When the sun is near the horizon during the morning or evening, it appears reddish. The phenomenon that is responsible for this observation is scattering of light. During sunrise and sunset, the sunlight has to travel a larger part of the atmosphere because they are very close to the horizon. Therefore, light other than red is mostly scattered away because of their short wavelength as light having shorter wavelength cannot travel longer distances. Most of the red light, which is the least scattered due to its long wavelength, enters our eyes. Hence, the sun and the sky appear red due to scattering of light. It should be noted that during sunrise and sunset, sun appears bigger in size due to refraction of light.