A Note on the Dating of Beltane
Because the dating of the Celtic Beltane festival can be confusing to the general public, the following explanation is offered.
Beltane (the Celtic May Day known in Ireland as “Old May”) is a mid-Spring seasonal festival welcoming in the summer. It is celebrated (in the Northern Hemisphere) on the eve of May 1st (since the Celts marked the new day at sunset). This has become, in the modern period, the customary date on which Beltane begins. However, this festival date (like the other three “cross-quarter” festival dates on the four-spoked “Celtic Wheel of the Year”) is not a precise date on our solar calendar. This has to do with calendrical changes; (a) the change from the Julian calendar to the Gregorian calendar and (b) the Celtic use of a lunisolar calendar. Thus, the dates of the festival are different depending on which Celtic country it's celebrated in. For example, in Ireland Beltane began the evening of the 11th of May, while Scotland it was commonly celebrated on the 15th of May. Before the use of calendars, it is said that many Paleo-Celtic peoples celebrated Beltane when the first pinky-white blossoms of the sacred hawthorn tree (also known as “the May”) blossomed during this month in Ireland and the British Isles.
Again, these different calendar dates marking the time of Beltane are due to various calendrical changes down through the centuries. However, besides the “Fixed Date” on the calendar (“Calendar Beltane”), there is a second method of dating, which is the “Astrological Date” and is called “True Beltane,” because it’s astronomically accurate. Thus, the calendar date of Beltane is not the same as its astrological date. Beltane in this astrological calculation occurs when the Sun is at 15° Taurus, the exact astronomical midpoint between the Spring Equinox and Summer Solstice, or the full moon nearest this point. (This means that Beltane is not just a day in duration, because in astrology a date is never just a date but a degree of the Zodiac. Thus, the celebration of Beltane was not traditionally just one day, as it is now customarily celebrated. Historically, in many locales the celebration of either Beltane or May Day lasted anywhere from a few days to a couple of weeks and, it some locales, an entire month, thus the famous British appellation: “The Merrie, Merrie Month of May.”) Hence, the “True Beltane” falls around May 4th eve and May 5th, but even this can vary from year to year. (It should be mentioned that there is also “Astronomical Beltane,” which occurs when the constellation Pleiades can be seen on the dawn horizon. It is said that the ancient Celts, who were well-versed in astronomy, would have been aware of changes to the stars that heralded a change in seasons. Thus, they knew the time of Beltane was near when they saw the rising of the constellation Pleiades on the dawn horizon. The Pleiades are also known as the Seven Sisters and the first born and most beautiful of the Sisters is named “Maia,” from whom the month of May is named.)
That said, trying to pin down the “real” date of when the ancient Celts celebrated Beltane is impossible. However, since the Celtic year was based on both lunar and solar cycles (a lunisolar calendar), it is possible that the holiday was celebrated on the full moon nearest the midpoint between the Spring Equinox and the Summer Solstice; i.e., the full moon of Taurus as it passes through Scorpio. (The first full moon in May is called “Lunar Beltane.”) This astrological date has long been considered a “power point” of the Zodiac. Again, this date, like all astrologically determined dates, may vary by a day or two depending on the year. However, it may be calculated by determining the date on which the sun is at 15° Taurus, usually around May 5th. Therefore, astrologically calculated, Beltane occurs in the mid-point of Taurus, when the Sun reaches 15° degrees Taurus. (It should be pointed out that the “Fixed Date” was a later development in calculating when to celebrate Beltane. The early Celts used their Coligney calendar, a lunisolar calendar, which was different from our Gregorian calendar. Prior to this, because of the change from the Roman Julian to the Gregorian calendar, Beltane fell on May 13th or 14th. Actually, there is nothing astronomically significant about the May 1st date, nor was it significant to the ancient Celts, since it’s based on the Gregorian calendar which was only invented in 1582 CE., when Pope Gregory XIII moved the date backwards by 11 days in most European countries. Overnight, May 12th became May 1st. To add to the complication of the dating of Beltane, England and America did not adopt the Gregorian calendar until 1752. Furthermore, in Medieval and Renaissance times, these Beltane celebrations took place 11 to 15 days later in the season, at a time when the weather was noticeably warmer, dryer, and when many more spring flowers bloomed.)
Concerning the astrological dating of Beltane (“True Beltane,” May 4th or 5th) Celtic folklorists call it Beltane O.S. for “Old Style” and neopagan Wiccans often refer to this date as “Old Beltane.” (The neopagan or Wiccan calendar is closely intertwined with astrology.) However, within the neopagan community there are different schools of thought about when exactly Beltane is supposed to be celebrated. Furthermore, even if there were general agreement on the “Fixed Date“ of May 1st, discrepancies in the actual time of celebration arise because of convenience only. Hence, one can find this or that neopagan group celebrating on a weekend before or after May 1st, if Beltane falls on a weekday.