Thank you all, again: ) I'm looking for some expressions to describe that when people see the blue sky, think the sky is so beautiful. Maybe it doesn't need too academic.

The name for the feeling you get when you look at the sky, or magnificent natural view, is "awe." It's the sound you make if your mouth is wide open! Now that I've written my answer I'm going to check a dictionary website: "A feeling of respect or reverence mixed with dread and wonder, often inspired by something majestic or powerful."

I think that is very subjective, and would have many different answers, unless the person were a meteorologist. Then he would describe the type of clouds, and the distribution of them.