Hello friends, to answer the question that why sky appears Red during sunrise and sunset, let us read the previous article that is why sky appears blue to understand the basics of light travelling from Sun. We have discussed about the light travel in form of waves and it passes through atmosphere surrounding our earth. The white light splits into 7 colors.

As white light from Sun consists of seven colors. Exactly, you are right that is the color of Rainbow that is VIBGYOR. You must have seen the same during experiment with Prism. If not try to do it.

You will see Violet, Indigo, Blue, Green, Yellow, Orange and Red that is VIBGYOR.  

The wavelength of these colors vary from 4000 angstroms to 7000 angstroms. 4000 is of Violet and 7000 is of Red. It means the Violet is the shortest wave or we can say that it has shortest wavelength and Red has longest wavelength.

Now come back to what is the role of air particles consisting mostly of nitrogen and oxygen, dust particles or water droplets in appearing the color of sky blue. The air molecules are smallest in size and these molecules will scatter the shortest color or wavelength of light easily that is violet, indigo and blue. But violet is not so bright color and percentage of violet is very low in sun light also and indigo and blue after scattering mixes and give the bluish color to sky after scattering .

This is also proved by Rayleigh Scattering which shows that scattering is inversely proportional to (wavelength)⁴.  It means lesser the wavelength; more will be the scattering. That is case with blue color.

During sun rise and sun set, the Sun is at horizon of earth that is much farther away from earth (please refer figure). Thus sun light travels the maximum distance during sun rise and sun time. Of course blue color scattered much more due to reason already discussed, but as sun is farther away thus blue also go away farther after scattering or more precisely Rayleigh Scattering during sun rise and sun set.

Therefore the color like orange and Red easily passed through the atmosphere as these are least scattered. In the above diagram sun is at top not at horizon but during sunrise and sunset, sun is at horizon and light has to travel maximum distance. Thus the blue light scattered but remains farther away but red light least scattered reaches our earth easily. This is the reason that during sun rise and  sun set the sky looks Red. The reason of sky is blue at day time and red during sunset and sunlight is explained by metoffice.gov.uk also.

This is the reason that sun and sky looks Red during sunset and sunrise time.