The sun appears red at sun rise or sunset, why?

Explanation

Sun becomes visible earlier to actual rise, due to refraction

when the sun is just below the horizon, it is not visiblke to us but due to refraction of light from atmosphere a virtual image is formed just abvoe the horizon, so the sun becomes visible to us. Otherwise actual sun will take two minutes to come above the horizon. So sun becomes visible two minutes earlier than actual rise. Similarly in the evening sun remains visisble for two minutes even after set. So the length of the day becomes four minutes more than it actual length.