Bright nights have bewildered humans since centuries but the details of its origins have always been a mystery for scientist, like some those mystically beautiful phenomena of universe. But they finally have an answer.

Humans are pretty jaded these days. We can write most of the strange phenomena we see off as science but it’s not just us, even the Roman philosophers like Pliny the Elder witnessed moonless nights glow bright like the day which surely makes an impression and the bright nights have been awestruck-ing us ever since. So basically, bright nights are when the night time sky is inexplicably bright enough to read a book by, even without moonlight for unknown reasons. But the scientists from York University in Toronto might finally have an answer.

They have observed what they call “enhanced airglow events” where elements in the night sky release photons. They know what’s causing airglow in their satellite data. But now they think they’ve figured out what enhances the glow, which may have caused the brighter nights documented throughout history. And their study suggests the effect is created as slow-moving, high-altitude atmospheric waves merge together and amplify the light from naturally occurring airglow, gas atoms that aren’t usually visible.

And the airglow is formed by various chemical reactions taking place in the upper atmosphere, including the green tinge in the air that happens when oxygen molecules split apart by the Sun join together again. And based on the data, bright nights only occur once a year in the places where they are noticeable, and you’d need a clear, moonless night to be able to tell the difference with your own eyes. So the scientists think that for every 7 nights out of 100 there’s a bright night somewhere on Earth. Although this might not be a life-changing research and won’t matter to most of us, it’s perhaps worth thinking about if you’re ever a long way from civilisation and notice the night time light is stronger than it should be.