Full Moon Names
Full Moon. Image courtesy of Tom Ruen.
In recent years it has become fashionable to assign names to the sequence of full moons which occur through the year. This practice has become especially common in North America, where it was popularised in the 20th century by the Maine Farmers' Almanac, which started printing such lists from the 1930s.
More recently, the source for many such lists is the Farmers' Almanac, which began producing such lists in the 1950s. Another early example of such a list was printed by Daniel Carter Beard in a Scout manual in 1918.
The names of the full moons are often said to have ancient origins from Native American tribes – a claim which has been examined in detail by Patricia Haddock's book Mysteries of the Moon (1992) and is partially true.
Here, we briefly summarise the history of these names.
Before the modern calendar came into universal use, many cultures used lunisolar calendars. Instead of having months of fixed lengths as in our modern calendar, a lunisolar calendar has months which are tied to the phases of the Moon. In such a calendar, each year lasts an average of 365.25 days – the period it takes for the Earth's seasons to repeat – but each month refers to the period from one new moon to the next – the period we now call a lunation. Each month thus lasts for an average of 29.5 days – the period of the Moon's phases – and the pattern of months differs from one year to the next.
The name lunisolar derives from the way in which these calendars depended on the cycles of both the Sun and the Moon.
Many cultures assigned various names to each of these months, often reflecting the changes in the natural world which take place at different times of years. These names were applied to the entire month, and not just to the full moon which occurred at the midpoint of that month.
The table below shows the series of month names listed by various sources, based upon ancient American and European traditions. All of these names have been translated into English from their original languages. The names listed by Daniel Carter Beard and the Farmers' Almanac are based on Native American traditions, though given the diversity of cultures this encompasses, it is unsurprising that the two lists differ considerably.
The Old English names are taken from the Venerable Bede's De temporum ratione (The Reckoning of Time; 725 AD) – an authoritative account of the calendar used in Saxon England. The Old German names are taken from the biography of Charlemagne (circa 817–833 AD), written a few years after his death.
|Old High German
|Moon after Yule
Bare spots on the ground
|Month of wildness
|Month of three milkings
|Month before midsummer
|Month after midsummer
|Winter Full Moon
|Month of sacrifice
|Moon before Yule
Naming months by season
Even aside from the issue that lists of Native American month names are usually medleys of names taken from many different cultures, it is a simplification to imply that ancient month names can be directly associated with our modern system of months.
The division of the year into months in a lunisolar calendar varies from year to year, depending on the phases of the Moon. In many cases, ancient cultures took the equinoxes and solstices as markers of the seasons, and assigned names to the sequence of lunar months falling within each season. So, in practice, the names listed above for July, August and September would have been applied to the first three full moons falling after the summer solstice.
Thus, while the table above lists the lunar month occurring in July as "the month after midsummer" according to Bede's Old English calendar, in practice this term would have been applied quite literally. It would have referred to the first month after the summer solstice.
Likewise, the North American "Wolf Moon" would have been the first lunar month after the December solstice, which might fall in either December or January.
In recent decades, the term blue moon has come to be given to a second full moon which falls within the same month as the previous full moon. This usage first appeared in the March 1946 issue of Sky & Telescope magazine. The magazine incorrectly stated that this was an established tradition which was already followed by the Farmers' Almanac. In fact, it was an entirely new usage of the term. However, the article became widely cited, and the term has since entered common usage.
It is possible for two full moons to fall within the same calendar month since the Moon's phases cycle, on average, 12.37 times each year. So once every 2.8 years, a single year contains 13 lunar months rather than the usual 12. In such a year, one of the months must have two full moons.
This awkward ratio of 12.37 arises because the Earth's seasons are determined by the period of the Earth's orbit around the Sun, while the Moon's phases are determined by the period of the Moon's orbit around the Earth. The periods of these two cycles are 365.25 days and 29.53 days respectively, and are unrelated to each other.
This awkward ratio has long been familiar to cultures which use lunar calendars, in which the months follow the phases of the Moon. Such calendars need the flexibility for some years to have 13 months rather than the usual 12, if the months are to remain sychronised with the Earth's seasons. Many cultures have devised elaborate procedures for deciding when a thirteenth month should be added into a year – called an intercalary month. Such months are routinely added into the Jewish calendar, though they are spurned by the Muslim lunar calendar.
The Venerable Bede mentions that in the Old English calendar this was done at midsummer, inserting an additional month called Þrilīþa (Third midsummer) after midsummer, once every 2.8 years.
The term blue moon appears to have been coined by the Maine Farmers' Almanac in the 1930s. In its efforts to recreate the calendars of Native American peoples, this almanac divided the year into four seasons, separated by the equinoxes and solstices, and used a list of three names for the full moons which fell within each season.
However, once every 2.8 years, one of these seasons would have four full moons rather than the usual three. The name blue moon was given to the third of these. The three traditional names were applied to the first, second, and fourth full moon falling within the allotted period. This custom appears to have originated with the Maine Farmers' Almanac in the 1930s, with no earlier precedent.
It was in their efforts to understand the procedure being followed by the Maine Farmers' Almanac that the writers of a 1946 article in Sky & Telescope magazine incorrectly concluded that the term was applied to a second full moon falling within a single calendar month.
Writer Joe Rao once speculated that the term blue moon might have medieval origins as a corruption of an earlier term, betrayer moon, since the Old English words for betrayer and blue are very similar: belæwe and belewe respectively. While this speculation has been often repeated, there is absolutely no evidence that the term predates the 20th century, or that either of these Old English words was ever used applied to the Moon. Even Rao himself described his theory as "completely wrong" in 2007.
Curiously, though, the phrase "once in a blue moon" is much older: it was first noted by the Oxford English Dictionary in 1824.
The Lenten Moon and the Harvest Moon
Three names, which have been used in England since at least the eighteenth century, follow their own special rules:
|The Lenten Moon is always the last full moon before the March equinox, since it always falls within lent.
|Many almanacs state that the name "harvest moon" is applied to the Moon nearest to the September equinox, which may fall in either September or October. The Oxford English Dictionary traces the term back to at least 1706.
|The Hunter's Moon is said to be the full moon which falls directly after the Harvest Moon. This may fall in either October or November. The Oxford English Dictionary traces the term back to at least 1710.
References – Beard, Daniel Carter; The American Boy's Book of Signs, Signals and Symbols (1918)
 – https://www.farmersalmanac.com/full-moon-dates-and-times
 – Bede; De temporum ratione (The Reckoning of Time) (725 AD)
 – Einhard; Vita Karoli Magni (Life of Charles the Great) (circa 817–833 AD)
 – https://www.space.com/3839-truth-month-blue-moon.html