The original version of this calendar had a year of 25 months and mean month exactly equal to the mean month of the Yerm Lunar Calendar. One cycle (of 204 lunar years) was equal to six cycles of the Yerm Lunar Calendar.
Peter Meyer was not happy with a mean lunar year not equal to a solar year, so in February 1998, he published a new version of the Goddess Lunar Calendar where each year has either 12 or 13 months and the mean year is very close to a tropical year in duration. However the new year does slowly wander back and forth through all the seasons over its 1689-year cycle. The intercalation is governed by the digit total of the year number in the 1689-year cycle.
Peter has subsequently replaced this with a calendar that has a 13-month year as described below.
Terence McKenna's Goddess Calendar
Most "Goddess Calendars" that you can find on the web are actually just the usual Gregorian Calendar with the twelve months renamed after goddesses, so they are not really new calendars — and they are solar calendars , not lunar calendars. This page defines an accurate 13-month lunar calendar in which the months actually do coincide with the lunar cycles. It is based on a proposal for a new calendar made by Terence McKenna in 1987 but has been given its final form only recently.
In The Invisible Landscape Terence McKenna cited a scholar who suggested that the I Ching hexagrams were connected with some early calendar system (see the 1975 edition, Chapter 8, pages 113-114). He then proceeded to speculate that the neolithic Chinese used a lunar calendar in which a year of 384 days consisted of 13 lunar months (alternating in length between 29 days and 30 days). Here are the relevant sections from pages 113 and 114 of The Invisible Landscape: The fact which is of central interest is the coincidence of the duration of thirteen lunations and the number 384. The true value for the duration of a lunation is 29.530588 days. Examination of oracle bones dated to the -13th century has, according to Needham, led to the conclusion that at time the length of the lunation was known to 29.53 days.
- 29.53 days × 13 = 383.89 days
The nearness of this number to 384 is made significant when one realizes that 384 is the number that arises when 64 is mulitiplied by 6, 6 being the number of yao or lines in a single hexagram. This last sentence introduces one of the assumptions by which we will advance the argument. It is the assumption of hierarchical or resonance thinking in Chinese intellectual constructs. In this case, it is the notion that what is done with the yao, the most basic element of a hexagram (multiplication by 6 to form a hexagram), might also be done with the entire set yao, the complete sequence of 64 hexagrams. This idea that operations carried out on one level are elegant and efficacious if carried out in a similar way on other levels is intimately related to our second premise. This is the idea of cyclical recurrence of events and situations on many different scales of duration.
It is established, therefore, that striking correlations exist between a count of 6 × 64 days and lunar motion. The 384-day year is a lunar year of 13 months. Such a lunar year has been determined to be 383.9 days or 0.1 day less than 384 days. Therefore, the cycle loses 2.4 hours (0.1 day) each 384 days. If one were to adopt 384-days long as a calendar and insert one intercalary day every 10 of such years, making every 10th year 385 days long, this calendar would lose one day every 454.5 of its years. Thus, the calendar would be accurate to .0022 day loss per 384-day year. This is accurate indeed as calendars go.
That neolithic calendars in China where lunar is generally regarded as established. The two most likely year counts would necessarily be 384 days (13 lunations) or 354 days (12 lunations). Three hundred eighty-four, if used as a day count, seems to have resonances with the durations of other astronomical cycles of longer duration. To demonstrate these resonances, it is necessary to continue to apply the same principles of hierarchical extrapolation that link the 64 hexagrams to a duration of 384; that is, multiplication of subunits into larger modules via numbers inherent the structure of the I Ching: 6 or 64. We suggest that the 384-day lunar year discussed above was viewed by the calendar makers of early China as a hexagram. This idea would have arisen as a natural consequence of observing the relationships between the 6 yao of the hexagram and the 6 small cycles of 64 days each of which together formed the 384-day year.
In a talk entitled "A Calendar for the Goddess" given by Terence McKenna on October 3, 1987, at Shared Visions Community Center in Berkeley (available on tape from Sound Photosynthesis) he put forward a proposal for a new calendar similar to the one allegedly used by the neolithic Chinese. In this calendar there are thirteen months in a year, the odd-numbered months having 30 days and the even-numbered months having 29 days, for a total of 384 days in a calendar year (this is not a solar year of 365 or 366 days as in the commonly-used calendar). Thus the average length of each month would be 384/13 = 29.538 days, which is somewhat in the neighborhood of the length of the mean lunar month, 29.531 days. The names of the months, he suggested, could be the same as in the present Gregorian calendar except that there would be an extra month called "Remember" between August and September (so as to remind us to remember the Goddess).
