(Credit: Tim McDonald)

The last daring lingerers scurry clear as a fizzle becomes a roar. A bright cone of flame bursts from the bottom of the rocket, which is a long piece of pipe packed with homemade gunpowder. As smoke billows, the rocket lifts off, slowly at first, but gathering pace as it clears the launch frame.

The rocket whips skyward, its trail twisting as it gains altitude. On the ground, the atmosphere is electric. With eyes towards the heavens, the crowds point, throw their fists in the air and cheer as the smoke envelopes them. The team that launched the rocket hug and high five. The drinks flow. Nobody seems to know or care where the rocket landed – or if even any part of it survived.

Rockets reach for the heavens all day, with crews lifting them onto massive launch platforms, and sending them skyward. This is the culmination of the Thai city of Yasothon’s Bun Bangfai, or rocket festival, which takes place each year in early May. Yasothon hosts the biggest festival in Thailand, but it’s celebrated across the country’s north-east and in neighbouring Laos. It seems like a pyromaniac’s dream, but it’s also a celebration that taps deep into local legends.

(Credit: Tim McDonald)

This is an ancient tradition. After rockets are launched into the sky, then it rains. Our ancestors have conducted this tradition for 100 to 200 years,” said Pimay Chokehana, a local rocket maker.

(Credit: Tim McDonald)

Bun Bangfai is a folk tradition mostly practiced by Lao people in the Isan region of Thailand and in Laos itself. The legend behind it seems to vary slightly with each re-telling, and although it changes from community to community across the region, the fundamentals remain the same.

All the land-bound creatures decided that Phaya Khang Khok, the Toad King, was the most righteous being in the universe and the most legitimate ruler. This upset a jealous Phaya Thaen, the King of the Sky, who baked the earth dry. At first the Naga, a dragon-like serpent, took on the Sky King, but was vanquished in battle. He convinced the Toad King to lead the earthbound creatures in a second assault. After a ferocious battle, Phaya Thaen eventually came down to the ground and the Toad King pushed for peace. The rockets aren’t so much a re-enactment of the battle as a reminder to Phaya Thaen to fulfil his obligation to bring rain.

The festival merges elements of Buddhism and local traditions that predated Buddhism’s arrival in the region. There are some who believe the Toad King is a previous incarnation of the Buddha.

“Virtually every festival in Thailand is some merging of the two. Unlike some of the Abrahamic religions, Buddhism doesn’t say ‘this must go’. It tends to appropriate and incorporate,” said Andrew Johnson, an anthropologist specialising in Thai religion and a visiting fellow at Cornell University's South-East Asia Program.

(Credit: Tim McDonald)

The festival gets into full swing with a huge street party. A few prepare for the following day’s parade with some last-minute dancing practice in Yasothon’s old town (pictured). Nearby, the main street is lined with dozens of stages that were hastily assembled the previous day.

Various groups set up along the main road, each with a bone-rattling sound system to compete with their neighbours. For some, it is karaoke with friends, while others have full bands or dancers. In all cases, it is a deafening, booze-fuelled celebration that lasts all day.

An estimated 100,000 people attend the festival, but they’re spread throughout the town so it doesn’t feel too claustrophobic. And there are quieter celebrations in the town’s backstreets; sometimes half a dozen people will set up a small stage at a shop or a house. It doesn’t always take a huge crowd to celebrate. People are friendly, and visitors can expect to be invited on stage. It doesn’t seem to matter if you don’t know the songs or even the language in which they’re sung.

(Credit: Tim McDonald)

The second day of the festival is the parade. Floats representing surrounding villages and temples amble down the main thoroughfare. Covered in wooden panels, they’re staggeringly rich with detail. The Naga features on many of the floats, and each carries a bangfai (rocket), although these ones are purely decorative, recalling the days when they were made of bamboo. Nowadays, the rockets are far more likely to be made from plastic piping, which Chokehana says is safer and flies better.

