albedo


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albedo

(ălbē`dō), reflectivity of the surface of a planet, moon, asteroid, or other celestial body that does not shine by its own light. Albedo is measured as the fraction of incident light that the surface reflects back in all directions. A perfect reflector by definition has an albedo of unity, i.e., all the incident light is reflected; a body that reflects no light at all would have an albedo of zero. Real surfaces have albedos between these values. The albedos of planets, moons, and asteroids provide valuable information about the structure and composition of their surfaces. The dark regions on the earth's moon give it the very low average albedo of 0.07, while highly reflective clouds give Venus an albedo of 0.85, the highest of any body in the solar system.

albedo

(al-bee -doh) The reflecting power of a nonluminous object, such as a planet or planetary surface feature. In general, it is the ratio of the total amount of light reflected in all directions to the amount of incident light: an albedo of 1.0 indicates a perfectly reflecting surface whereas a value of 0.0 indicates a totally black surface that absorbs all incident light.

Albedo can be expressed in several ways. The Bond albedo is the fraction of the total incident energy that a body reflects in all directions. It is calculated over all wavelengths and its value therefore depends on the spectrum of the incident radiation. This parameter determines the energy balance of a body such as a planet. The geometrical albedo is the ratio of the light reflected in the backscattering direction (zero phase angle or opposition) by an object, to that which would be reflected by a perfectly diffusing disk of the same size. The wavelength or range of wavelengths at which the geometrical albedo applies must be defined. Geometrical albedo is commonly used for Solar System objects. The hemispherical albedo is the reflecting power of a nonluminous body such as a planet, assuming the body is a sphere with a diffuse surface reflecting incoming parallel light rays in all directions. The phase integral is the ratio of the Bond albedo to the geometrical albedo averaged over the incident spectrum. See also Table 1, backmatter.

Albedo

Percentage of light reflected off a surface; a material with a high albedo is very reflective.

Albedo

(religion, spiritualism, and occult)

Albedo (literally, “whiteness”) is a measure of the power of a planet, moon, or asteroid to reflect light.

Albedo

 

a characteristic of the reflecting properties of the surface of a body: the ratio of the flow of radiation scattered by a surface to the flow falling on that surface. There is true albedo (or diffuse albedo, Lambert albedo, the coefficient of diffuse reflection) and apparent albedo (or the brightness factor). True albedo is the ratio of the flow scattered in all directions by a plane element of a surface to the flow falling on that element. Apparent albedo is the ratio of the brightness of a surface illuminated by parallel bundles of rays to the brightness of an absolutely white surface (that is, a surface for which the ratio of the brightness to the illumination does not depend on the direction and for which the true albedo equals one) perpendicular to the illuminated beam.

In astronomy the concept of albedo is generalized and is considered as a characteristic of a non-self-luminous heavenly body as a whole. Spherical albedo (Bond’s albedo) is the ratio of light flow scattered by a body in all directions to the flow falling on the body. Geometric albedo is the ratio of the mean brightness of an object given a phase angle of zero to the brightness of an absolutely white plane screen perpendicular to the sun’s rays, placed in the same point and visible under the same solid angle as the object. Illustrative albedo differs from geometric albedo in that the mean brightness of an absolutely white sphere is the standard, rather than the brightness, of a planar screen.

Integral (energetic) albedo is also considered, for a whole flow of radiation, as are monochromatic albedo (in monochromatic light) and albedo in various regions of the spectrum, such as ultraviolet, visual, and infrared. The true visual albedo of the earth’s surface varies from 0.03 ( a water surface) to 0.9 (fresh snow, clouds). The albedo of vegetation in the visible range of the spectrum is 0.1–0.3 and reaches 0.9 in the infrared range. The spherical visual albedo of the earth, determined according to the earthlight on the moon, based on measurements with artificial cosmic bodies and also according to the calculation of the heat balance of the earth, is close to 0.45. The albedo of the planets and satellites lacking an atmosphere (Mercury, the moon) is usually low and close to 0.07; the albedo of planets with a dense cloud atmosphere (Venus, Jupiter, Saturn, Uranus) is close to 0.6; the albedo of Mars is approximately 0.15.

REFERENCE

Sharonov, V. V. Priroda planet. Moscow, 1958.

G. A. LEIKIN

albedo

[al′bē‚dō]
(nucleonics)
The reflection factor a surface, such as paraffin, has for neutrons.
(optics)
That fraction of the total light incident on a reflecting surface, especially a celestial body, which is reflected back in all directions.

albedo

The proportion of incident light reflected, as by a planet. In meteorology, it is the property of the earth to radiate back some solar radiation to the atmosphere. It is the ratio of the amount of electromagnetic or solar radiation reflected by a body to the amount incident upon it, often expressed as a percentage. The albedo of the earth is 34%.
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