Little Almanac

Cross-Quarter Days

A cross-quarter day falls between a solstice and an equinox. Four of them open the seasons of the Gaelic year, and they carry the four best-known festival names in the modern ritual calendar. Where exactly they fall has three answers, all defensible, differing by up to a week. This site computes all three and does not choose between them.

The three datings

The calendar date. Samhain on 1 November, Imbolc on 1 February, Beltane on 1 May, Lughnasadh on 1 August, or the evening before each, since day-reckoning that begins at sunset makes the eve the opening of the festival rather than a vigil before it 1. These are the dates in the medieval Irish material 2 and in every later folk record, and they are the dates most modern practice keeps.

The solar-longitude midpoint. The instant at which the Sun reaches ecliptic longitude 315°, 45°, 135° or 225°, which is the exact angular halfway point between a solstice and the adjacent equinox 3. In the present era these fall several days after the calendar dates: around 3 to 4 February, 5 to 6 May, 6 to 8 August, and 6 to 8 November.

The temporal midpoint. The instant exactly halfway in time between the solstice instant and the equinox instant. This differs from the angular midpoint, because the Sun does not travel along the ecliptic at a constant rate.

Why the three disagree

Three separate causes, and they push in different directions.

The calendar dates were fixed under the Julian reckoning and never moved. The Julian year of 365.25 days runs about three days long per four centuries against the tropical year. By 1582 the accumulated error stood at ten days, and the Gregorian reform removed it by realigning the calendar to the equinox as it had stood at the Council of Nicaea in 325 4. Dates fixed to the calendar before the reform, and carried through it unchanged, therefore sit at a different point in the solar year than they did when they were set.

The Earth’s orbit is eccentric. Perihelion currently falls in early January, so the Sun’s apparent motion along the ecliptic is fastest in the northern winter. The winter half-year from the September equinox to the March equinox runs about 179 days; the summer half runs about 186. The seasons are not equal in length, so their midpoints are not symmetrically placed 3.

“Halfway” has two meanings. Halfway in angle and halfway in time are the same thing only for uniform motion, and the Sun’s apparent motion is not uniform. The two definitions give instants a few hours to a day or so apart, depending on the station and the year. Neither is a better definition of a midpoint than the other; they answer slightly different questions about what a season’s middle is.

Correction

Commonly saidThe astronomical cross-quarter is the real date, and 1 November is a Christian corruption of it.

The calendar date has the better claim to being the historical one. The four quarter-days appear in medieval Irish literature attached to calendar dates, and the whole recorded body of custom, from the Scottish and Irish fire ceremonies to the harvest assemblies, is attached to the calendar dates as well 1. No medieval Irish or Welsh source describes reckoning a festival from the Sun’s position between a solstice and an equinox. The astronomical midpoints are a modern refinement, available because the computation is now cheap, and that is their justification.

There is more to add. The clean grid of first-of-the-month dates is itself a medieval regularisation. In a lunisolar system, which is what the surviving Gaulish calendar evidence attests for at least one Celtic-speaking region, festival dates move against the solar year and cannot be fixed to a Julian date at all 5. So the choice is between two regularisations, one made in the Middle Ages and one available now, of something that was probably never fixed in the first place. See The Coligny Calendar.

What this site does with them

Each of the four stations is shown with all three instants side by side, each translated into the local date and time of the requested place, together with the offset between them in days. Presenting one figure would require choosing, and the choice is not the site’s to make: a household that keeps 1 November and a household that keeps the 225° instant are both doing something with a defence.

The four entries for the stations themselves treat what the medieval sources attest at each: Samhain, Imbolc, Beltane and Lughnasadh. For the astronomy of the solstices and equinoxes these are measured from, see Solstices and Equinoxes.

Gap in the evidence

Why the four fall where they do is not settled. They open the seasons of a pastoral and agricultural year, and the dairying and herding rhythms of Ireland account for the shape of that year well enough. Whether anything astronomical contributed is another matter. The Pleiades set heliacally in early November and rise heliacally in early May at Mediterranean latitudes, which is the pair of events that anchors the agricultural year in the earliest European star-calendar text, and the coincidence with the early-November and early-May stations is striking. It is also nothing more than a coincidence so far: no source connects them, and the dates of heliacal events shift with latitude and with precession. This entry records the suggestion and declines to adopt it.

References

  1. Jean Meeus. Astronomical Algorithms. Richmond, Virginia: Willmann-Bell, 1998. ISBN 0943396611 recordscholarly

    Second edition, 1998. The standard reference for the algorithms behind solstice, equinox and solar-longitude computation, including the equinox and solstice chapter this site's seasonal calculations follow.

  2. Bonnie Blackburn, Leofranc Holford-Strevens. The Oxford Companion to the Year: An Exploration of Calendar Customs and Time-Reckoning: Oxford University Press, 1999. ISBN 9780192142313 recordscholarly

    A reference work on calendar customs, calendar reform and time-reckoning, including the Julian and Gregorian rules and the accumulated offset between them.

  3. Ronald Hutton. The Stations of the Sun: A History of the Ritual Year in Britain: Oxford University Press, 1996, xx + 542 pp.. ISBN 0198205708 recordpeer reviewed

    The indispensable single book on the British ritual year and its documented customs.

  4. Kim McCone. Pagan Past and Christian Present in Early Irish Literature. Maynooth Monographs 3. Maynooth: An Sagart, 1990. ISBN 9781870684101 recordpeer reviewed

    Argues that early Irish literature is the product of a monastic culture constructing a native past on biblical and patristic models, rather than a transcript of oral pre-Christian tradition.

  5. A. G. van Hamel (ed.). Compert Con Culainn and Other Stories. Mediaeval and Modern Irish Series III. Dublin: The Stationery Office, 1933 (composed Old Irish, 8th-9th c.). https://archive.org/details/compertconculain03hame recordprimary source

    Contains the edition of Tochmarc Emire, the tale in which the four Gaelic quarter-days are named with a seasonal gloss each. Predates the ISBN system; reprinted by the Dublin Institute for Advanced Studies.