Understanding the Color of the Sky

The sky's color results from light scattering. Sunlight, a white light mix, hits atmospheric molecules, scattering blue light more than other colors due to its shorter wavelength.

Rayleigh scattering occurs when light travels through Earth's atmosphere. This scattering favors shorter wavelengths, the blues, over longer wavelengths, the reds, making the sky appear blue.

During sunrise and sunset, the sky turns red or orange. This is because the light path through the atmosphere is longer, scattering short wavelengths and leaving behind the longer red wavelengths.

Not widely known, but the presence of oxygen in Earth's atmosphere is partly why the sky is blue. Oxygen molecules are particularly good at scattering the blue light.

Other planets have different sky colors. Mars, for instance, has a reddish sky due to its dust-filled atmosphere, which scatters sunlight differently than Earth's atmosphere.

Atmospheric pollution affects sky color by scattering different light wavelengths. This can cause hazier, whiter skies, reducing the scattering of blue light.

Humans are more sensitive to blue light. Our eyes have evolved under the blue sky, which might explain our sensitivity and why clear blue skies are generally perceived as clear weather.

The moon has no atmosphere, so its sky is always black, even during the lunar day when the sun shines brightly.