The sky appears blue during the day due to a phenomenon called Rayleigh scattering. Sunlight, which contains all colors of the visible spectrum, interacts with nitrogen and oxygen molecules in Earth's atmosphere. These molecules scatter shorter-wavelength blue light more effectively than longer- wavelength colors like red or yellow, dispersing blue light across the sky in all directions.

Scattering Process

Blue light waves are shorter (around 450-495 nanometers) and thus collide more frequently with air molecules, causing them to bounce in every direction rather than traveling straight through. This scattered blue light reaches our eyes from overhead, making the sky look vividly blue on clear days. Red light, with longer wavelengths, passes through more easily, which is why sunsets appear reddish when the sun's path through the thicker atmosphere scatters away the blues.

Variations

Dust, pollution, or water droplets can alter this effect, sometimes muting the blue or adding hues like gray. At higher altitudes or in space, the sky appears black because there's no atmosphere to scatter light. Our eyes are also more sensitive to blue than violet, enhancing the perception despite violet scattering more.