Color
The sunlit sky is blue because air scatters short-wavelength light more than longer wavelengths. Since blue light is at the short wavelength end of the visible spectrum, it is more strongly scattered in the atmosphere than long wavelength red light. The result is that the human eye perceives blue when looking toward parts of the sky other than the sun. The color perceived is similar to that obtained by a monochromatic blue of wavelength 474–476 nm mixed with white light, i.e., an unsaturated blue light.
Near sunrise and sunset, most of the light we see comes in nearly tangent to the Earth's surface, so that the light's path through the atmosphere is so long that much of the blue and even green light is scattered out, leaving the sun rays and the clouds it illuminates red. Therefore, when looking at the sunset and sunrise, you will see the color red more than any of the other colors.
Scattering and absorption are major causes of the attenuation of radiation by the atmosphere. Scattering varies as a function of the ratio of the particle diameter to the wavelength of the radiation. When this ratio is less than about one-tenth, Rayleigh scattering occurs in which the scattering coefficient varies inversely as the fourth power of the wavelength. At larger values of the ratio of particle diameter to wavelength, the scattering varies in a complex fashion described, for spherical particles, by the Mie theory; at a ratio of the order of 10, the laws of geometric optics begin to apply.
Read more about this topic: Diffuse Sky Radiation
Famous quotes containing the word color:
“Surely the day will come when color means nothing more than skin tone, when religion is seen uniquely as a way to speak one’s soul; when birth places have the weight of a throw of the dice and all men are born free, when understanding breeds love and brotherhood.”
—Josephine Baker (1906–1975)
“When a bachelor of philosophy from the Antilles refuses to apply for certification as a teacher on the grounds of his color I say that philosophy has never saved anyone. When someone else strives and strains to prove to me that black men are as intelligent as white men I say that intelligence has never saved anyone: and that is true, for, if philosophy and intelligence are invoked to proclaim the equality of men, they have also been employed to justify the extermination of men.”
—Frantz Fanon (1925–1961)