Lord John Rayleigh (English physicist)
Light travels at the straight line as long as nothing
As it moves through atmosphere, it bumps into bits of
solid particles or gas molecules and becomes scattered
in all direction by either reflection or refraction.
The angle through which sunlight scattered varies
inversely to the wavelength.
Blue always scattered first and violet last.
Sunrise and Sunset (Red)
When sun is near the horizon or near the sky, sunlight
travels longer through the atmosphere before it gets to
your eyes. However, the blue light is unable to pass. It
becomes scattered in the atmosphere before even
reach your eye.
As light moves through the atmosphere, most of the
longer wavelengths pass straight through. However,
much of the shorter wavelengths interacts with gas
molecules and become scattered in the atmosphere.
Clouds in contrast to the blue sky appear white to
achromatic gray. The water droplets that make up the
cloud are much larger than the molecules of the air
and the scattering from them is almost independent of
wavelength in the visible range.