A full Moon rises as the last rays of sunlight illuminate the Roches Point Lighthouse in Cork Harbour, Ireland. David Creedon David Creedon

JUST ONCE IN a very blue moon, there’s a chance to witness a pretty rare lunar event. 

Yes, a so-called blue moon will be visible over Ireland overnight. 

But as we probably gave away with the ‘so-called’, it’s a pretty safe bet to predict said moon will not in fact be blue.

A blue moon is the name given to the second full moon in the same calendar month.

We had the first one on 1 May, so the full moon tonight, 30 May, becomes a ‘blue moon’.

Blue moons occur only every two to three years.

Astronomy Ireland is encouraging people to take pictures of the phenomenon.

“Full moons at this time of year are very low in the sky, which is perfect for photos lining up the moon over landmarks, people and events,” the magazine’s editor David Moore said.

People can send their photos of the moon into Astronomy Ireland.

The earliest moonrise from Ireland tonight is 9.30pm and on Sunday it is at 10.35pm. 

Weather conditions for viewing it are not the worst – there’s a mix of scattered showers and clearer spells forecast.