Blue Moon - Moon Phases - The White Goddess

Blue Moon

"Once in a Blue Moon ..."

'Thirteen silver moons in a year are,
Thirteen is the coven's array.
Thirteen times at Esbat make merry,
For each golden year and a day.'

The Lunar Month

The Moon, the closest astral body to the Earth, revolves around the Earth 13 times a year.  The lunar month, is the period of one revolution of the moon.  According to Brewer's Dictionary of Phrase and Fable, Millennium Edition, a month is one of the 12 divisions of a year, and a new month would start on the day of the new moon. The Old English word mõnath, is thought to mean month.

It is also worth pointing out that the word fortnight (from the Middle English fourtenight, alteration of fourtene night, fourteen nights and Old English fowertne, fourteen + Old English niht, night) is a period of fouteen nights, and a further indication of the use of a lunar calendar in precedence of a solar one. (The word sennight, means seven nights or one week.)

There are several methods of calculating the length of a lunar month.

The Synodical Month, or period from one new moon to the next, in mean length 29 d. 12 h. 44 m. 2.87 s.

The Nodical Month, or time of revolution from one node to the same again, in length 27 d. 5 h. 5 m. 36 s.

The Sidereal, or time of revolution from a star to the same again, equal to 27 d. 7 h. 43 m. 11.5 s.

The Anomalistic, or time of revolution from perigee to perigee again, in length 27 d. 13 h. 18 m. 37.4 s.

The Tropical, or time of passing from any point of the ecliptic to the same again, equal to 27 d. 7 h. 43 m. 4.7 s.

Solar month, the time in which the sun passes through one sign of the zodiac, in mean length 30 d. 10 h. 29 m. 4.1 s.

So a month can be thought of as the time taken for the moon to revolve around the earth, or 29.5 days, so a Lunar Year would be 354.5 (29.5 x 12) days approximately. The mean length of the lunar month lasts 28 days, which if you multiply by 13 gives you 364, 1 day short of a calendar year. Or the proverbial, witches year and a day.

What exactly is a Blue Moon?

There are several definitions of a Blue Moon.  The term 'Once in a blue moon' has come to mean something that occurs very infrequently.

The Pears Encyclopaedia definition is of a phenomenon caused by the scattering of sunlight in transparent particles suspended in the atmosphere. The dust from Krakatoa eruption in 1883 and the forest fires in Alberta, Canada in 1950 gave rise to 'Blue Moons and Suns'.

Philip Hiscock in his research states that the term "Blue Moon" has been around a long time, well over 400 years and that its usage was akin to saying "He'd argue that black is white" and was an obvious absurdity.
(For more information see Blue Moon or Once in a Blue Moon)

The Calendrical Blue Moon.

The average interval between Full Moons is about 29.5 days, whilst unlikely that any given month will contain two Full Moons, it does happen. For every one hundred years, there will be approximately 44 'calendrical Blue Moons' or one every two and half years. So a Blue Moon, by recent popular folklore comes to mean the second Full Moon in a single calendar month.

Maine Farmers' Almanac

When the Gregorian calendar reforms were introduced in 1582, the following calendar months, where adjusted; April, June, September, and November, containing 30 days, and the rest 31, except February, which, in common years, has 28, and in leap years 29. This Gregorian calendar is based upon a twelve part division of a circle, and has become, over the last 400 years the official civil calendar worldwide.

The Maine farmers Almanac, uses Seasonal Moon names in accordance with the ecclesiastical rules for determining the dates of Easter and Lent. The beginnings of summer, fall, and winter are determined by the dynamical mean Sun. When a season contains four full Moons, the third is called a Blue Moon because only then will the names of the other full Moons, such as the Moon Before Yule and the Moon After Yule, fall at the proper times relative to the solstices and equinoxes.

So Which is the correct definition?

The Calendrical Blue Moon meaning the second Full Moon in a single calendar month, is a fairly modern definition and is probably no more than 20 to 30 years old. The ecclesiastical rule, is based on the 1582 Gregorian calendar reforms, and because these blue moons are based on a calendar method, it has to be suspected of manipulation to fit within certain set rules.

Blue Moon or Not Blue Moon

If, the ancients measured time using a Lunar Cycle as opposed to a Solar Cycle; then the astronomical peculiarity known as a 'Blue Moon', whether measured by Ecclesiastical rules or modern folklore as 2 full moons in a (solar) calendar month, would never have occurred. So, where does that leave us, in regard to the origin of the Blue Moon? For me, the only other explanation is of a physical phenomenon that caused the moon to appear blue to observers from earth.

It is my belief that these visible blue moons gave rise to the folk sayings such as "He would argue the Moon was blue", and term 'Blue Moon', was later used to denote the extra moon, which didn't have a seasonal name, within the ecclesiastical rules for determining the dates of Easter.