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Why does Rayleigh scattering make the daytime sky look blue?

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Diagram of a tree leaf illustrating photosynthesis, with arrows showing sunlight, water, and carbon dioxide entering the leaf and sugars and oxygen being produced. A person is shown beside the tree to demonstrate the exchange of oxygen and carbon dioxide between plants and animals. — electromagnetic radiation Diagram of photosynthesis showing how water, light, and carbon dioxide are absorbed by a plant to produce oxygen, sugars, and more carbon dioxide.

Rayleigh scattering is the process by which electromagnetic radiation is dispersed by particles significantly smaller than the radiation's wavelength, such as gas molecules in Earth's atmosphere.1

When sunlight enters the atmosphere, it interacts with nitrogen and oxygen molecules. These molecules scatter the light in various directions. According to Rayleigh's law, the intensity of this scattered light is inversely proportional to the fourth power of its wavelength. Consequently, shorter wavelengths—specifically blue light—are scattered much more strongly than longer wavelengths like red or yellow.12

As we look away from the Sun, our eyes perceive this scattered blue light coming from all parts of the sky. While violet light has an even shorter wavelength and is also scattered, the sky appears blue rather than violet because human eyes are significantly more sensitive to blue light.13