The Romans referred to it as the “nocturnal sun”. Later accounts describe it as an unexplained glow – bright enough to read a book by – that would sometimes light up the night sky.
Now, researchers in Canada say ‘zonal waves’ in upper atmosphere may explain why people have reported oddly well-lit evenings since Roman times.
Researchers from York University in Canada have come up with a possible explanation for the rare phenomenon known as “bright nights”. Using satellite data, the scientists suggest that the bright nights are not due to the sun or meteors, but instead the result of converging “zonal waves” in Earth’s upper atmosphere.
Nocturnal Sun phenomenon
Accounts of the phenomenon are sprinkled throughout history. In the first century BC, Pliny the Elder wrote of an event that gives an appearance of day during the night” Subsequent accounts were published in 1783 and 1908.
But today, in the age of artificial light, this phenomenon, none of the modern researchers have ever seen “bright night” with their own eyes, which gave rise to legitimate doubts about their real existence.
Rare Bright Nights explanation
In 1991, Shepherd built a satellite instrument capable of measuring airglow, which results when ultraviolet radiation from the sun separates molecular oxygen into individual atoms. The atoms recombine at night, once the sun disappears, releasing energy that emits a green tint.
At times, airglow can be seen by the naked eye due to the fact that wavelengths in the upper atmosphere were at times superimposed over each other, brightening the airglow by as much as tenfold.
Their analysis showed these bright nights occurred 7% of the time and were highly localised, confined to an area about the size of Europe. But outside of remote areas, chances of seeing an event nowadays are slim, due to widespread light pollution.
Since the study was published, many whose families had passed down stories about experiencing the bright nights. One shared his grandfather’s story of being chastised as a child after accidentally staying out until midnight playing football, a story Shepherd chalked up to bright nights.
Bright nights: scientists explain rare phenomenon of ‘nocturnal sun’