When the sun is about to rise over a ridge that’s pretty high and there are diffuse clouds a little higher and closer than the ridge, and if it all comes together just so, the sun will cast a silhouette of the ridge line against the clouds. Sometimes the silhouetted peaks lie behind the first ridge, in which case the sun is projecting an image of something that would be invisible otherwise.
It’s not a particularly rare phenomenon, but you need to pay attention or you might miss it. Here are a few Himalayan examples from my photo archive. I suppose mountain ranges in other parts of the world might show this phenomenon too. Does anyone have any examples?