The sky appears blue because of a phenomenon called Rayleigh scattering. Here’s how it works: Sunlight is white light, which is a combination of all colors (wavelengths) of visible light. As sunlight enters Earth’s atmosphere, it collides with molecules and tiny particles in the air. Shorter wavelengths (blue and violet) scatter more strongly than longer wavelengths (like red and orange). Although violet scatters even more than blue, our eyes are more sensitive to blue light, and some violet is absorbed by the upper atmosphere. As a result, we perceive the sky as blue during the day. At sunrise and sunset, the sun’s light passes through more atmosphere, scattering the blue light away and letting the reds and oranges dominate—hence those beautiful colors during those times.