IN THE millennia before street lights and smartphones, humans could, on rare occasions, walk around on a moonless night and see clearly. Looking up, they could see broad luminous patches of light stretching across the sky, which brightened the heavens in all directions as though it were daylight. People could read without candlelight, view small details in their surroundings, and make out landscapes in the distance. It was as if the world were illuminated by a hidden night-time sun.
The existence of bright nights is well accepted, but their cause remains a mystery. Frustratingly, sightings have almost entirely faded away in the past few decades, making it seem that any hope of solving the riddle was dimming. Now, though, one man says he has seen the solution.
The earliest account of a bright night comes from Pliny the Elder, a Roman army commander who studied nature in his spare time. In his encyclopaedic Natural History of around AD 77, he wrote that the “phenomenon commonly called a nocturnal sun… a light emanating from the sky at night” has been seen many times. In 1988, a French atmospheric scientist named Michel Hersé produced the definitive collection of accounts of bright nights, which documented similar stories from the past millennium and all over the world. In French, they were nuit claires, and in German helle Nächte.
But sightings have become rarer. The most recent may be from 22 and 23 August 2001 at the Leoncito Astronomical Complex high in the Argentinian Andes. During that event, Steven Smith of Boston University in Massachusetts and his …