We start by retrieving the noise value from the noise texture (the noise variable). The green channel contains two octave noises, so we use the value stored in that channel (noise.g). Feel free to try out other channels and determine what looks right to you.
We use a cosine function to make a sharper transition between the cloud and sky color. The noise value will be between zero and one, and the cosine of that value will range between -1 and 1, so we add 1.0 and divide by 2.0. The result that is stored in t should again range between zero and one. Without this cosine transformation, the clouds look a bit too spread out over the sky. However, if that is the desired effect, one could remove the cosine and just use the noise ...
