Chippewa Valley Times

This article is part of the "Curious Kids" series, where academic experts answer children's questions. It originated from The Conversation, an independent and nonprofit source of news and commentary.

Mariana A-E., an 11-year-old from Tucson, Arizona, asked why the sky is blue. The explanation involves science, specifically physics and chemistry. According to experts, colors we see are produced in different ways, some explained by physics and others by chemistry.

The sky appears blue because sunlight travels through the atmosphere filled with nitrogen and oxygen molecules. These molecules are tiny, about 0.4 nanometers each. When sunlight encounters these molecules, the light is scattered. Blue light scatters more than other colors due to its shorter wavelength.

John William Strutt, known as Lord Rayleigh, explained this phenomenon around 1870. His discovery led to the term "Rayleigh scattering," describing how blue light from the Sun scatters most when passing through Earth's atmosphere.

Other atmospheric gases like carbon dioxide or methane have minimal impact on sky color but can affect global climate.

Without scattering, the sky would appear dark like on the Moon, which lacks an atmosphere. A rainbow shows all sunlight components broken into visible spectrum colors: red, orange, yellow, green, blue, indigo and violet (ROY G. BIV). Blue light scatters more efficiently than other colors.

At sunrise and sunset when the Sun is near the horizon, its light passes through more atmosphere layers. Blue and green lights scatter so well that they become less visible; instead red and orange hues dominate due to longer wavelengths traveling directly to observers' eyes.

Understanding color science has been significant for humans throughout history in various aspects including art expression or daily life choices like clothing selection.