A partial eclipse of the sun takes place on Christmas Day.
An eclipse on December 25th is a rare event. The last was in 1954. There was one in 1973 on Christmas Eve, and the next is not due before 2038.
The closest point to Ireland where the event may be witnessed will be about 1,000 km west of Achill.
Those lucky enough to be travelling to North America on December 25th will get an extra present.
The best place for highly populated areas to see the eclipse will be on the northeast side of the United States, according to Mr David Moore, chairman of Astronomy Ireland.
"Some people will see as highly significant the fact that the last sun eclipse of the old millennium is taking place on Christ's birthday - and that it will be visible to most people from the most powerful country on the planet," he said.
No doubt some astrologers will be predicting the end of the world, Mr Moore added. Maximum eclipse - when 72 per cent of the sun will be covered by the moon - may be seen from northern and eastern Canada and the north-east of the USA.
But even Californians and Mexicans will see the moon "bite" a small chunk out of the sun.
A total eclipse of the moon will be visible from Ireland on January 9th, however, said the Astronomy Ireland chairman.
The best time to see it will be 8.20 p.m. Astronomy enthusiasts are asked to share the experience in the Phoenix Park, where powerful telescopes will be in use to make the most of the occasion.