When would the sky appear red instead of blue?
Sacatering of light:
Let be considered as the probability of scattering and is the wavelength of radiation, then it is given as:
3. Thus, the probability of scattering will increase for a shorter wavelength as it is inversely proportional to the fourth power of the radiation wavelength.
4. Since blue does indeed have a shorter wavelength whereas red has different wavelengths (longer), red is capable of reaching our eyes following air dispersion of light.
5. At sunrise and sunset, the Sun is very low in the sky, which means that the sunlight we see has traveled through a much thicker amount of atmosphere. Because blue light is scattered more strongly by the atmosphere, it tends to be scattered several times and deflected away in other directions before it gets to us. This means that there is relatively more yellow and red light left for us to see.
6. The diagram below shows that at midday, light has less atmosphere to travel through. Reaching Earth's atmosphere, it is scattered in all directions, therefore we see blue sunlight. Blue is scattered more than other colors because it travels as shorter, smaller waves. However, at sunset, light has further to travel through the atmosphere. The shorter wavelength of blue light is scattered further, as the sunlight passes over a greater distance, and we see the longer wavelength of yellow and red light.
Hence, during sunrise and sunset, the sky appears red.