Lughnasa was not actually that big a part of the play and subsequent film Dancing at Lughnasa.
The story was so captivating, it’s easy to focus on that and forget all about the name. But Lughnasa was once a fairly important event in Ireland. It was the Celtic harvest festival, and it was named for the ancient God Lugh.

Lughnasa falls on the first of August. This is rather early for a harvest festival, but it is known as the first fruits harvest, not the final autumn harvest. Two things explain the date – aside from it being the time to start harvesting some crops. The movement of the sun was vitally important to early Irish peoples, as monuments such as Newgrange and Loughcrew show. The solar year has four major highlights: winter solstice, spring equinox, summer solstice and autumn equinox. The ancient Celts also celebrate four days halfway between those events known as cross quarter festivals. Over time, Imbloc, Beltane, Lughnasa and Samhain grew bigger in Ireland than the main solar events.
The second explanation for the date of Lughnasa comes from Celtic mythology. The story goes that Lugh declared August first a holiday to commemorate his foster mother’s death. Tailu, his foster mother, collapsed and died after exhausting herself clearing fields to plant crops. (Possibly, this explains a thing or two about Irish mothers and martyrdom.) The grief-striven god of the Tuatha De Danann declared a festival to be held on the date of her death for feasting and games in her honor.
Who Was Lugh?
Lugh was one of the most important of the Tuatha De Danann’s gods. While he is often described as the fire god or the sun god, He was a grandson of Balar, and an ancestor of the legendary warrior Cú Cuchlainn. Like many ancient gods and goddess, this tribe took family dysfunction to epic levels. Balar’s tribe was at war with the Tuatha De Danann, and in one version, he sought to make peace by marrying his daughter Eithne to their leaders, Cian. In another version, Cian seduces Eithne when he goes to retrieve a cow Balar has stolen from him.
In both versions, Eithne gives birth to triplet boys and Balar throws her and the babies into the sea. Cian is only able to rescue one – Lugh. The triplets show the importance of the number three to the early Celts. They also worshipped a triple goddess and carves triple spirals into Newgrange and other important locations.
Eithne’s death left Lugh to be raised by Tailu. He grew up to be a great warrior and led the Tuatha De Danann into their ultimate battle against Balar’s tribe, the Fomoire. Lugh killed Balar in the conflict at the field of Mag Tuired, and that was the end of the Fomoire. While the battlefield Mag Tuired is mythical, some scholars believe that County Louth takes its name from the warrior god Lugh.

Over the centuries, Lughnasa grew into a fair day. The Puck Fair in County Kerry is held in early August and is believed to have derived from Lughnasa. Reek Sunday, the last Sunday in July when Christians climb Croagh Patrick as a pilgrimage, is likely to have begun to distract early Christians from the ancient pagan celebrations.