One of the things I learned in my college Drawing II class and again in more depth in my Painting I college class is about aerial or atmospheric perspective. To be honest I never knew about it before although it's the way the human eye sees the world and I love it in photography and in drawings and paintings. I just didn't know its name or that it's a necessary art technique to use if you want your landscape to look realistic and right to the eye and mind.
There are two main components to aerial / atmospheric perspective: that the distant most part of a landscape has more blurry edges and is not as crisp as things in the foreground or middle ground and that in color works the color of the farthest away things is more gray or blue, cooler tones and not at all the same bright colors as the things in the foreground or middle ground. So a pine tree up close has bright green needles but the same variety of pine tree far away would be a different shade of green, more dull and grayish or bluish.
I was told that to not use atmospheric perspective is an amateur or newbie mistake and it reads so wrong to the eye and mind that it screams "bad art". I had never thought of it before but now when I see it I think to myself, "No! That is so wrong looking!"
I am so new to painting, having only done one landscape in trying to teach myself to do watercolor about five years ago. I am a newbie and am looking forward to learning how to choose correct colors and to make the farthest away things not crisp and sharp so it looks as we see a real life landscape with our own eyes.