Atmospheric perspective covers two ideas that help artists create the illusion of depth. First, the atmosphere - a mixture of dust and moisture in the air - scatters the sun's light rays. Blue light penetrates the atmosphere most easily, making the sky appear blue. It also makes things in the far distance appear bluish. Second, our eyes can only focus so far into the distance. Things very far away appear blurry and less distinct to us. When these two ideas are used together in a painting or drawing they tell your brain that an object is extremely far away. Its a great way to create the illusion of depth or 3-D.