Blue sky and red sunset, illustration. Within the visible range of light, shorter wavelengths (violet and blue) are scattered by the atmosphere the most strongly. More blue light is scattered towards our eyes than other colours, causing the sky to appear blue when the sun is overhead. Red light waves are scattered the least by atmospheric gas molecules. At sunrise and sunset, sunlight travels a greater distance through the atmosphere to reach our eyes, and much of the blue light has been deflected and scattered, leaving mostly red and yellow light.