Met Eireann says there is only a "slight chance" that the sun will be visible for the winter solstice at the Neolithic burial mound in Newgrange this morning.
Enthusiasts will be hoping for an unexpected break in the cloud like the one which enabled hundreds of thousands of people around the State to view the solar eclipse this summer.
However, a spokesman for Met Eireann said that while they expect that rain will have cleared from Newgrange by first light, an "overhang of cloud" is likely to obscure the sun.
Every year for five days around the time of the winter solstice the opening above the doorway to the passage grave catches the rays of the rising sun. The inner burial chamber will first be illuminated by the dawn light at 8.58 a.m.
While the sun illuminates most of the 19-metre underground tunnel, it does not quite reach the chamber at the back. This is not the result of a design fault, but is due to the fact that the angle at which the Earth is tilted at this time of year has changed by half a degree over the 5,000 years since the mound was built.
RTE will transmit the event live from inside the chamber between 8.58 a.m. and 9.15 a.m. in the course of an hour-long programme beginning at 8.30 a.m. It will also be broadcast on the station's website at www.rte.ie.
Newgrange traditionally celebrates the solstice on December 21st even though it sometimes occurs on December 22nd, as is the case this year. The actual moment of solstice tomorrow is 7.44 a.m.
