The
sunlight while travelling through the
atmosphere is broken up and scattered by the tiny particles of air,water and water vapours and dust and makes the
sky looks blue. As we know , sunlight is made up of seven colors and it travels in waves. Light of different colors moves in
waves of different lengths. The waves of
blue are much
shorter than the waves of red or
orange light . As the sunlight pass through the atmosphere , the waves of blue light are just of the right size (shorter waves) to be broken and scattered by the air, watervapour and dust particles, and then they are spread in all directions, while the waves of red and orange lights pass right through the atmosphere and reaches our eyes. This scattering of blue light makes the sky appear blue. However in the morning and evening, i.e, the time of sunrise or sunset , the light from the sun passes through the greater layer of the atmosphere that scatter the orange and the red light waves as well . Thus the sky looks a red or orange color at that time.
More abstracts about the Why does the sky appears to be blue?