Lughnasadh is the festival of the beginning of harvest. The name means “funeral games of Lugh” – Lugh being (perhaps) the ancient Irish Sun God, and God of the Corn. Lugh, however, is not the one whose funeral it is, but Tailtiu, his (foster-)mother, who is identified with the Earth itself.

There are numerous ideas concerning exactly when this festival is to be observed. Many sources give July 31st/ August 1st, and a few point to August 6th. However, the cross-quarter day itself is the halfway point between the summer solstice (Midsummer) and the autumnal equinox (Mabon) and since that definition is independent of human calendar systems (works for both hemispheres). So, today’s the day, up here in the top half of the planet.
There’s an overview of controversies surrounding the origin of the festive by Kym ní Dhoireann which casts doubt on Lugh’s being a solar deity at all…
There is a great deal of showing off associated with Lughnasadh: athletic feats, musical and poetic recitals, storytelling, displays of crafts and skills of many kinds. And hand-fastings. It is a propitious time for the conception of babies, who will be born after the end of winter, around Beltane.
The most thorough overview of the neopagan writings on Lughnasadh that I’ve come cross is this one by Kathleen Jenks. The Wikipedia entry is nothing to write home about.
Here are some recipes for the occasion. Bread is a big feature of the day (Lugh being a Corn God, and all); accordingly, there will be home made pizza tonight…
(graphic by Aquila Kegan)