The Summer Solstice is observed on June 21 to celebrate the longest day of the year all across the globe. In ancient times, the Celtics did not have clocks or calendars, so they measured the time often by the way the sunlight hit various passages in stone monuments set up for this exact purpose. The festival or celebration was called Alban Heruin. Traditionally, this was the time when the sun was at its highest point in the sky and shed three rays of light onto the world.
The celebration is also commonly known as Midsummer’s Eve or Day. It is also called Tairisem in Ireland which means that the sun has stood still. Celebrations included feasts, picnics, bonfires and games all to honor the White Mare Goddess Éatain Eachraidhe who is also known as Rhiannon in Wales.
Sunlight would pass as the Midsummer Day approached into various passages in stone arrangements like that of Newgrange. It would light up a section of the stone precisely to indicate that the longest day of the year was approaching or had arrived. This usually was the 20th or 22nd of what we now call the month of June.
The sun still hits the various stone arrangements the same way as it did in ancient Druid times, which still indicates the arrival of the longest day of the year. In South Dublin, Ireland, the longest day makes itself known by the sun’s exact alignment over Lambay Volcano and a less famous monument than Stonehenge positioned on Tallaght Hill.