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Why does the Sun often appear red or orange near sunrise and sunset?

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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.

The Sun appears red or orange near sunrise and sunset primarily due to a phenomenon known as Rayleigh scattering.

Sunlight is composed of all the colors of the visible spectrum, each with a different wavelength. Shorter wavelengths, such as blue and violet, are scattered much more strongly by atmospheric gas molecules than longer wavelengths, such as red and orange.123

When the Sun is near the horizon at sunrise or sunset, its rays must travel through a much thicker layer of the atmosphere to reach an observer than they do when the Sun is high overhead. During this extended passage, the shorter-wavelength blue and violet light is scattered out of the direct beam of sunlight by air molecules and particles. Consequently, the light that reaches the observer's eyes is dominated by the longer-wavelength red and orange components, which are less affected by scattering.2431