The Celtic Tree Calendar
There are thirteen moons in the Celtic Tree Calendar. Because the lunar cycle doesn’t line up perfectly with the solar calendar, exact dates cannot be given for the correspondence of the Tree Calendar with the commonly-used Gregorian, or Christian, calendar, which is solar in origin. This is because those dates are always changing relative to the solar calendar.
The Black Mountain Druid Order’s year of 13 moons is similar to the 13 moon lunar cycle observed by many non-Christian peoples throughout the world. Since our lunar calendar doesn’t align perfectly with the more common solar calendar, it takes approximately 19 years for the cycles to match up again.
The Greeks reconciled the solar year with the lunar year in something called the Metonic Cycle. Another Greek name for the Metonic Cycle is the Enneadecaeteris, which means “nineteen” in Greek, and the cycle is thus named because it takes approximately 19 years for the solar cycle and the lunar cycle to re-synchronize.
Coincidentally, Caesar stated in The Gallic Wars that Druids studied for 20 years, so if an ancient Druid served an apprenticeship for a year and a day, and then studied for 19 more years (or the period of one Metonic Cycle), he or she would have studied for a period of 20 years altogether before the Celtic lunar calendar re-aligned with the Roman solar calendar. So if, for example, a Dedicant began to study on the first full moon after the winter solstice, and studied for 19 years, then the next full moon after the winter solstice would be on the same day that the Dedicant began the path. It’s an interesting coincidence that this period of study so closely matched Caesar’s 20-year period.
The Tree Calendar consists of thirteen months named after trees. These trees also correspond to letters of the ogham alphabet described in more detail in future lessons.
The origins of the Celtic Tree Calendar are somewhat controversial. Robert Graves created the earliest known complete version in his book, The White Goddess. Graves claimed that his derivation of the Celtic Tree Calendar had its origins in ancient Druidic and Bardic traditions. He claimed to have uncovered a secret code hidden in the poetry and prose of the bards of the British Isles to demonstrate this claim.
Many scholars doubt this.
I prefer to think that the origins of the calendar are irrelevant as long as it has utility for us now. Many Pagans throughout the world use Graves’s version of the calendar today because of its elegance and utility, and our Order uses it for these reasons as well.
In the following section, the dates for each lunar tree month are approximate. In the Black Mountain Druid Order , we use 13 months of 28 days each to form our calendar. The first month, Birch Moon, begins with the day after the winter solstice. Each month thereafter begins 28 days later. To find your exact birth month, find the date of the winter solstice immediately preceding the date of your birth. The day immediately following the date of the winter solstice for that year would be the first day of the Birch month. 28 days after that would be the first day of the Rowan moon, and so on, in 28-day increments. There are 13 months in our calendar, each having 28 days each. This means 13 x 28 = 364 days. The final day, the winter solstice, is set apart as Mistletoe Day. In leap years, when there are 366 days there are two Mistletoe Days. But in ALL years, the day after the winter solstice is the beginning of Birch Moon.