On a clear day, the sky appears blue because molecules in the Earth's atmosphere scatter sunlight in all directions. Blue light is scattered more than other colors because it travels in shorter, smaller waves, which is why we see a blue sky most of the time. This phenomenon is known as Rayleigh scattering. The Earth's atmosphere is composed of various gases, but nitrogen and oxygen are the primary ones that scatter sunlight. At sunrise and sunset, the sky can appear red or orange because the sun's light passes through more of the atmosphere, reducing the shorter wavelengths.
