It’s a Philly tradition, at least for a certain set of photography-minded individuals — that twice-yearly moment when the sunset aligns perfectly with the city’s grid, offering the opportunity for stunning photos of a sun setting west down Market Street.

A phenomenon known as Phillyhenge.

A nod to the famed Stonehenge in Wiltshire, England, it has become a kind of rite of passage for city photographers of all levels of experience. It’s known to draw dozens to Dilworth Park near City Hall in search of the perfect photo.

The only catch?

The perfect photo requires a good deal of support from Mother Nature.

“You have two to three days where the alignment is correct,” said Tony Collins, a Delaware County-based photographer who does much of his work in Philadelphia. “But is the weather going to cooperate with you?”

It was a question on the minds of area photographers on Saturday, as the weekend’s forecast inspired limited confidence.

Sunny skies on Saturday morning had given way to an overcast evening — and Sunday’s forecast wasn’t any better, with clouds and a 99% chance of rain projected.

Still, the desire to take advantage of such a rare occasion was palpable.

“I don’t know how to explain it to people,” said Collins. “There’s just something magical about it.”

Part of it, certainly, is community; many of the photographers who gather to capture the event each year are well-acquainted, with the evening sunset doubling as a social gathering.

And despite all photographing from the same location, the resulting photos often differ greatly in style. (The hashtag #phillyhenge features countless photos that have amassed thousands of collective views.)

“It’s just cool that so many people can come together and share and experience it,” said Kim Slouf, 42, an amateur photographer from South Philly who has been photographing Phillyhenge for at least the past five years. “It doesn’t matter you who are, what you look like, what your background is — you’re all just experiencing this really cool moment together.”

If, of course, the weather holds up.

“It’s very pretty if — pun intended — the stars align,” she said.

On Saturday night, Derrick Thomas, a Philly-based landscape photographer, arrived at City Hall armed with a pair of high-quality cameras and a good deal of optimism.

He’d captured countless sunrises and sunsets through the years, but this was his first attempt at shooting Phillyhenge from this location.

As evening traffic whirred past, Thomas set up shop on a sidewalk outside City Hall, positioning his Sony A7R5 atop a tripod and aiming it west down Market Street toward the horizon, where the sun was doing its best to fight through the cloud cover. He also wore his Fujifilm X-T5 around his neck.

And then he waited.

“One of the key tenets of photography is patience,” he said.

His weather app — TPE, or The Photographer’s Ephemeris — told him that sunset was slated for 7:28 p.m., and by 7:17, he was still feeling good, even as clouds continued to amass near the horizon.

“I’m optimistic,” he said.

But another five minutes passed, and then 10, and it slowly became clear:

Tonight was not to be.

Still, he didn’t seem overly deflated. How many times had he been brimming with anticipation to shoot some outdoor event or another, only to be foiled by inclement weather?

Maybe he would give it another shot on Monday, he said, when the forecast called for mostly sunny skies.

“That’s part of the journey,” he said, as he began to pack up his gear. “Sometimes, even if you don’t get the perfect shot, it’s just about being in the moment.”