One of the virtues of this calendar, according to its author, would be that it would help to free us from "solar paternalism", subservience to the myth of the solar deity (originally the Roman Emperor, now his successor, the holder of the office of President, Chancellor, etc., chief executive of the modern bureaucratic patriarchal nation state). The solar deity ruled over a static ordering of time in which everything, from the seasons down, had its fixed and allotted place. A calendar in which the months are no longer fixed to the seasons might allow for a less bureaucratic way of thinking among its users.
An accurate lunar calendar, however, is not constructed as easily as one might suppose. The main property that a lunar calendar should possess is that the calendar months stay in sync with the phases of the moon over a long period of time. If we simply used a year of thirteen calendrical months alternating in lengths of 30, 29, 30, 29 etc., days then (as Terence says in The Invisible Landscape shown above) a calendar year, consisting of 384 days, would differ from thirteen mean lunar months by an average of about 0.1 days, since 13 times 29.531 days = 383.903 days. Thus after ten of these 13-month years the calendar would be out of sync with the lunar cycle by about one day, and after 70 years, when the calendar said there was full moon in the sky there would actually be a half moon.
Thus some correction to the basic scheme of alternating 30- and 29-day months is needed in order that the new moon (or the full moon) should always occur on (or at least close to) the first day of the calendrical month. In The Invisible Landscape (page 114) it is suggested that a leap day be inserted every ten 384-day years, "making every 10th year 385 days long". Actually it is necessary to remove a day rather than to add one. Not removing (or adding) any day would make the average length of a calendar month to be (10 × 384 - 1) / (10 × 13) = 29.53077 days, or 0.00018 days more than the current true length of 29.53059 days. Thus after about 5555 calendar months (1/0.00018), or about 450 solar years, this calendar would be out of sync with the lunar cycle by about one day.
While this accuracy is not too bad, it is not particularly good, and is insufficient for a calendar which is intended to remain accurate over a period of several thousand years, so a further correction is needed.
The McKenna-Meyer Goddess Calendar
This calendar is named after Terence McKenna who originally proposed an early version as described above, and Peter Meyer, who (in May 2012) formulated the improved version defined here (first published 2012-06-07). It can be referred to as "the Goddess Calendar" for short.
This calendar partitions the empirical sequence of days-and-nights ('days' for short, though the technical term is nychthemeron) into months, years and cycles. A nychthemeron begins at midnight local time. All months have either 29 days or 30 days, numbered '1' to '30'. Every year has exactly thirteen months, '1' to '13'.
Every cycle has exactly 470 years, numbered '1' to '470'. Cycles are numbered by the integers: ..., -2, -1, 0, 1, 2, ... (This calendar is intended mainly for use with current dates rather than for recording dates of all past events, since that can be done as now with the Common Era Calendar, which is the same as the Gregorian Calendar today, so dates with cycle numbers which are zero or negative are theoretically possible but are not intended to be used.)
Odd-numbered months have 30 days and even-numbered months have 29 days except that in a year whose number is divisible by 10 or by 235 (or by both) the 13th month has just 29 days. (Such a year is termed a short year.)
A date in this calendar is written as cycle-year-month-day, with 'MMG' appended to show that this is a date in this calendar. Thus the first day of the first month of the first year of the first cycle is 1-1-1-1 MMG, and the last day of the last month of year 101 of the second cycle is 2-101-13-30 MMG. For dates in the first cycle, the leading '1' can be dropped, so then dates are of the form year-month-day.
In a lunar calendar intended as a way of disengaging from the currently-used solar calendar it is not advisable to take over the month names used in that calendar ("January", "February", etc.), and a calendar which is "for the Goddess" does better to name the months after goddesses, such as the following (see the Thirteen Goddesses):
This calendar is related to the sequence of empirical days by identifying the date 1-1-1-1 MMG with the date 1901-08-14 CE. In other words, Athena 1 in the year 1 in the McKenna-Meyer Goddess Calendar corresponds to August 14 in the year 1901 in the Common Era Calendar. On this date a dark moon occurred at 8:27 GMT (and there also occurred the first manned, powered, controlled, heavier-than-air flight). This establishes a one-to-one correspondence between dates in the two calendars and makes possible conversion of any date in one of them to a specific date in the other.
While not part of the definition of this calendar, the present system of 7-day weeks (which has almost no relation to the lunar cycle) may be used concurrently, just as now done with the Common Era Calendar. Also a nychthemeron in this calendar may be divided into hours and minutes according to the present custom, with '00:00' denoting local midnight.
