What happened
Residents on both banks of the Mekong have told for generations of fireballs that shoot up from the river and vanish at a height of several hundred meters. They are said to appear in the greatest numbers on the night of Wan Ok Phansa, which marks the end of the Buddhist Lent, usually in October. According to local belief, they are a gift from Phaya Nak, a great serpent that lives in the river. Until the mid-1980s they were called “ghost lights”; then local authorities gave them an official name, and a festival grew up around the phenomenon, drawing crowds of spectators to Phon Phisai District. Accounts speak of dozens, and sometimes thousands, of balls in a single night along a stretch of the river about 250 km long. In 2002 a report by iTV sparked a nationwide debate in Thailand about the origin of the lights.
Witnesses
Residents of the Thai and Lao banks of the Mekong, pilgrims, and tourists; the phenomenon has been filmed many times by television crews.
Explanations and hypotheses
The 2002 iTV report showed Lao soldiers on the other side of the river firing tracer ammunition, and Thai biologist Jessada Denduangboripant, after analyzing the footage, concluded that the balls were flares being launched. A natural explanation has also been proposed – spontaneous ignition of phosphine and methane from river mud – but critics point out that gas bubbles could not glow like this or rise so quickly. For many local residents, the phenomenon remains above all a religious sign.
Disputed A likely explanation exists, but some of the facts are still disputed.
More: Wikipedia (en)