The Irish Calendar

And then the moon, like to a silver bow New-bent in heaven, shall behold the night of our solemnities. 

— Willam Shakespeare, A Midsummer Night’s Dream

We recently explored the differences between the typical, astronomical reckoning of seasons and the meteorological method. The former employs celestial geometry cues, while the latter depends on average temperatures. Sound logic underpins both methods, and they both feature situational benefits.

But orbital tilt, angles, hot, and cold are not the only ways we might demarcate seasons.

In Ireland, vestiges of an ancient calendar persist in festivals and practices, a calendar based on another criterion: sunlight.

Titania, Queen of the Fairies, sleeping in the moonlight by John Simmons

The summer solstice, which typically occurs around 20 June, marks the beginning of astronomical summer. This borderline makes a lot of binary sense: before the solstice, days lengthen as Earth tilts toward the sun; after the solstice, days shorten as Earth tilts away from the sun. We associate summer with the hottest and brightest parts of the year. Both astronomical and meteorological summer do a good job of approximating this period. However, one thing that often causes consternation among those who worry about such things is astronomical summer inherently provides less daylight with each passing day. Something psychologically dissonant accompanies the mixing of “summer” with “lessening light.” Summer should provide the most light!

If you agree with the previous sentiment, the Irish have you covered.

The Irish Calendar eschews axial tilt and average temperature, instead focusing on insolation. This Scholastic Aptitude Test word means the amount of sun an area receives. So, in the Irish Calendar, seasons are defined by the amount of light they receive.

Cue Shakespeare.

A Midsummer Night’s Dream transpires near the summer solstice. The title, however, pegs this as midsummer. In a calendar based on insolation, the summer solstice marks the middle of summer, not the beginning. Summer becomes the quarter of the year with the most sunlight. Winter, by contrast, is the quarter with the least sunlight. Spring and autumn fall in the portions betwixt the two.

Diagram comparing the Celtic, astronomical and meteorological calendars - graphic by Ccferrie

Before the formalization of the Julian and Gregorian calendars, many civilizations reckoned seasons in this manner, but, after the medieval period, most people moved away from this method. Irish tradition maintained the practice.

Solar seasons change on so-called “cross-quarter days.” The quarter days represent the solstices and the equinoxes. Cross-quarter days occur on the points halfway between each of the astronomical events. In Ireland, these days maintain proper names. The first day of spring is Imbolc, which happens on 1 February; summer begins on 1 May with Beltane; autumn dawns on Lughnasadh (sometimes Lunasa), which is 1 August; finally, Samhain – the Irish name for November and the origin of Halloween – kickstarts winter on 1 November. On these days, people celebrated important milestones, such as the end of the harvest or the rebirth of nature. The Irish word for autumn – Fómhar – means “harvest.” Samhain marked the end of the harvest and the beginning of the darker half of the year, a period symbolized by death. It’s no coincidence that Halloween, All Saints’ Day, and All Souls’ Day fall near this cross-quarter day!

On the Irish Calendar, the seasons break down like so:

Winter = November, December, January
Spring = February, March, April
Summer = May, June, July
Fall = August, September, October

Ancient Celts provided monikers for the important astronomical dates, too. You might recognize Yule, the name for the winter solstice, but Litha (summer solstice), Ostara (spring equinox), and Mabon (autumn equinox) have not remained as ingrained in today’s nomenclature. 

A bit of quick math will illuminate to the intrepid reader that Litha (midsummer) is not equidistant between Beltane and Lughnasadh/Lunasa. Today, the Irish calendar begins its seasons on the first of the respective months, but these dates do not shake out to match insolation. The festivals to commemorate the new seasons were not celebrated on the same day each year. Instead, an approximate observation probably mirrored the lunar cycle in the vicinity of the actual solar cusps. We’ve discussed before the havoc the moon caused our ancestors, who wanted to base months upon our satellite. More than 12 but fewer than 13 lunar cycles occur in the average year, which does not produce neat calendars. So, the moon didn’t always arrive at the same time when the Earth reached a yearly point in its orbital cycle. Further, the solar reckoning certainly predates the current Gregorian calendar and even the older Julian. Those systems have achieved hegemony, however, and, at some point, pegging the “official” start to seasons on the Irish Calendar probably made some sense. The drawback to a neat genesis on the first of a month is the non-mathematical sharpness of insolation in those seasons.

The annual cycle of insolation for the northern hemisphere - graphic by Invent2HelpAll

The graphic above illustrates the interplay between these reckoning systems. The blue line is solar energy, which powers the Irish Calendar. The pink line is temperature, which displays seasonal lag, forming the basis of meteorological seasons. The letters on the bottom are months on the Gregorian calendar, beginning in March. On the bottom are the cross-quarter days, the start of Irish seasons, while the top lists the solstices and equinoxes. Astronomical seasons are labeled, which allows one to visualize the peak insolation that comes with Irish summer, splitting astronomical spring and summer.

In many mythologies, supernatural hijinks about near the summer solstice, making midsummer a fitting setting for Shakespeare’s dreamy, time-bending play. Working through the distinctions between seasonal systems is enough to make anyone feel like the victim of a puckish faerie.

Which design makes the most sense to you? I must admit, the Irish notion might stand out to my sensibilities. I enjoy the warm temperatures of summer, but, if I truly examine what the season does for me, it’s the daylight that stands out. Cooler temperatures can persist, as long as the day is long. Matching summer to the longest portion of the year resonates with the ancient Celt within.

Further Reading and Exploration

When do seasons start and end? – Lee Valley Ireland

Ancient Celtic Calendar: Quarter Days and Cross-Quarter Days – Almanac

Wheel of the Year – Celtic Journey

Insolation – University of Calgary

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