at sunrise and sunset sun looks red  due to red has high wavelength and also large distance from harizon but  at afternoon  sun looks bright. But sun is stationer then why sun looks red at sunrise &sunset

Hi,

At sunrise and sunset, the intensity of sunlight for equal angle of elevation of sun w.r.t the horizon, is same. At the sunset and sunrise rays have to travel a greater distance to the surface of earth because of the slanting rays of sun, thus other colors are scattered away in the upper atmosphere but red color having longest wavelength is the least scattered and the sky appears reddish. This phenomenon is called atmospheric refraction

No doubt the sun is considered to be stationary but the earth is rotating as well is revolving around the sun. The rotation of the sun around its axis causes the apparent elevation of the sun at different time of the day.