Saturday night at the end of November, Long Street at full volume, the mountain a black wall at the end of every side road. Somebody looks up between the bars and sees that the low cloud over the city has a green light in it.

Within an hour the photographs were everywhere. A hard, unnatural green glow, sometimes a patch, sometimes a beam, moving slowly across the underside of the cloud above the city bowl. People photographed it from Long Street, from balconies in Tamboerskloof, from the Foreshore. A hashtag went up and trended nationally. Then, because the internet is the internet, people in Durban and Johannesburg said they had seen the same green light over their own cities that evening, which either made it a very large phenomenon or a very ordinary one.

By Monday the newspapers had gone looking for an answer and come back with two that contradicted each other.

The South African Astronomical Observatory told News24 that, from what it had heard on the radio that morning, the light was a test of the show equipment at Cape Town Stadium, which was gearing up for a big rugby weekend a fortnight later. That is a perfectly good explanation: a powerful moving-head light aimed into low cloud paints a bright spot on it, and green is what a lot of stage lights do best.

Then the paper rang the stadium, and the stadium referred them to the rugby union, and the rugby union’s spokesman said, with some care, that they knew of no light equipment test on the Saturday in question. It was probably, he offered, some kind of marketing campaign, but not one of theirs.

At which point the rugby tournament’s own social media account posted that a UAP had been seen over Cape Town and that the world was coming, and to meet the welcoming committee. The spokesman, asked about that, called it ambush marketing: someone jumping on a story, not owning it. He was not wrong. But it did rather muddy the water.

That is where the trail ends. No company ever put its hand up. The observatory’s stadium theory stayed second-hand. Nobody produced a lighting rig, a permit, or a technician who had been on the roof that night. The green light did not come back.

Cape Town has a long relationship with strange things over the mountain. The lenticular clouds that form in the lee of Table Mountain in a south-easter are photographed every summer as flying saucers, and every summer somebody has to explain them again. The city’s own light pollution, bounced off low cloud, produces glows in every colour the sodium lamps and LEDs can manage. A laser from a club roof, a searchlight from an event, a green navigation light on a helicopter in cloud, a police spotlight: any of them could have done it, and none of them was found.

What remains is a Saturday night, several hundred phones pointed at the same cloud, one official explanation withdrawn by the people it named, and a rugby tournament happy to take the credit without the blame. Cape Town, in other words, being Cape Town.