It's all about the full moon, according to a female friend of Rolf Harris, who chatted to the Sunday Tribune over some local organic cider at Worthy Farm in Somerset.

The Glastonbury festival hadn't been held during a full moon for quite some time, the theory being it only rains in these parts after a full moon, which shone over the sprawling site last night.

"I've been watching the moon here for a while – if you watch it, you begin to understand why it rains."

"So, how long have you been watching the moon at Glastonbury?"

"Oh, since about '78, I think."

That's quite some time to be watching a moon at a festival, although not as aged as Rolf Harris himself, who cheerily galloped through his set on Friday morning.

"Glastonbury is 40 and I'm 80," he announced from the Pyramid stage, one of the few permanent structures on this usually soggy dairy farm owned by Michael Eavis, assisted by his daughter Emily.

A lot has changed since our moon-obsessed companion started staring at the sky here, and even more since the festival began 40 years ago.

In 1970, admission was £1 with unlimited free milk. These days, you can pay £5,000 (€6,000) to stay in a luxury tent with your own butler and guzzle champagne for the weekend. Or you could just hop the £1m security fence as three punks we met on Friday did, complete with replica campsite wristbands made from crisp packets.

The festival nervously kicked off on Wednesday as 50,000 people gathered in front of the Pyramid stage to watch England beat Slovenia, complete with several vuvuzelas.

By Friday, most of the expected 177,500 (not including 20,000 volunteers, a few thousand press and VIPs, and 2,000 bands and artists) had arrived.

For three days, Glasto becomes the third largest city in southwest England, generating over €100m for the economy.

Worthy Farm, which tucks its 300 dairy cattle away from the madness for a week, is at its peak in the sun, and boy, is it hot.

The infrastructure stats are remarkable: two million-litre underground reservoirs that provide the water, 4km of piping, a storage facility for two million litres of human waste, a kilometre of urinals and 1,600km of road.

Oh, and then there's the music. Northern Irish band Two Door Cinema Club were one of the first to play on Thursday with around 30,000 people turning up for their gig in the 2,000 capacity Queen's Head venue.

The following morning, award-winning Galway musician Julie Feeney opened the acoustic stage area.

The Gorillaz, led by Damon Albarn from Blur, disappointed as a headliner on Friday night, leading many to question how decent of a replacement they were for U2, who pulled out because of Bono's back injury.

This morning, all eyes are on Villagers, the project of Dublin musician Conor O'Brien as he plays The Park stage on a wave of critical acclaim for his debut album and live shows. Tonight, Stevie Wonder closes the festival.

Of course, Glastonbury is all about being diverted, and the diversions and distractions are endless. From solar-powered cinemas to a massive purpose-built tower block nightclub with a burning Tube train carriage on top, from a surprise visit by Prince Charles to outdoor circuses, from flame-throwing animatronic machine animals to the healing fields with their endless tents promising spiritual salvation.

Glasto is not so much a festival as a temporary city.

Vast, overwhelming and surreal, it's easy to get lost in more ways than one.

But if you do, just watch the moon.