It’s Halloween, Full Moon and a Blue Moon – but what does that mean? by Professor Anne Lawrence-Mathers

It is very hard to miss the fact that Saturday 31st October is Halloween, and that this year the date coincides with a full Moon.  Still more unusually this full Moon will be acclaimed as a ‘Blue Moon’ since it is the second to fall in the same month (the previous one being Thursday 1 October).  This is a very rare combination since Halloween falls at full Moons only roughly every twenty years (the last occasion was 2001 and the next will be 2039).  Blue Moons are also scarce, with the most recent one being March 21st 2018.  However, Blue Moons can also be the third of four full moons to occur in a single season.  Here a season is the period between a solar solstice and equinox. The next ‘seasonal’ Blue Moon will be August 22, 2021.  All this may suggest that Halloween has a special relationship to both the solar and the lunar calendars – but in fact that is very hard to prove.

The name Halloween itself has nothing to do with the Sun or the Moon, since it is simply a contraction of All Hallows Eve.  This derives from the fact that Halloween is the evening and night before the Christian festival of All Hallows, or All Saints.  That festival was placed on 1st November from the eighth century onwards and therefore Halloween fell on 31st October.  What is much less clear is why this pair of dates was chosen.  In the early middle ages a feast day celebrating all martyrs was held soon after Easter, and from the seventh century was replaced by a date in May, originating in Rome.  This fell close to, though not at, the pagan Irish feast of Beltane, whilst the new date for All Saints coincided with the date of Samhain, the feast marking the onset of Winter.  Since the new timing was first recorded in Anglo Saxon England, where the Venerable Bede was working hard to reduce the influence of Celtic Christianity on matters such as the date of Easter, it is worth looking at the information Bede offers.

Bede noted that the pagan Anglo Saxons called October ‘Winter fills’ and November ‘Blood Month’.  He regarded the first as self-explanatory but explained that the blood spilt in November was that of cattle, slaughtered before the onset of winter and dedicated to pagan gods in unspecified rituals.  Therefore, if Bede’s evidence about Anglo-Saxon paganism is put together with surviving information about Samhain then the night between October and November emerges as one in need of purging of pagan significance.  Like Beltane, it also falls at a point midway between two key points in the solar calendar.  While Beltane falls between the Spring equinox and the Summer solstice, Samhain – and thus Halloween – falls midway between the Autumn equinox and the Winter solstice.  This makes Halloween, like Mayday, a seasonal festival as well as one located at a transitional point of the solar year.

However, none of this links Halloween to the full Moon – or even the lunar calendar.  The astronomical event which falls at Halloween is (or more accurately used to be) the midnight culmination (or highest point in the sky) of the star cluster of the Pleiades.  In the medieval period this took place at the start of November; and Roman writers had emphasised the importance of the Pleiades in marking the transition of the seasons.

                                                                             ©British Library, Ms Harley 647, f4v.

What links Halloween most strongly to the Moon is their shared association with beliefs about the supernatural and about foretelling the future.  Traditions about using the lunar calendar to make predictions about coming events were passed from the classical world to medieval Europe and were accepted by the Christian Church.  Prognostic texts known as Lunaries gave the necessary information and were copied into manuscripts containing both medical and liturgical information.  The day and night of the full Moon were propitious times for starting new phases of life, such as getting married or going to school or university.  But these predictions worked for any lunar month, not only the one containing Halloween!

This takes the enquiry back to the shared theme of the supernatural, and to ghosts and witches in particular.  From the early middle ages there were fears that ghosts and spirits were able to return to earth and do harm to people, animals and crops, at liminal times – and at Halloween in particular.  This made the lighting of fires and candles, and the protective ringing of church bells, important on this night.  Gifts of food were also offered, either directly to the souls of the dead or as alms in exchange for prayers.  By the sixteenth century an additional supernatural threat had been added to the perils of the night, as growing fears about witches led to beliefs that witches were especially powerful and likely to cause harm on that night.  The medieval idea that witches were both in league with the devil and worshippers of the pagan deity, Diana, goddess of the Moon, perhaps provides the final link in this long chain of associations.

The memorably named Burchard of Worms compiled his Corrector in the early eleventh century and it included a text which was to be very influential.  This banned pagan traditions relating to the worship of the Moon and to rituals at new Moon and lunar eclipses. It went on to condemn those who believed that ‘the witch, Hulda’ rode on the backs of animals on special nights (which are not named) together with a throng of demons disguised as women.  Equally outlawed were the women who believed that they flew at night on the backs of animals, riding with Diana, swooping around the world and obeying the demonic commands of the goddess.  The text does not state whether Halloween was one of these special nights, nor whether a full Moon made the goddess and her followers especially powerful, although it is open to that interpretation.  But its terrifying details played a major part in the development of medieval and early modern ideas about witches.  When combined with the Christian idea that the period from Halloween to All Souls (also known as Hallowmass) was crucial for maintaining a positive relationship between the living and the dead it helps to explain the power of the night between 31st October and 1st November, and why a full Moon might be significant. 

You can find out more about Professor Anne Lawrence-Mathers and her work at the university of Reading here

Anne was a guest on BBC Radio Berkshire on Friday 30th October discussing Halloween!

Her book Medieval Meteorology argues that there was significant ongoing study of meteorology and weather in the early middle ages.

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