As a ray of white sunlight travels through the atmosphere to an observer, some of the colors are scattered out of the beam by air molecules andairborne particles, changing the final color of the beam the viewer sees.Because the shorterwavelength components, such as blue and green, scatter more strongly, these colors are preferentially removed from the beam.^[2] At sunrise and sunset, when the path through the atmosphere is longer, the blue and green components are removed almost completely, leaving the longer wavelength orange and redhues we see at those times. The remaining reddened sunlight can then be scattered by cloud droplets and other relatively large particles to light up the horizon red and orange.^[3] The removal of the shorter wavelengths of light is due toRayleigh scattering by air molecules and particles much smaller than the wavelength of visible light (less than 50 nm in diameter).^[4][5] The scattering by cloud droplets and other particles with diameters comparable to or larger than the sunlight's wavelengths (> 600 nm) is due toMie scattering and is not strongly wavelength-dependent. Mie scattering is responsible for the light scattered by clouds, and also for the daytime halo of white light around the Sun (forward scattering of white light).^[6][7][8]

Sunset colors are typically more brilliant than sunrise colors, because the evening air contains more particles than morning air.^[2][3][5][8] Sometimes just before sunrise or after sunset agreen flash can be seen.^[9]

Ash from volcanic eruptions, trapped within thetroposphere, tends to mute sunset and sunrise colors, while volcanic ejecta that is instead lofted into thestratosphere (as thin clouds of tiny sulfuric acid droplets), can yield beautiful post-sunset colors calledafterglows and pre-sunrise glows. A number of eruptions, including those ofMount Pinatubo in 1991 andKrakatoa in 1883, have produced sufficiently highstratus clouds containingsulfuric acid to yield remarkable sunset afterglows (and pre-sunrise glows) around the world. The high-altitude clouds serve to reflect strongly reddened sunlight still striking the stratosphere after sunset, down to the surface.

1. ^Maerz and PaulA Dictionary of Color New York:1930 McGraw-Hill Page 205; Color Sample of Sunset: Page 43 Plate 10 Color Sample C4
2. ^^abK. Saha (2008).The Earth's Atmosphere – Its Physics and Dynamics. Springer. p. 107.ISBN 978-3-540-78426-5.
3. ^^abB. Guenther, ed. (2005).Encyclopedia of Modern Optics. Vol. 1.Elsevier. p. 186.
4. ^"Hyperphysics, Georgia State University". Hyperphysics.phy-astr.gsu.edu. Retrieved2012-04-07.
5. ^^abCraig Bohren (ed.),Selected Papers on Scattering in the Atmosphere, SPIE Optical Engineering Press, Bellingham, WA, 1989
6. ^Corfidi, Stephen F. (October 2024)."The Science of Sunsets". Norman, OK: NOAA/NWS Storm Prediction Center.
7. ^"Atmospheric Aerosols: What Are They, and Why Are They So Important?". nasa.gov. August 1996.
8. ^^abE. Hecht (2002).Optics (4th ed.). Addison Wesley. p. 88.ISBN 0-321-18878-0.
9. ^"Red Sunset, Green Flash".
10. ^Maerz and PaulA Dictionary of Color New York:1930 McGraw-Hill Page 205
11. ^Maerz and PaulA Dictionary of Color New York:1930 McGraw-Hill Page 205; Color Sample of Sunset: Page 43 Plate 10 Color Sample J6