Scientists may have discovered the reason why the phenomenon of “bright nights” pepper historical accounts since Roman times.
Once in a while, in the past, bright nights would occur. During these nights, the skies glowed. It was bright enough outside and you'd be able to read a book simply by the light in the sky. There have been a number of accounts pertaining to this phenomenon throughout history. Pliny the Elder mentioned the phenomenon in the first century BC. He wrote: "The phenomenon commonly called 'nocturnal sun', i.e. a light emanating from the sky during the night, has been seen during the consulate of C. Caecilius and Cn. Papirius (~ 113 BCE), and many other times, giving an appearance of day during the night." There were also accounts of the same phenomenon in 1783, 1908, and 1916.
Unfortunately, it's possible that only a few people alive have ever seen a bright night. In fact, it's also possible that no one alive today has ever seen the phenomenon.
The reason we don't experience the phenomenon anymore may be the same reason it can be difficult to see the stars: light pollution. However, this doesn't mean that the phenomenon doesn't happen anymore. They can still be observable by scientists, and may still be visible in remote places.
Of course, the big question is what causes this phenomenon. Researchers have found that amplified airglow may be the cause of bright nights. Airglow, which we normally aren't able to observe, is a faint light in the sky at night. It may sometimes take on a green tinge due to oxygen in the atmosphere. When wave frequencies in the upper atmosphere align and converge, the effect amplifies airglow. Up to four frequencies can come together at a certain location, and this is what induces a bright night.
Scientists have been studying airglow for a long time. They estimate that airglow probably occurs about 7% of the time, which means that it isn't as rare as it may seem. However, the moon and bright artificial lights can render airglow and bright nights invisible to the naked eye.
Strong storms are also able to make the occurrence of a bright night more likely. However, this still won't make it likely for a lot of us to witness a bright night. Since many around the world live in urban areas with a lot of light pollution, there's a chance that we'll never see the night sky glow. It was easy for people in the past to witness a bright night since there were no artificial lights to compete with the glow in the sky.
This, of course, is regrettable, especially since bright nights still do in fact occur. Our satellites can detect them, though our eyes alone can't. Maybe, someone lucky will trek out to the wilderness, far away from lamps and halogen signs, and be able to witness a bright night. It'll be certainly something quite amazing to tell your kids and grandkids about.
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