The Gaelic calendar, or alternatively the Irish calendar, is a system of timekeeping developed during Ireland's Gaelic era and is still in popular use in modern Ireland. It is used to define the beginning and length of the day, the week, the month, the seasons, quarter days, and festivals. The Gaelic calendar does not observe the astronomical seasons that begin in the Northern Hemisphere on the equinoxes and solstices, or the meteorological seasons that begin on March 1, June 1, September 1, and December 1. Rather, the middle of the seasons in the Gaelic calendar fall around the solstices and equinoxes. As a result, for example, Midsummer falls on the Summer Solstice. Like elsewhere, the modern Irish calendar begins on 1 January, the ancient Celtic year begins on 1 November.
The seasons in Ireland today still follow this ancient Celtic tradition, which is based solely on daylight and the strength of the noon sun. As such, the seasons of the year are observed in Ireland as follows:
- Winter ("Geimhreadh") - November, December, January (Samhain, Nollaig, Eanáir)
- Spring ("Earrach") - February, March, April (Feabhra, Márta, Aibreán)
- Summer ("Samhradh") - May, June, July (Bealtaine, Meitheamh, Iúil)
- Autumn ("Fómhar" Harvest) - August, September, October (Lunasa, Meán Fómhair, Deireadh Fómhair)
This is a continuation of the Celtic and Gaelic system, which is pagan in origin. This is particularly evident in the Irish (Gaeilge) names for May (Bealtaine), August (Lúnasa) and November (Samhain), which were the names of Gaelic pagan festivals. In addition, the names for September (Meán Fómhair) and October (Deireadh Fómhair) translate directly as "middle of harvest" and "end of harvest". Christianity has also left its mark on the Irish months: the name for December (Nollaig) derives from Latin natalicia (birthday), referring to the birth of Christ.
Historical texts suggest that, during Ireland's Gaelic era, the day began and ended at sunset. Through contact with the Romans, the seven-day week was borrowed by continental Celts, and then spread to the people of Ireland. In Irish, four days of the week have names derived from Latin, while the other three relate to the fasting done by Catholic clergy. Dé Luain; Dé Máirt; Dé Sathairn; Dé Domhnaigh.
- Dé Luain - from Latin dies Lunae
- Dé Máirt - from Latin dies Martis
- Dé Chéadaoin - referring to Catholic fasting: from céad (first) aoin (fast) i.e. the first fast of the week
- Déardaoin - the day between the fasts
- Dé hAoine - the day of the fast
- Dé Sathairn - from Latin dies Saturni
- Dé Domhnaigh - from Latin dies Dominicus (an alternative Latin name for Sunday, dies Solis being more common)
- See Nora Chadwick, The Celts (1970) p.181
- Koch, John T. Celtic Culture: A Historical Encyclopedia. ABC-CLIO (2006). Page 330.
- Koch, John T. Celtic Culture: A Historical Encyclopedia. ABC-CLIO (2006). Page 331.