Tofo is a curve of white sand and coconut palms on the Inhambane peninsula, five hundred kilometres up the coast from Maputo, known for whale sharks, manta rays and having almost nothing in the sky. There is no airport nearby worth the name, no weather station, and no air traffic. People go there to look at the sea, and in 2009 a small business there had a habit of taking a photograph every morning to post to its page for the folks back home.

On 1 July 2009, sometime between seven and nine in the morning, they took the usual pictures and thought nothing of them.

A fortnight later somebody was scrolling back through the folder looking for a particular shot and stopped. In one of the frames from that morning were two golden shapes in the sky, somewhere between triangular and round. One of them appeared to have a halo around it. In a second frame from the same morning the two shapes were still there, but blurred into golden smears, as if they had moved between exposures.

The writer’s first thought was the lens, so they checked. Photographs taken immediately before and after that morning, on the same camera, showed nothing. Whatever the shapes were, they were in the sky over Tofo for a few minutes on the first of July and not at any other time. Nobody on the beach had noticed anything. Nobody had looked up.

Baffled, they wrote to the American reporting centre NUFORC and asked, politely and rather urgently, for an explanation. The report is signed off with their name removed and a request for a soonest reply. There is no record of one.

This is a species of sighting the archive will see again: the photograph that shows something nobody saw. It has a specific set of explanations, all of them dull and one or two of them quite likely. Sunlight striking the front element of a lens at a shallow angle produces internal reflections, and those reflections are typically golden, geometric and haloed, and shift between frames as the camera moves a fraction. A morning shot across a bright sea, with the sun low in the east, is the textbook condition for it. The fact that other frames are clean is not the alibi it seems, because flare depends on the exact angle to the sun, and a slight turn removes it entirely. Two birds, a drop of sea spray on the glass, or a pair of distant kites can do the rest.

Against that: the writers knew their camera, had hundreds of comparison frames, and were clearly not people who wanted to see something. They were, if anything, annoyed.

The photographs have not surfaced online, or at least not anywhere the archive has found them. Somewhere there is a folder from a Tofo morning in 2009 with two golden shapes in it, and a manta ray or two, and the people who took it still do not know what they photographed.