Why sky is blue ?

The sky appears blue to human observers because of a process known as Rayleigh scattering. Light from the sun reaches the Earth's atmosphere and interacts with air molecules, which scatter the light in all directions. The blue color we see in the sky is due to the fact that blue light has a shorter wavelength and is scattered more easily than other colors in the spectrum, such as red or green. As a result, blue light is scattered in all directions and reaches our eyes from all around the sky, making it appear to be a uniform blue color.