What caused the blue lights in the sky?

Strange Blue Lights' Seen Over Arctic Circle Were Not Aliens, Says

Strange Blue Lights' Seen Over Arctic Circle Were Not Aliens, Says

What is that string of lights in the night sky?

Strange blue lights appear in skies across the world as sightings

Why Is the Sky Blue? NOAA SciJinks – All About Weather

Why Is the Sky Blue? - Owlcation

There's an explanation behind the mysterious glow lighting up the

What is the cause of a blue flash of light in the sky? - Quora

New York Sky Turns Bright Blue After Transformer Explosion - The