The lady on the altar of the Basilica in Knock is annoyed. "The tabernacle is here. Stop talking," she yells.

Dressed in a pink jacket and a long black skirt, she's leading a rosary of 4,000 (apparently) pilgrims all come at the behest of clairvoyant Joe Coleman to see an apparition of the Virgin Mary in the Basilica at three o'clock on Saturday 31 October. Not everyone is on their best church behaviour. Children are screaming, some teenagers are chatting on mobile phones and some people have replaced the old tradition of silent prayer with conversation and untraditional bursts of applause.

There's a core of people closer to the altar who're praying intently. Joe Coleman is at the heart of these, pressed up to the altar with his eyes closed and his hands pressed together. Then there are people following the rosary. Out in the outer rings where I'm standing things are a tad more informal.

"Is Mary appear-ing here or what?" says a surly teen very loudly amid a throng of other surly teens. "Where is she then? And what's that wan doing?" he asks gesturing towards the praying lady. "For f**k's sake."

It's a strange kind of holiness, really. As the clock ticks towards 3pm (the time of the apparition, according to Coleman and fellow mystic Keith Henderson) the tension builds. People get slowly more silent and the lady on stage and Joe Coleman sneak quick glances at their watches. Men at the back of the crowd lift children up on their shoulders.

At the allotted time there is no grand revelation. But people stare more intently at the stage and more intently at Mary's representative on earth, whose hands part as she smiles and laughs and seems to see something. Most people around me are a bit disappointed.

"Oh, look, did her face just glow red!" says an excited lady behind me. "That's just a camera flash ma," says her son.

People really want to believe.

"I think there is something in Knock alright," said Tina from Donegal. "But whether it's appearing now or not is another matter. I'd love to see something, but I'm a doubting Thomas. I'm religious but this would make believing easier. It would make living a lot easier, to be honest, if you knew there was a hereafter."

Others are more sceptical. Mary, a regular pilgrim from Galway, didn't even know about the supposed apparition today. She's here with her sister, Carmel, and brother, Seán. "I take a scientific view," he says. "We were even checking around for projectors there earlier."

Right now, I'm guessing, Coleman is wishing he had installed projectors. Disappointment is spreading through the church. But then, suddenly there's a shout, and a stampede of men, women and children are running towards the exits. Out in the car park and around the grotto people don't know which way to look. The sun looks lovely. Some people are looking at that. Others are looking everywhere else but that. Apparently the sun is the apparition, although it just looks like the sun to me.

"I saw," a lady called Bridget Connors says adamantly in a soft voice. "It was the sacred heart and the virgin mother and it was absolutely beautiful."

Seán, the sceptic who'd been searching for projectors, seeks me out. "Would you believe I saw it," he says. "We all did. The sun was dancing around in the sky and there was a wash of colours. I'm a scientific man but I can't explain that."

Others aren't so lucky. "People believe what they want to believe," says a local lady called Helen. "I really came along to see all the people."

"I saw nothing," says a young boy sadly.

"What?" asks a man who happens to be passing. "Did you not see a perfect ring of pink around it?"

"Oh, I saw that," says the boy, a little disappointed, before brightening up: "Will she still be appearing in the church?"