They weren’t sure, with the blanket of cloud, how many people would come by.
But they pulled into the Clontarf car park, and lugged their telescopes from the boots of their cars, and trained them on the pale-yellow moon.
Robin Moore stood on the tarmac in a high-vis jacket, and pointed to Vega, which flickered dimly in the sky.
Years back, he picked up some star names from a novel he read, and rolled them out in front of friends one night, on a trip to Lough Derg in Donegal, away from the city lights.
They asked him more. How far away is that star? How big is it? He decided he would learn.
“Now, there’s another one,” he says, and points a beam at Altair. He traces a shape. “They are part of what’s known as the Summer Triangle … Oh, you can see it!”
Some nights, there are queues to look through the telescopes of these sidewalk astronomers. Some nights are quieter.
It’s an offshoot of the Irish Astronomical Society, which itself dates back to the 1930s, a time when enthusiasts were looking for ways to share what they might have seen or learnt, says Val Dunne, the treasurer.
“In those days, there wasn’t much information available,” he says. They had exhausted the library books and occasional newspaper reports.
“Little groups started to swap information,” he said. There is so much more available now. But there’s nothing like seeing it.
So twice a month, they park up – one evening in Sandymount, the other in Clontarf – and invite passers-by to use their equipment.
As others do across the world, on street corners in Los Angeles, on pavements in Waikiki, on sports pitches in Nicosia – all inspired by a Ramakrishna astronomer monk, who did the same in San Francisco in the 1960s and kicked off a global movement.
There’s no charge, they stress. It’s all for free.
John Dolan flicks through bright images on his phone. That’s how he got interested. He wanted to take photos of the sky.
In the month after he retired, he dug a hole in his back garden. A truck dumped in two tonnes of wet concrete, and onto that went a metal frame.
He bolted down his telescope, so it wouldn’t vibrate with passing north-Dublin traffic. “And I dropped a garden shed around it,” he says.
When there’s a clear night, he might stay up beneath the roll-off roof. Or set an alarm in time to capture a passing asteroid over Glasnevin.
On nights like these, though, he will show his photos of clouds of dust or gas. Or of Jupiter, round like a marble. Or of M31, the Andromeda Galaxy.
He will explain to passers-by that the Milky Way Galaxy is our city of stars. That the stars we see belong to our city. And that Andromeda is another city, in the distance.
As if “we’re in Dublin, we’re looking at Cork”, he says. “But we can’t see the individual street lights in Cork. we just see the glow of the light.”
In his photo, another galaxy, M110, glows further in the background. “Anyway, that just goes to show how insignificant we are,” he says.
Above, the clouds have failed to clear.
“The funny thing is it was clear about an hour ago,” says John Cronin, with a laugh, who learnt of the night from his wife, who learnt of it through a post on a hyper-local website.
He walked over from his home in Clontarf for the first time, this evening.
“I wouldn’t have the gear, but I love that somebody bothers to come down and give me the opportunity to do it,” he says.
He is a scientist by trade, these days computer science; before, it was spectroscopy. “But I’ve never had the money for the toys,” he says.
He looks up: “This moon might come out yet.”
After a while, Cronin crosses the car park to try a second telescope. Perhaps, the clouds might slide aside for a moment.
On the far shore, the Poolbeg peninsula glows with orange and white lights. They could often see more if they set up deep in the Dublin Mountains, or northwards, out of the city.
“But if we do that, we won’t get the average guy who’s walking on the prom, who’ll say, ‘What are you doing guys?’, or he’ll see us on the internet, and come down and have a look,” says Dunne.
It would make the trek too long. Fewer would stumble on them.
“Wow, what is that?” says a young boy, wrapped up against the cold.
One of the sidewalk astronomers points a laser beam of light that seems to reach from his hand, out into the sky, and touch the star. “That is part of Cassiopeia,” he says.
“That’s amazing,” says the boy. “It looks like a W.”
“All I can see is a triangle,” says another, even smaller, boy.
Dunne stands behind his telescope.
If the sky were clearer, he would likely show them the grains of light on the dark side of the moon, where the sun’s rays catch the tips of mountains.
He loves Saturn and the deep-sky objects. But the moon is special. “It’s my favourite of all the objects,” he says. “Because it’s changing all the time.”
At one end of the car park, a group of people tip their heads back and track a new speck of light that has appeared.
“We thought it was an aeroplane,” says one, as the International Space Station arcs across the sky.
“She’ll go now,” says Dunne. “One. Two. Three. She’s nearly gone now … there she is.”
They talk over each other – What was it? What height is that? Are they waving, do you think? – as it disappears, as if a page has turned.
“Where’s it gone?” asks a man.
“She’s just gone into the Earth’s shadow,” says Dunne.
“Into the Earth’s shadow,” says a woman.
CORRECTION: This article was updated at 9.04am on 23 October 2023, to correct that Andromeda is catalogued as M31, not M21. Sorry for the error.