Sunsets often look red because sunlight travels through more air, which scatters away the blue light.

The longer version

Near the horizon, sunlight slants through a much longer slab of air than at midday. Over that extended path, scattering removes most of the blue and green, so only the longest wavelengths survive the trip and arrive at the eye as orange and red, with the reddest tones appearing when the sun is lowest.

Dust, smoke, and volcanic ash enhance the effect, which is why sunsets after large eruptions can be spectacular for months. The same geometry reddens the sun's disc itself, flattening it slightly near the horizon because lower light is bent more. Sunrises follow the identical rule.

Where this entry sits

These facts explore how light behaves and how human eyes turn it into the colors we see. Along the way you meet rainbows, prisms, mirrors, shadows, lasers, and optical tricks that fool our vision every day. The full list sits on the Color and Light page, where every entry is listed in order.

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More From Color and Light

Eight more entries

Laser light differs from ordinary light because its waves are aligned and share a single wavelength.

The traditional spectrum is often listed as seven colors, including red, orange, yellow, green, blue, indigo, and violet.

Most people cannot distinguish indigo from blue or violet in an ordinary rainbow.

Color blindness most often involves difficulty telling red from green rather than seeing no color at all.

Some animals, including many birds, see ultraviolet light that human eyes cannot detect.

Mixing red, green, and blue light in equal amounts produces white light on a screen.

Mixing yellow and blue paint produces green, which surprises people taught that mixing light works differently.

Pigments create color by subtracting wavelengths, while lights create color by adding wavelengths together.

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