Why is the sky blue?

Getting right to the point :)

1. Light is divided into range. When it is refracted, it decomposes into seven colors (like a rainbow). This was first described in detail by Isaac Newton who passing white light through a prism.
2. The Earth's atmosphere does not lights itself. As the prism, it only refracts incident light. In particular, the sunlight.
3. The sunlight in the atmosphere interacts with air molecules.
4. Different colors in the spectrum have different frequencies. Blue has the highest frequence so we used to see the blue sky.
5. Sunsets and dawns can be red, yellow or orange. This is due to the deviation of sunlight. Blue light passes atmosphere and we see the lowest frequence ^^