Last year, in an unlikely development, I was booked to DJ at Glastonbury Festival. When I arrived on Thursday afternoon, one thing struck me straight away.

There was a very particular atmosphere. I'd best describe is as a sense of release – of a wait being over. I'd never seen or felt anything like it.

That Thursday feeling stayed with me. I kept thinking about it in the months afterwards

Though the main stages open on Friday and run all weekend, Glastonbury is a five-day festival.

To its organiser, Emily Eavis, the first two days are special. The festival was started by her parents, Michael and Jean, and her memories are intertwined with family life.

"Traditionally, it would be me and my dad who go down to open the gates on Wednesday," she says.

"It's like letting people into Christmas in a way, you know? It's sort of like musical Christmas, because they're in the best state of mind."

Over the next two days, the site fills up. And, at some point, almost everyone is in.

"Normally Thursday afternoon is when we reach capacity," Emily tells me. "I get a message when we know that the site is full.

"I love the Thursday. I love energy of the Thursday."

She then describes the same phenomenon I noticed last year.

"There's a palpable feeling of excitement, anticipation. People want to see everything and touch everything and be there together. It's a feeling of community, and big gangs of friends all reuniting.'

"A palpable feeling of excitement," is the perfect way of putting it.

The opening of the festival is something Emily has been witnessing her whole life - although it predates her by 10 years.

In 1970, her farmer parents organised the Pilton Pop, Folk and Blues Festival, with glam rocker Marc Bolan, '60s pop star Wayne Fontana and singer-songwriter Al Stewart playing in his back garden.

"I think this is the quickest way of clearing my overdraft," said Michael, when asked why he was staging a concert in the field where his dairy cows typically grazed.

With a few fits and starts, that event went on to become the UK's most recognisable music festival.

And while it has changed over the years, some things have stayed the same.

'When I was little, it was very different to how it is now because it was so much smaller, it was a very few people," says Emily.

"But they still had the same look in their eyes which they have now, which is cheer, determination and commitment and joy and excitement and kind of magic.

"The look of, like, they're going to make this five days the best five days of their life and it's an amazing thing to witness."

It was an amazing thing to witness first-hand last year. And as Emily once more sees the valley fill up, to my delight, I'm one of those who's pitching their tent.

I'll be DJing at Stonebridge on Thursday night and doing my best to capture the sense of expectation and possibility.

To do that, I've been getting some help from Radio 1's Greg James and his listeners – and from Drum & Bass DJ and producer Crissy Criss.

Last week, I took the lift from the BBC newsroom all the way to the top of London's Broadcasting House and joined Greg on his show.

We talked about Glastonbury – and Greg asked his listeners to send us voice notes describing the way they feel as the festival kicks off. A good number of them did.

We then sampled some of those messages – alongside my interview with Emily Eavis.

Crissy Criss has scattered those samples across a track that's a celebration of what Thursday at Glastonbury is all about.

Greg will introduce the track at the Stonebridge venue where I'm DJing.

As you can probably tell, that Thursday last year had quite an impact on me.

As one of Greg's listeners put it: "You set yourself up, you've got your drink. Life is good. You are where you're meant to be."

Or in the words of Emily Eavis: "They're going to make this five days the best five days of their life."

The BBC has extensive coverage of the festival over the next few days on TV, iPlayer, radio and BBC Sounds.