Average Length of a Month in the Goddess Calendar
This calendar is a lunar calendar whose months are intended to stay in sync with the cycles of the moon, a.k.a. lunations. A lunation runs from the time of the dark moon (the moment when the Moon, in its orbit around the Earth, is in exactly the same direction as the Sun). The time of a lunation is not constant, but varies slightly from one lunation to the next. The average time of a lunation is known as the synodic month. The present value of the synodic month is 29.530588 mean solar days.
So what is the average length of a calendar month in the McKenna-Meyer Goddess Calendar? The pattern of month lengths is repeated every 470 calendar years, so the average length of a month is the number of days in 470 years divided by the number of months in 470 years.
A year whose number is not divisible by 10 or by 235 is called a normal year; otherwise it is a short year. A normal year has 384 days and a short year has 383 days. In years 1 through 470 there are 47 years divisible by 10 and there are two years divisible by 235, namely, years 235 and 470. Year 470 is divisible both by 10 and by 235, so there are 47 + 1 = 48 short years, each with 383 days. The other 422 years are normal years, each with 384 days. So the total number of days in 470 years is 48*383 + 422*384 = 180,432 days. Since the number of months in 470 years is 13*470 = 6,110, the average length of a month is 180,432/6,110 = 29.5306056 days.
This differs from the current value of the synodic month by 0.0000168 days, so (assuming no change in the value of the synodic month) it will take about 1/0.0000168 = 59,523 months (about 4,579 calendar years, or about 4813 solar years) before the calendar is out of sync with the lunar cycle by one day. Thus this is an accurate lunar calendar in the sense that months remain in sync with lunations.
Other Properties of the Goddess Calendar
The average length of a solar year (measured from the vernal equinox) is 365.2424 days. The average length of a calendar year is 180,432/470 = 383.89787 days so New Years Day in this calendar moves forward in the seasons by 18 or 19 days each year, completing a cycle in approximately 19.58 solar years.
As stated above, in 470 calendar years there are 6,110 months, almost exactly equal to 26 Metonic cycles (each of which consists of 235 lunations).
A period of 18 calendar years lasts on average 6910.162 days, equal to 18.919 solar years. A period of 18 calendar years plus one calendar month lasts on average 6939.69 days, which is almost exactly 19 solar years and is almost exactly one Metonic cycle.
In 470 calendar years there are exactly 180,432/7 = 25,776 7-day weeks.
Due to the irregularity of the Moon's orbit, dark moons and full moons can never occur on fixed days in a rule-based lunar calendar. For the 470 MMG calendar years in cycle 1 (August 1901 CE to August 2395 CE) a full moon always occurs on the 14th, 15th, 16th or 17th of the calendar month, and a dark moon always occurs on the 1st, 2nd, 29th or 30th of the calendar month.
Conversion between Goddess Calendar Dates and Common Era Calendar Dates
The page The Goddess Calendar for Year... displays all months in the Goddess Calendar for the current year and for any selected year (1 through 470 in cycle 1). It also shows the full moon date in each month. A date is a full moon date if the exact time of the full moon occurs on that day after 12:00 or on the next day before 12:00. Full moon parties are best held on a full moon date. Full moon dates depend on timezone, because the time of the exact full moon differs in different timezones. That page allows you to choose between GMT and your local timezone.
To discover which goddess is associated with the month in the Goddess Calendar in which you were born go to Find Your Goddess from your birthdate.
You can print out a wall-calendar-type page for a single month at a printable month in the goddess calendar. This can be used as a planner. You could even print all 13 months for a year and bind them.
There is a Windows program which converts between Goddess Calendar dates (in any cycle, not just cycle 1) and dates in the Common Era Calendar, and also dates in four other lunar calendars — see Lunar calendar.
The CD-ROM contains a Windows program for Goddess Calendar date conversion. To install it, locate (in Windows Explorer) the file mmgc_setup.exe in the folder mmgc\exe. Click on the file name or the program icon to run the installation program, then follow the prompts.
- Goddess Lunar Calendar This gives the complete rules of the present version of the Goddess Lunar Calendar.
- The 13 Goddesses of the Goddess Calendar
- Old Goddess Lunar Calendar This shows how the original Goddess Lunar Calendar relates to the yerm lunar calendar
- Goddess Lunar Calendar of 1998
- Lunar Calendars and Eclipse Finder finds dates of solar eclipses, lunar eclipses and moon phases, and converts dates in several lunar calendars