The Celtic calendar is a compilation of pre-Christian Celtic systems of timekeeping, including the Gaulish Coligny calendar, used by Celtic countries to define the beginning and length of the day, the week, the month, the seasons, quarter days, and festivals.
Continental Celtic calendar
The Gaulish Coligny calendar is the oldest known Celtic solar-lunar ritual calendar. It was discovered in Coligny, France, and is now on display in the Palais des Arts Gallo-Roman museum, Lyon. It dates from the end of the second century CE, when the Roman Empire imposed the use of the Julian Calendar in Roman Gaul. The calendar was originally a single huge plate, but it survives only in fragments. It is inscribed in Gaulish with Latin characters and uses Roman numerals.
The Coligny Calendar is an attempt to reconcile the cycles of the moon and sun, as is the modern Gregorian calendar. However, the Coligny calendar considers the phases of the moon to be important, and each month always begins with the same moon phase. The calendar uses a mathematical arrangement to keep a normal 12 month calendar in sync with the moon and keeps the whole system in sync by adding an intercalary month every 2 1⁄2 years. The Coligny calendar registers a five-year cycle of 62 lunar months, divided into a "bright" and a "dark" fortnight (or half a moon cycle) each. The months were possibly taken to begin on the new moon, and a 13th intercalary month was added every two and a half years to align the lunations with the solar year.
The astronomical format of the calendar year that the Coligny calendar represents may well be far older, as calendars are usually even more conservative than rites and cults. The date of its inception is unknown, but correspondences of Insular Celtic and Continental Celtic calendars suggest that some early form may date to Proto-Celtic times, roughly 800 BCE. The Coligny calendar achieves a complex synchronisation of the solar and lunar months. Whether it does this for philosophical or practical reasons, it points to a considerable degree of sophistication.
Medieval Irish and Welsh calendars
Among the Insular Celts, the year was divided into a light half and a dark half. As the day was seen as beginning at sunset, so the year was seen as beginning with the arrival of the darkness, at Calan Gaeaf / Samhain (around 1 November in the modern calendar). The light half of the year started at Calan Haf/Bealtaine (around 1 May, modern calendar). This observance of festivals beginning the evening before the festival day is still seen in the celebrations and folkloric practices among the Gaels, such as the traditions of Oíche Shamhna (Samhain Eve) among the Irish and Oidhche Shamhna among the Scots.
Julius Caesar said in his Gallic Wars: "[the Gaulish Celts] keep birthdays and the beginnings of months and years in such an order that the day follows the night." Longer periods were reckoned in nights, as in the surviving English term fortnight meaning two weeks, and the obsolete se'nnight meaning one week.
The Laws of Hywel Dda (in editions surviving from the 12th and 13th centuries) make repeated references to periods of nine days (nawfed dydd), rather than the "eight nights" that make up the current word wythnos.
Native calendar terms in Celtic languages
Many calendrical and time-keeping terms used in the medieval and modern Celtic languages were borrowed from Latin and reflect the influence of Roman culture and Christianity on the Insular Celts. The words borrowed include the month names Januarius (Old Irish Enáir, Irish Eanáir, Welsh Ionawr), Februarius (Old Irish Febra, Irish Feabhra, Welsh Chwefror), Martius (Old Irish Mart, Welsh Mawrth), Aprilius (Old Irish Apréil, Irish Aibreán, Welsh Ebrill), Maius (Welsh Mai), Augustus (Old Irish Auguist, Welsh Awst); the names for the days of the week, Solis, Lunae, Martis, Mercurii, Jovis, Veneris, Saturni; the terms septimana "week" (Old Irish sechtmain, Breton sizun, Cornish seithun), kalendae "first day of the month" (Old Irish callann, Welsh calan, Breton kala), tempore "time" (Welsh amser), matutina "morning" (Cornish metin, Irish maidin), vespera "evening", nona "noon" (Welsh nawn, Irish nóin), and ôra "hour" (Welsh awr, Breton eur, Irish uair).
