A spectacular double-act starring Jupiter and Venus will light up the sky tonight.
The two brightest planets will appear to be unusually close together - roughly two-thirds of a full moon's width apart.
They are not about to collide - it is only an illusion caused by line-of-sight. In fact, hundreds of millions of kilometres of space separate the planets.
After tomorrow they will start to go their separate ways again, with Venus below Jupiter.
Don't forget we will have large telescopes set up to view the conjunction. Come and join us for a rare experience. http://t.co/lvUeRGiB9Q— Astronomy Ireland (@AstronomyIRL) June 29, 2015
"The spectacle of the two brightest planets so close together is beautiful and unusual. Many people will wonder what they are seeing, but it's just a natural coincidence," said Robin Scagell, vice-president of the Society for Popular Astronomy.
"Jupiter will appear almost directly above Venus, but the pair will also make a striking sight for an evening or two either side.
"It's a beautiful sight, and one everyone can enjoy. It's unusual for two such bright planets to be so close together, particularly in the midsummer evening sky.
"The time to look is about 10.30 to 11pm. The farther north, the later the time because it gets dark later."
Venus is now just over 90 million kilometres from Earth and Jupiter almost 900 million.
A small telescope or even a pair of binoculars will show the two planets in the same field of view.
At relatively low magnification, Jupiter can be seen as a small circular disc accompanied by four bright moons. Venus will be a fat crescent.
Astronomy Ireland is holding a free event this evening to celebrate the historical merger of Venus and Jupiter.
The event will take place at 9pm, complete with free tea, coffee and refreshments, at their headquarters in Blanchardstown.
The event will be open to the general public and telescopes will be available for star-gazers.
Astronomy Ireland say enthusiasts should be able to see both the discs of Venus and Jupiter in the same field of view, an extremely rare sight that won't be bettered for another 107 years.