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Why do we observe difference in colors of the sun during sunrise, sunset and noon?
The sun and the surrounding sky appear red at sunrise and at sunset because at that time most of the blue colour present in sunlight has been scattered out and away from our line of sight,leaving behind mainly red colour in the direct sunlight beam that reaches our eyes.This can be explained as follows:

At the time of sunrise and sunset when the sun is near the horizon,the sunlight has to travel the greatest distance through the atmosphere to reach us.During this long journey of sunlight,most of the shorter wavelength blue-colour present in it is scattered out and away from our line of sight.So,the light reaching us directly from the rising sun or setting sun consists mainly of longer wavelength red colour due to which the sun appears red.Due to the same reason,the sky surrounding the rising sun and setting sun also apper as red.Thus at sunrise and sunset the sun itself as well as the surrounding sky appear red.


When the sun is overhead (as at noon),then the light coming from the sun has to travel a relatively shorter distance through the atmosphere to reach us.During this shorter journey of sunlight,only a little of the blue colour of the white light is scattered (most of the blue light remains in it).Since the light coming from the overhead sun has almost all its component colours in the right proportion,therefore the sun in the sky overhead appears white to us.


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