Also spelled Lughnasad and later called Lammas, this holiday is traditionally celebrated on August 1st but as a cross-quarter day (halfway between the solstice and equinox) is more properly when the Sun is at 15 degrees Leo which is the midpoint between the Summer Solstice and the Autumnal Equinox, although it is also sometimes celebrated on the full moon nearest the midpoint.
For modern pagans, the cross-quarter days are the most magical times of the year, when the veil between the worlds (the spiritual and physical planes) becomes thinner and more easily traveled.
Lughnasadh is an ancient Celtic festival honoring the god Lugh for his triumph over the spirits of the other world who tried to keep the harvest for themselves. It was a celebration of the abundance of the Earth, and also a time of sports and games to celebrate good health and physical vitality, all aspects of Leo. Some sources say that Lughnasadh was a time for the crowning of kings, another correspondence of Leo. In some traditions this is a time when the corn god is sacrificed in order to guarantee the harvest, and the eating of bread is a major part of rituals and celebrations of the festival.
The Lughnasadh festival was later reborn in Medieval Christianity as Lammas (loaf-mass), in which a loaf of bread made from the newly harvested wheat was brought to church. St. Catherine’s Day was often celebrated at Lammas with the Catherine Wheel which was set aflame and rolled down a hill, reminiscent of the pagan fire festivals of the cross quarter days.
This year the accurate cross-quarter date falls on August 6, with the closest Full Moon on August 8th.