Today is the shortest day of the year and one of the most popular days to view the Winter Solstice at Newgrange.
Every year at the Newgrange passage tomb, a ray of sunlight illuminates the chamber.
A group of people, chosen by a lottery system, gathered in the hope of seeing the phenomenon.
Our @ancienteastIRL colleagues welcomed the #WinterSolstice this morning at #Newgrange where for 5,000 years, a single ray of dawn sunlight has pierced the ancient tomb on the shortest days of the year, marking the end of winter and the start of new life. #Ireland pic.twitter.com/22dzuuGCYM— Fáilte Ireland (@Failte_Ireland) December 21, 2018
It comes as aerial surveys carried out in the summer there have revealed more history about the site.
A group of people, chosen by a lottery system, will gather later in the hope the morning sunrise at 8.56am will illuminate the chamber for 17 minutes.
The Office of Public Works opens the monument for the dawn from December 18 until December 23.
The weather prospects though for the 5,000-year-old site are not good with rain and cloud possible.
Sixty people, including visitors from as far afield as Australia, Brazil and Canada, will have had access to the chamber over those days.
Minister for Culture, Heritage and the Gaeltacht Josepha Madigan, said: "As we celebrate this week, the phenomenon of the winter solstice sunrise illuminating the burial chamber of the passage tomb at Newgrange, this stunning new archaeological information provides fresh, spectacular and unique insights into the origins and development of the Neolithic landscape and society."
However, results of aerial surveys carried out during the summer at the site have been revealed by the National Monuments Service.
They have identified "immense timber enclosures and large ceremonial henges" which they say were once features of the Neolithic landscape close to the tomb in County Meath.
The aerial reconnaissance was carried out at the Brú na Bóinne World Heritage Site following the initial discovery of cropmarks in the parched fields of the River Boyne floodplain in July.
In an interim report published today, the NMS says these were once monuments that "clearly formed a deliberately structured and ritual landscape of great significance".
Minister Madigan, said: "This new information is a graphic illustration of the extent and density of ritual and ceremonial sites associated with the Newgrange Passage Tomb."
Meanwhile, the Department of Culture, Heritage and the Gaeltacht said today's report "will provide a basis for a solid and refreshed research framework to be implemented in coming years in line with the aims of the Brú na Bóinne UNESCO Management Plan".