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Spectrum of blue sky clearly showing solar Fraunhofer lines and atmospheric water absorption band.

Diffuse sky radiation is solar radiation reaching the Earth's surface after having been scattered from the direct solar beam by molecules or suspensoids in the atmosphere. It is also called skylight, diffuse skylight, or sky radiation and is the reason for changes in the colour of the sky. Of the total light removed from the direct solar beam by scattering in the atmosphere (approximately 25 percent of the incident radiation when the sun is high in the sky, depending on the amount of dust and haze in the atmosphere), about two-thirds ultimately reaches the earth as diffuse sky radiation. Image File history File links Question_book-3. ... Image File history File links Download high-resolution version (2501x1596, 70 KB) Spectrum of blue sky somewhat near the horizon pointing east at around 3 or 4 pm on a clear day. ... Image File history File links Download high-resolution version (2501x1596, 70 KB) Spectrum of blue sky somewhat near the horizon pointing east at around 3 or 4 pm on a clear day. ... This article is about the colour. ... Solar Fraunhofer lines In physics and optics, the Fraunhofer lines are a set of spectral lines named for the German physicist Joseph von Fraunhofer (1787--1826). ... Solar irradiance spectrum at top of atmosphere. ... This article is about Earth as a planet. ... Scattering is a general physical process whereby some forms of radiation, such as light, sound or moving particles, for example, are forced to deviate from a straight trajectory by one or more localized non-uniformities in the medium through which it passes. ... 3D (left and center) and 2D (right) representations of the terpenoid molecule atisane. ... A suspensolid, as defined in Stedmans Medical Dictionary, is A colloid solution in which the disperse particles are solid and remain sharply demarcated from the fluid in which they are suspended. ... Air redirects here. ... For other uses, see Light (disambiguation). ... For other uses, see Sky (disambiguation). ...

The important processes in the atmosphere (Rayleigh scattering and Mie scattering) are elastic. No energy transformation results, only a change in the spatial distribution of the radiation. Rayleigh scattering causing the blue hue of the sky and the reddening at sunset Rayleigh scattering (named after Lord Rayleigh) is the scattering of light, or other electromagnetic radiation, by particles much smaller than the wavelength of the light. ... Mie theory, also called Lorenz-Mie theory or Lorenz-Mie-Debye theory, is a complete analytical solution of Maxwells equations for the scattering of electromagnetic radiation by spherical particles (also called Mie scattering). ... In scattering theory and in particular in particle physics, elastic scattering is one of the specific forms of scattering. ...

Colour

Clear blue sky.

red sky at sunrise

Comparison of the scattering efficiency of blue light in the atmosphere compared to red light.

Overcast sky.

The sunlit sky appears 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.^[1] 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. Image File history File links Download high resolution version (1003x670, 302 KB)From: http://firepix. ... Image File history File links Download high resolution version (1003x670, 302 KB)From: http://firepix. ... Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... Image File history File linksMetadata Size of this preview: 800 × 600 pixel Image in higher resolution (1280 × 960 pixel, file size: 441 KB, MIME type: image/jpeg) Photo by Derek Morrison, 10/15/04. ... Image File history File linksMetadata Size of this preview: 800 × 600 pixel Image in higher resolution (1280 × 960 pixel, file size: 441 KB, MIME type: image/jpeg) Photo by Derek Morrison, 10/15/04. ... Look up air in Wiktionary, the free dictionary. ... For other uses, see Wavelength (disambiguation). ... A typical sunrise, in New Zealand A sunrise through clouds over Oakland, California. ... A composite image showing the terminator dividing night from day, running across Europe and Africa. ...

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. Rayleigh scattering causing the blue hue of the sky and the reddening at sunset Rayleigh scattering (named after Lord Rayleigh) is the scattering of light, or other electromagnetic radiation, by particles much smaller than the wavelength of the light. ... Mie theory, also called Lorenz-Mie theory or Lorenz-Mie-Debye theory, is a complete analytical solution of Maxwells equations for the scattering of electromagnetic radiation by spherical particles (also called Mie scattering). ... See also list of optical topics. ...

Neutral points

There are three commonly detectable points of zero polarization of diffuse sky radiation (known as neutral points) lying along the vertical circle through the sun. In electrodynamics, polarization (also spelled polarisation) is the property of electromagnetic waves, such as light, that describes the direction of their transverse electric field. ... In astronomy, a vertical circle is a great circle on the celestial sphere that is perpendicular to the horizon. ... Sol redirects here. ...

• The Arago point, named after its discoverer, is customarily located at about 20° above the antisolar point; but it lies at higher altitudes in turbid air. The latter property makes the Arago distance a useful measure of atmospheric turbidity.

• The Babinet point, discovered by Babinet in 1840, is located about 15° to 20° above the sun, hence it is difficult to observe because of solar glare.

• The Brewster point, discovered by Brewster in 1840, is located about 15° to 20° below the sun; hence it is difficult to observe because of solar glare.

The antisolar point is the imaginary point on the celestial sphere exactly opposite the sun. ... Turbidity standards of 5, 50, and 500 NTU Turbidity is a cloudiness or haziness of a fluid, or of air, caused by individual particles (suspended solids) that are generally invisible to the naked eye, similar to smoke in air. ...

Under an overcast sky

There is essentially no direct sunlight under an overcast sky, so all light is then diffuse sky radiation. The flux of light is not very wavelength dependent because the cloud droplets are larger than the light's wavelength and scatter all colours approximately equally. The light passes through the translucent clouds in a manner similar to frosted glass. The intensity ranges (roughly) from 1/6 of direct sunlight for relatively thin clouds down to 1/1000 of direct sunlight under the extreme of thickest storm clouds.

See also

• Aerial perspective
• Daylight
• Nighttime airglow
• Tyndall effect

This article needs cleanup. ... Look up daylight in Wiktionary, the free dictionary. ... The airglow is the very weak emission of visible light by the earths atmosphere, which means that the night sky is never completely dark. ... Shot of sunbeams breaking through nebula bank The term Tyndall effect is usually applied to the effect of light scattering on particles in colloid systems, such as suspensions or emulsions. ...

References

1. ^ "Rayleigh scattering." Encyclopædia Britannica. 2007. Encyclopædia Britannica Online. 16 Nov. 2007.

External links

• Why is the sky blue?
• Why is the sky blue?
• Why is the sky blue? Science made simple
• Blue Sky and Rayleigh Scattering

Books

• Pesic, Peter (2005). Sky in a Bottle. The MIT Press. ISBN 978-0-262-16234-0.