The floats are so big that two men walk in front of each one and have the worrying task of using a long pole to lift a tangle of power lines over the highest point, which is often the bangfai itself.

(Credit: Tim McDonald)

The parade day is a slightly more formal affair than the street parties. Even so, it’s full of variety, with all kinds of performances. Dance troupes and floats pause in the main square, where crowds watch from stands and an announcer introduces them while VIPs look on from a booth. Groups walk down the street carrying banners, and farming communities load traditional agricultural gear onto their floats. There are beauty queens. There’s a maypole. A group of transgender dancers wearing carnival-style outfits (pictured) pauses for pictures with the crowds. The entertainment is seemingly endless.

(Credit: Tim McDonald)

Palai Tip is one of 60 dancers in her troupe. All are resplendent in yellow, denoting Monday, which is the day on which the newly coronated Thai king was born. The group moves in synchronised steps, shuffling, turning, bending and standing to attention, bending their fingers back from extended arms.

“I love Thai dancing,” she said, explaining that it’s good exercise and good for posture.

The dancers are backed by bands of drummers and musicians playing the phin , a local stringed instrument . They move through several numbers, each with twangy melodies over a lurching rhythm. Then they march from the main square down the street, where they get closer to the crowds who are overflowing from the footpath.

(Credit: Tim McDonald)

Bun Bangfai is a loud, raucous celebration. On launch day, a few daredevils cluster by the launch towers, erupting into cheers for each rocket. Small children cover their ears. Bands playing on a nearby stage get drowned out every time a rocket lifts off.

Thousands come to watch, mostly sitting on the grass or rocks at the edge of the lake. A few spectators set off their own smaller rockets. Some even hold them in their hand, only throwing them skyward once the fuse hits the powder.

There are a few comedic elements to the festival, too. Most of the crowd blocks out Phaya Thaen’s baking dry-season sun with umbrellas. But a few take it a step further, cooling off in the mud and often covering themselves from head to toe.

(Credit: Tim McDonald)

Chokehana and his workers load several rockets onto the back of a pick-up truck and drive to the launching grounds. They make some final preparations, adding decorations, wrapping the rockets in foil and packing the gunpowder more tightly.

Chokehana lights some incense and prays by a tree before a group of men lift the rocket onto their shoulders and carry it to the launch towers, a few of them being far too cavalier about the distance between their lit cigarettes and the giant tube of gunpowder on their shoulders.

The men use ropes to haul the rocket up onto the large wooden launch frame. They abandon it temporarily for a launch from an adjacent frame, but return and hook it into place. They clear out of the danger area as the countdown inexorably heads towards blast off.

(Credit: Tim McDonald)

Throughout the day, rockets shoot high into the air while the crowds cheer on. It’s not unheard of for rockets to explode on the frame (visitors should put a healthy distance between themselves and the rockets as there have been deaths and serious injuries at these festivals). This year, a few don’t take off as planned, but most go off without a hitch, and there are no explosions.

It’s a great spectacle, and Chokehana says he loves a good launch.

“I am really happy and about to dance,” he said.

(Credit: Tim McDonald)

Bun Bangfai is loaded with important symbolism, within which are layers of meaning. As well as initiating the rainy season, this is a fertility festival, with phallic rockets impregnating the sky with life-giving waters.

But Bun Bangfai is an underdog story, too. Yasothon is far from Thailand’s centres of economic and political power. Locals here regard themselves as honest and genuine. So, there’s clearly symbolism in an ugly toad taking on the Sky King, or the farmers themselves menacing the sky with rockets, according to Johnson.

“You really can’t help but to see the victory of the lowly farmer over the powerful distant overlord,” he said.

This year it wasn’t much of a struggle to get water out of the sky; the rain came before the first rocket was even launched. As the surrounding villages geared up for more celebrations the following weekend, more than a few locals would have been pleased at the sight of their rice paddies turning greener.

Why We Celebrate is a BBC Travel series that revels in how a festival or event is intertwined with a place’s culture.