilled beside it to receive a moveable peg. The peg would be shifted on each consecutive day, and thus the inscription beside the peg would contain the information pertaining to the current day.

There were also non-inscriptional, literary parapegmata in both Greek and Latin. A typical example of these would list the dates of a coming year in, for example, the Roman or Egyptian calendar, and, for particular dates, offer astronomical and weather predictions for that year. In this respect, they are rather like a pared-down version of a more modern Farmer’s Almanac.”


Astronomy, Weather, and Calendars in the Ancient World: Parapegmata and Related Texts in Classical and Near-Eastern Societies                                                                 Daryn Lehoux (Cambridge University Press 2007)

The importance of long-term weather prediction is invaluable to farmers – ‘Make hay while the Sun shines’ – today with modern weather forecasting and machinery this is not as problematic, but the hay still needs to be dry to harvest and if it becomes ‘over-ripe’ it loses value, so there is still a fairly narrow time-window of opportunity – this is why you will see farmers with threshers and bailers working under floodlight until midnight on occasion at harvest time.

To our ancient ancestors this was a much bigger problem – a field of hay took days to cut and stack, the stooks then needed to ‘dry off’ before they could be brought in, so did you plant your hay to be ready to harvest at the beginning or the end of August? Or maybe it would be better to plant it to harvest at the beginning of September. Get it wrong and your animals could starve in the winter, or worse still your whole communities animals could starve.

To have a method that could predict what the weather was going to do in August or September could be life-saving. Rural folk have always had proverbs about weather patterns:-

  • Oak before Ash – In for a Splash, Ash before Oak – In for a Soak (Summer weather proverb)
  • Red Sky at Night, shepherds delight – Red Sky in Morning, shepherds warning (next day weather proverb)

This information has been gleaned from ‘weather watching’ over long periods of time and today quite a few of them are backed up with meteorological evidence – before this ‘Almanac’  were a ‘must buy’ – ‘Old Moore’s’ produced for the UK in Ireland and ‘The Farmers’ produced in the US – these provided all the information for the forthcoming year.

As Daryn Lehoux describes – our ancient ancestors had parapegma – the image of a section of the Coligny Calendar clearly shows the peg holes.