Our atmosphere is filled with dust and other aerosols whose sizes are comparable to the wavelength of blue light, about 4000 Angstroms, which makes them very effective in scattering light at these wavelengths. Towards a sunset, the blue component of the white light is scattered out of the light from the Sun and it appears red. As we look away from the Sun, the light we see in the atmosphere is the blue light component. This explains why sunsets are red, and why volcanic eruptions often produce spectacular crimson sunsets the world over. On clear days with little dust, however, the sky is blue because of the scattering of incident sunlight directly off of the numerous molecules of oxygen and nitrogen.