On a clear sunny day, the sky above us looks bright blue. In the evening, the sunset puts on a brilliant show of reds, pinks and oranges. Now the question is why is the sky blue? And what actually makes the sunset red?
Well, the blue color of the sky is due to a term called Rayleigh scattering. As the light moves through an atmosphere, most of the longer wavelengths pass straight through. The air affects little of the red, orange and yellow light.
Nevertheless, the gas molecules absorb much of the shorter wavelength light. The absorbed blue light is then radiated in different directions. It gets scattered all around the sky. Whichever direction you look, some of this scattered blue light reaches you. Since you see the blue light from everywhere overhead, the sky looks blue.
As you look closer to the horizon, the sky appears much paler in color. To reach you, the scattered blue light must pass through more air. Some of it gets scattered away again in other directions. Less blue light reaches your eyes. The color of the sky near the horizon appears paler or white.
Also please note that out in the space, our sky does not look blue instead looks dark and black. This is because there is no atmosphere in the space and no scattered light to reach our eyes.