Beltane or Bealtaine is an ancient Gaelic holiday celebrated around May 1. Historically, this festival was celebrated in Ireland, Scotland and the Isle of Man. There were similar festivals held at the same time in the other Celtic countries of Wales, Brittany and Cornwall. The festival survives in folkloric practices in the Celtic Nations and the diaspora, and has experienced a degree of revival in recent decades. For the Celts, Beltane marked the beginning of the pastoral summer season when the herds of livestock were driven out to the summer pastures and mountain grazing lands. In modern Irish, Mí na Bealtaine ('month of Bealtaine') is the name for the month of May. The name of the month is often abbreviated to Bealtaine, with the festival day itself being known as Lá Bealtaine. The lighting of bonfires on Oidhche Bhealtaine ('the eve of Bealtaine') on mountains and hills of ritual and political significance was one of the main activities of the festival.In modern Scottish Gaelic, Là Buidhe Bealltaine ('the yellow day of Bealltain') is used to describe only the first of May.
In ancient Ireland the main Bealtaine fire was held on the central hill of Uisneach 'the navel of Ireland', the ritual centre of the country, which is located in what is now County Westmeath. In Ireland the lighting of bonfires on Oidhche Bhealtaine seems only to have survived to the present day in County Limerick, especially in Limerick itself, as their yearly bonfire night, though some cultural groups have expressed an interest in reviving the custom at Uisneach and perhaps at the Hill of Tara. The lighting of a community Bealtaine fire from which individual hearth fires are then relit is also observed in modern times in some parts of the Celtic diaspora and by some Neopagan groups, though in the majority of these cases this practice is a cultural revival rather than an unbroken survival of the ancient tradition.
Another common aspect of the festival which survived up until the early 20th century in Ireland was the hanging of May Boughs on the doors and windows of houses and of the erection of May Bushes in farmyards, which usually consisted either of a branch of rowan (mountain ash) or whitethorn (hawthorn) which is in bloom at the time and is commonly called the 'May Bush' in Hiberno-English. The practice of decorating the May Bush with flowers, ribbons, garlands and colored egg shells has survived to some extent among the diaspora as well, most notably in Newfoundland, and in some Easter traditions observed on the East Coast of the United States.
Beltane is a cross-quarter day, marking the midpoint in the Sun's progress between the vernal equinox and summer solstice. Since the Celtic year was based on both lunar and solar cycles, it is possible that the holiday was celebrated on the full moon nearest the midpoint between the vernal equinox and the summer solstice. The astronomical date for this midpoint is closer to May 5 or May 7, but this can vary from year to year. (Wikipedia)