Why does the sky appear blue

why does the sky appear blue

After seeing a clear blue weekend sky, while most of us plan a trip with family and friends, there are not many who think about why the color of the sky is blue and not red, yellow or green. Though it is one of the most basic questions that many people might have thought about during childhood, the answer is not as simple as the question itself.

The answer to this question lies in the atmosphere that surrounds the earth. As we all know, our atmosphere primarily consists of nitrogen and oxygen gases with oxygen making up for 21 percent of the atmosphere and nitrogen about 78 percent. Since sunlight, which usually appears white to us, has to travel through these gases before hitting our eyes, it scatters due to the molecules of gases in the atmosphere.

The blue color of the sky is precisely due to the Rayleigh scattering – the elastic scattering of light or any other electromagnetic radiation by particles much smaller than the wavelength of light. The exact reason is that a portion of the beam of light coming from the sun scatters off molecules of gas and other small particles in the atmosphere. This is the scattering that gives the sky its brightness and color.

The scattering or diffusion of light is inversely proportion to the fourth power of wavelength, meaning that the shorter wavelengths of light, including violet and blue, scatter more than the longer wavelengths  including red and yellow. Moreover, since our eyes are not that sensitive to violet color, and also because of the fact that violet scatters easily and far away from our eyes, we usually see the sky having a pale blue color.