Why does the sky change color? In the days it is blue while at sunset it looks reddish? Well, all particles in the atmosphere absorb and scatter light, and that is why we see color. However, not all wavelengths in the visible light spectrum scatter equally. Meanwhile,the light toward the violet end of the spectrum with shorter wavelengths (which has more energy) scatter better than those toward the longer, less energetic, red end. This tendency is due in part to their higher energy, which allows them to reflect and scatter around more. Besides that, Rayleigh's scattering model shows that the intensity of scattered light varies inversely with the fourth power of its wavelength, which means light with shorter wavelengths (such as blue and violet) scatter a lot more than long ones when particles are relatively small. The air is composed of oxygen, nitrogen, and other gas molecules, which are pretty small, aren't they? Under these conditions, scattered light also tends to disperse equally in all directions, and that is why the sky appears so saturated with color. So in conclusion, we get a saturated blue in the sky in the morning. The reddish sunsets is due mostly to the fact that the sunlight need to travel through more atmosphere to reach our eyes at sunset. The sun is not right above our head at sunset time. Instead, it is at the west side far from us, so the light is travelling from the west corner of the sky. By common sense in math, the hypotenuse is always longer than the other sides right? By the time the light arrives, lights with shorter wavelength (blue and violet in this case) have been scattered away, leaving only the longer-wavelength, direct illumination of sunlight’s redder tones, so we get a reddish sky.