Twenty people will this morning huddle together in a man-made underground cave, modern participants in a ritual first performed by our Neolithic ancestors 5,000 years ago.
As of old, the Newgrange observations are a week-long event, with sunlight reaching the rear wall of the grave three days before and after yesterday's December 21st solstice. So observers will watch the magic unfold this morning, tomorrow and Wednesday - weather permitting - before the chance in 1997 is lost and would-be solar observers have to wait another 12 months.
The ritual, its hidden mystery and the cave, actually a passage grave, are linked to Newgrange, part of the Bru Na Boinne monument north of Drogheda, Co Louth. Built in 3200 BC and concealed for centuries until it was rediscovered almost 300 years ago, Newgrange represented a particularly fine example of this sort of monument, but little more than that until 1963.
In that year archaeological excavations revealed a small box-shaped opening above the passage entrance, no more than 25cm high. Scientists pondered the roof box's significance until its importance was confirmed 30 years ago yesterday, when the professor of archaeology at UCC, Mr M.J. O'Kelly, watched a shaft of dawn sunlight penetrate the 24-metre passage to strike the rear wall of the grave.
It showed without a doubt that the grave was aligned to observe the winter solstice, the shortest day of the year, explained Ms Clare Tuffy, manager of visitor services at Newgrange. "It is the oldest known deliberately solar-oriented structure anywhere in the world," she said.
It is a contemporary of the Step pyramids at Saqqara, but predates the Giza pyramid by about 500 years and the famous Stonehenge by 1,000 years. Its date of construction was set by the radiocarbon dating of burnt clay and sand mixed as a caulk to seal between the passage stones and keep it watertight, Ms Tuffy said.
"When Prof O'Kelly found the roof box opening he didn't know what it was for." The view that the Stone Age Irish had the astronomical and engineering skills to build a solar observatory was considered "outrageous" by scientists, she added.
He went into the passage alone before dawn on December 21st, 1967, to see if sunlight could clear the roof box and reach all the way into the grave. He was not disappointed and became the first modern Irishman to see this since the passage was hidden. "It implies that we had skilled astronomers and engineers, not just part-timers, but full-time professional monument builders," Ms Tuffy believes.
Much scientific analysis of Newgrange has occurred since then. Prof Tom Ray, of the Dublin Institute of Advanced Studies, calculated how the Earth's orbital "wobble" had altered the timing of the solstice event at Newgrange, reducing viewing time by four minutes compared with 5,000 years ago.
The beam is also "shorter", first striking the floor a metre in front of the back wall before tracking to it. In 3200 BC observers would have seen the first shaft of dawn light reach directly to this wall.
Not experiencing a bright sunny December morning is no impediment to experiencing the drama of the solstice at Newgrange, Ms Tuffy believes. "I am sure that the people who built the monument were disappointed the odd time or two."
