Spectators have gathered at the Neolithic burial mound at Newgrange, Co Meath, for the winter solstice.
However, heavy cloud cover meant that the passageway and chamber of the 5,000-year-old tomb were not illuminated by the rising sun.
Access to the chamber this morning was decided by lottery.
Thousands of people also descended on ancient holy sites in southern Mexico to celebrate a new cycle in the Mayan calendar.
Brightly dressed indigenous Mexican dancers whooped and invoked a serpent god near the ruins of Chichen Itza last night, while meditating westerners hoped for the start of a "golden age" of humanity.
People were celebrating the close of the 13th bak'tun - a period of some 400 years - in the 5,125-year-old Long Calendar of the Maya.
There were fears in some quarters that the new cycle might instead herald the end of the world, which was meant to have happened at 11.11am.
A US scholar had once said the end of the cycle could be seen as a kind of "Armageddon" by the illustrious Mesoamerican culture, and over time the idea snowballed into a belief that the Mayan calendar had predicted the earth's destruction.
Maya experts, scientists and even US space agency NASA insist the Maya did not predict the world's end and that there is nothing to worry about.
"Think of it like Y2K," said James Fitzsimmons, a Maya expert at Middlebury College in Vermont. "It's the end of one cycle and the beginning of another cycle."