A number of native Celtic terms survived the adoption of the Roman/Christian calendar, however:
|Term||Proto-Celtic||Gaulish||Old/Middle Irish||Modern Irish||Scottish Gaelic||Manx||Welsh||Cornish||Breton|
|Day / 24-hour period||*latįon||lat (abbreviation, Coligny Calendar)||la(i)the||lá||là, latha||laa||golau go + lau = very bright; golau = light|
|Day||*diį-||(sin)diu "(to)day"||día; indiu "today"||dia, dé; inniu, inniubh, inniugh "today"||dia; andiu "today"||jee; joo "today"||dydd; heddiw "today"; diwrnod "24-hour day period"||dydh; hidhyw "today"||deiz; hiziou "today"|
|Night||*nokWt-, *ad-akWi-(?)||(tri)nox "(3)-night", (decam)noct- "(10)-night"||nocht, adaig||nocht, oíche||nochd, oidhche||noght, oie||noson, nos||neth (comp.), nos||neiz (comp.), noz|
|Week (eight nights/days)||*oktu-nokWt- / *oktu-diį-||wythnos "8-nights"||eizhteiz "8-days"|
|Fortnight||*kWenkWe-decam-nokWt-||cóicthiges "15-(days)"||coicís||cola-deug (coig latha deug "15-days")||kegeesh||pythefnos "15-nights"||pemzektez|
|Month||*mīss-||mid (read *miđ)||mí||mí||mìos||mee||mis||mis||miz|
|Year||*bl(e)id-anī-||b[l]is (abbreviation, Coligny Calendar)||bliadain||bliain||bliadhna||blein||blwydd, blwyddyn||bledhen||bloavezh, bloaz|
|Season, Period of Time||*ammn, *ammn-stero-, *ratio-, *pritu-||amman||amm, aimser, ráithe||aimsir||àm, aimsir, ràith||imbagh, emsher||amser, pryd||amser||amzer|
|Spring||*ers-āko "end (of winter)" (alt. *uesr-āko "spring[time]"), *ues-ant-ēn-, *ro-bertiā ("torrent, inundation")||earrach, robarta||earrach||earrach||arragh||gwanwyn, (Old Welsh ribirthi)||gwainten||reverzi (Old Breton rebirthi)|
|Autumn||*uφo-gijam-r- "under wintertime", *kintu-gijamo "beginning of winter", *sito-[...] "deer-"[...]||fogamur||fóghmhar, fómhar||foghar||fouyr||cynhaeaf, hydref||kydnyav/kynyav, hedra||here, diskar-amzer ("falling season")|
|May, May Day||*kintu-sam?n- "beginning of summer"||Cétamain||Cèitean||Céideamhain||Cyntefin|
|June, Midsummer||*medio-sam?n- "mid-summer"||Mithem(on)||Meitheamh||Mehefin||Metheven||Mezeven|
|July||*uφer-kwenno-samo- "end of summer"||Gorffennaf|
In some Neopagan religions, a "Celtic calendar" loosely based on that of Medieval Ireland is observed for purposes of ritual. Adherents of Reconstructionist traditions may celebrate the four Gaelic festivals of Samhain, Imbolc, Beltane and Lughnasadh.
Some eclectic Neopagans, such as Wiccans, combine the Gaelic fire festivals with solstices and equinox celebrations derived from non-Celtic cultures to produce the Wiccan modern Wheel of the Year.:337 Some eclectic Neopagans are also influenced by Robert Graves' "Celtic Tree Calendar", which has no foundation in historical calendars or actual ancient Celtic Astrology, instead being derived from Graves' vision of The Song of Amergin.:145
- Koch, John T. (2006). Celtic Culture: A Historical Encyclopedia. ABC-CLIO. p. 330.
- Duval, P.M.; Pinault, G., eds. (1986). "Les Calendriers (Coligny, Villards d'Heria)". Recueil des inscriptions gauloises. 3. Paris: CNRS. p. 35.
- Eddy, S.; Hamilton, C. "The Celtic Year". Living Myths. Retrieved 29 June 2020.
- Lyle, Emily B. (1994). "The starting-points in the Coligny Calendar". Études celtiques. 30: 285–289.
- Danaher, Kevin (1972). The Year in Ireland: Irish Calendar Customs. Dublin: Mercier. pp. 200–229. ISBN 1-85635-093-2.
