I should have posted this about a week ago as the time was germane to the topic but here goes now anyway.
The Iron Age Celts counted time in terms of nights rather than days and the passing of moons rather than months while the celebration of Féis, or festivals, at regular intervals marked the passing of the years.
The most commonly observed féis included:
Bealtaine (May 1) which was observed by lighting bonfires, the smoke of which had purifying powers and was used to kill pests on cattle. I think it might also have been an early harvest time but i couldn’t swear to it.
Next up was Lugnasa aka Lughnasadh and Lughnasa. (Aug. 1) which was the festival marking the beginning of the harvest season. Originally it was held on or about halfway between the summer solstice and autumn equinox. The festival itself is named after the god Lugh. It involved great gatherings that included druidic ceremonies, ritual athletic contests (most notably the Tailteann Games, Áenach Tailten which were held at Tailtin in County Meath), feasting, matchmaking and trading while community rites included an offering of the first of the grain crops, a feast of the new food and of bilberries, the sacrifice of a bull and a ritual dance-play. Much of this would have taken place on top of hills and mountains.
Samhain (Nov. 1) was the start of the Celtic year and was, again, a time for sacrifices and community gatherings. Rememberance of spirits of the dead was a prominent feature while the festival also marked the end of the harvest season and the beginning of winter or the “darker half” of the year, the time when cattle were brought back down from the summer pastures and when livestock were slaughtered for the winter. As at Bealtaine, special bonfires were lit. These were deemed to have protective and cleansing powers.
Finally, Imbolc (Feb. 1) marked the beginning of spring and fertility, renewal and purification and the yearly cycle continued its round.
Interestingly, in the fifth Century when St. Patrick brought Christianity to Ireland, rather than trying to stamp out these “pagan” festivals, the early church commandeered them – Samhain becoming All Souls Day and Easter taking over Bealtaine. St. Paddy himself used the sun symbol of the god Lugh superimposed on the Christian cross to make what is widely known now as the “celtic cross”.