Why is the sky blue?

The sky appears blue because of a phenomenon called Rayleigh scattering. When sunlight enters Earth’s atmosphere, molecules and small particles scatter shorter wavelengths of light, such as blue and violet, more than longer wavelengths like red. Our eyes are more sensitive to blue light and less to violet, so we perceive the sky as blue. This effect is most pronounced when the Sun is high in the sky. During sunrise or sunset, the sky may appear red or orange because the sunlight travels through more atmosphere, scattering shorter wavelengths and allowing longer wavelengths to dominate.