When sunlight passes through the atmosphere, the fine particles in the air scatter the blue color (shorter wavelengths) more strongly than red. The scattered blue light enters our eyes. Within the visible range of light, red light waves are scattered the least by atmospheric gas molecules. So at sunrise and sunset, when the sunlight travels a long path through the atmosphere to reach our eyes, the blue light has been mostly removed, leaving mostly red and yellow light remaining.Blue light is scattered more than the other colors because it travels as shorter, smaller waves. This is why we see a blue sky most of the time.