Why Does the Sunset Change Colors?

Light, the Light Spectrum, and Our Atmosphere

Humans have always wondered about their environment, especially the sky. Every day, our sky goes from solid blue to a smorgasbord of reds, oranges, yellows, pinks, and who knows what other colors during sunset. As we shall see, the reason that the sky is blue during the day and the reason that the sky isn't blue during sunrise and sunset are both linked. It all has to do with the scattering of light into its specific colors of the rainbow by atmospheric particles.

Blue Skys, Vivid Sunsets

Visible light is composed of all colors in the visible light spectrum, and the breakup of white light into its respective colors can be viewed through a prism--breaking the white light into the familiar rainbow colors of red, orange, yellow, green, blue, indigo and violet.his listing is from longest wavelength to the shortest wavelength. During the day, the shorter-wavelength blues and violets are scattered by molecules and other particles in the air. This scattered light reaches our eyes from all directions on a clear day in the afternoon, and we view the sky as blue. Longer wavelength visible light, like reds and oranges, is not affected by the relatively few scatterings of a few chance molecules.

Sunset and Sunrise: More Atmosphere, More Scattering

During sunrise and sunset, because of the angle of the sun's rays, sunlight must pass through much more of our atmosphere before reaching our eyes. This means that the sunlight has the chance to be scattered more completely, coming into contact with even more molecules and particles in the air. This makes the scattering effect become even more pronounced, and these molecules scatter away all of the blue and violet light. The longer wavelengths of red and orange light are not affected by the long path through the atmosphere, and are still detected by our eyes. This is the reason that the sunsets and sunrises can look red, orange, yellow or even pink.

References

• ScienceDaily.com: What Determines Sky's Colors at Sunrise and Sunset?
• Physics.UCSD.Edu: Dynamic Light Scattering
• Spaceplace.NASA.gov: Why is the Sky Blue?