Norwegian scientists have put forward a new theory to explain the inspiration behind one of the most famous works of art ever produced.
The Scream (1892), by Edvard Munch, depicts a figure holding its face, which is making an agonised expression.
But look above this individual and the sky is full of colourful wavy lines.
The researchers say these are probably Mother of Pearl Clouds - rare phenomena that would have had a big impact on anyone who saw them for the first time.
"Today the general public has a lot more scientific information but you can imagine back in his day, he'd probably never seen these clouds before," said Helene Muri from the University of Oslo.
"As an artist, they no doubt could have made quite an impression on him."