- McNeill, F. Marian (1961). The Silver Bough. 3. Glasgow: William MacLellan. pp. 11–42.
- Wade-Evans, Arthur (1909). Welsh Medieval Laws. Oxford University Press. Retrieved 31 January 2013.
- Loth, Joseph (1892). Les mots latins dans les langues brittoniques. E. Bouillon. p. 44 ff.
- "Online edition". Dictionary of the Irish language. Royal Irish Academy. 1983.
- Jackson, Kenneth Hurlstone (1967). A historical phonology of Breton. Dublin Institute for Advanced Studies. pp. 296, 248.
- Hamp, Eric (1982). "The Indo-European roots *bher- in the light of Celtic and Albanian". Zeitschrift für celtische Philologie. 39: 205–218.
- In the reconstructed Proto-Celtic words for the beginning of summer, "kintu-sam?n", and mid-summer, "medio-sam?n", the character "?" represents an indeterminate vowel.
- "mayday". www.teanglann.ie.
- Bonewits, Isaac (2006). Bonewits's Essential Guide to Druidism. New York, NY: Kensington Publishing Group. p. 134. ISBN 0-8065-2710-2.
- McColman, Carl (2003). Complete Idiot's Guide to Celtic Wisdom. Alpha Press. pp. 12, 51. ISBN 0-02-864417-4.
- Hutton, Ronald (1991). The Pagan Religions of the Ancient British Isles: Their nature and legacy. Oxford, UK: Blackwell. ISBN 0-631-18946-7.
- Brennan, Martin (1994). The Stones of Time: Calendars, Sundials, and Stone Chambers of Ancient Ireland. Rochester, VT: Inner Traditions.
- Brunaux, Jean-Louis (1986). Les Gaulois: Sanctuaires et Rites [The Gauls: Sanctuaries and ceremonies]. Paris: Editions Errance.
- Duval, Paul-Marie; Pinault, Georges (eds.). "The calendars of Coligny (73 fragments) and Villards d'Heria (8 fragments)". Recueil des Inscriptions Gauloises (R.I.G.). 3.
- Delamarre, Xavier (2003). Dictionnaire de la langue gauloise [Dictionary of the Gaulish Language]. Paris: Editions Errance.
- "online edition". Dictionary of the Irish language. Dublin: Royal Irish Academy. 1983.
- "online edition". Geiriadur Prifysgol Cymru (2nd ed.). Cardiff: University of Wales Press. 2002.
- Jackson, Kenneth Hurlstone (1953). Language and History in early Britain. Edinburgh: Edinburgh University Press.
- Jackson, Kenneth Hurlstone (1967). A Historical Phonology of Breton. Dublin: Dublin Institute for Advanced Studies.
- Jenner, Henry (1982). A Handbook of the Cornish Language. New York: AMS Press. pp. 203 ff. ISBN 0404175570. (reprint of 1904 ed.)
- Koch, John, ed. (2006). "Calendar, Celtic". Celtic Culture: a historical encyclopaedia. Santa Barbara: ABC-Clio. pp. 330–332.
- Lambert, Pierre-Yves (1995). La langue gauloise [The Gaulish Language]. Paris: Editions Errance. pp. 109–115.
- Loth, Joseph (1892). Les mots latins dans les langues brittoniques. Paris: E. Bouillon.
- Matasović, Ranko (2009). Etymological Dictionary of Proto-Celtic. Brill Academic Publishers.
- Nance, Robert Morton, ed. (1955). A Cornish-English Dictionary. Marazion: Worden, for the Federation of Old Cornwall Societies.
- Pokorny, Julius (1959–1969). Indogermanisches etymologisches Wörterbuch [[proto-]Indo-Germanic Etymological Dictionary]. Bern-München.
- Schrijver, Peter (1995). Studies in British Celtic Historical Phonology. Amsterdam: Rodopi.
- Vendryes, Joseph; Bachallery, Édouard; Lambert, Pierre-Yves (1959–1996). Lexique étymologique de l'irlandais ancien [Etymological Dictionary of the Ancient Language of Ireland]. Dublin: Dublin Institute for Advanced Studies.