When light comes from the sun, all these light waves of different wavelengths travel through empty space. When they reach Earth’s atmosphere, the light waves can interact with particles in the air like dust, water droplets, and ice crystals. Because of the extremely small size of visible light waves (less than one millionth of a meter), these light waves also interact the tiny gas molecules that make up the air itself. The light waves bounce off these particles just like you might bounce and get jostled in a busy hallway. As the light waves bounce in lots of different directions, we say they have been scattered.
In the air ,part of the sunlight is scattered.the small particles {molecules,tiny droplets of water,dust particles }scater photons the more,the shotter the wave length is .Therefore,in the scattered light ,the short wavelengths predo yminate,the sky appears blue,while direct sunlight is some what yellowish or even reddish when the sun is very low.Goethe believed this is to be the basic phenomenon to generate colours ("uraphanomen")

due to the scattering of the light  the wood in the background is seen like behind a  bluish veil .

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