The Bond albedo (or ''spheric albedo'' or ''planetary albedo'' or ''bolometric albedo''), named after the American astronomer

George Phillips Bond George Phillips Bond (May 20, 1825February 17, 1865) was an American astronomer. He was the son of William Cranch Bond. Some sources give his year of birth as 1826. His early interest was in nature and birds, but after his elder brother William ...

(1825–1865), who originally proposed it, is the fraction of

power Power most often refers to: * Power (physics), meaning "rate of doing work" ** Engine power, the power put out by an engine ** Electric power * Power (social and political), the ability to influence people or events ** Abusive power Power may a ...

in the total

electromagnetic radiation In physics, electromagnetic radiation (EMR) consists of waves of the electromagnetic field, electromagnetic (EM) field, which propagate through space and carry momentum and electromagnetic radiant energy. It includes radio waves, microwaves, inf ...

incident on an astronomical body that is scattered back out into space. Because the Bond albedo accounts for all of the light scattered from a body at all

wavelength In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats. It is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, tro ...

s and all phase angles, it is a necessary quantity for determining how much energy a body absorbs. This, in turn, is crucial for determining the

equilibrium temperature The planetary equilibrium temperature is a theoretical temperature that a planet would be if it were a black body being heated only by its parent star. In this model, the presence or absence of an atmosphere (and therefore any greenhouse effect) is ...

of a body. Because bodies in the outer Solar System are always observed at very low phase angles from the Earth, the only reliable data for measuring their Bond albedo comes from spacecraft.

Phase integral

The Bond albedo (''A'') is related to the

geometric albedo In astronomy, the geometric albedo of a celestial body is the ratio of its actual brightness as seen from the light source (i.e. at zero phase angle) to that of an ''idealized'' flat, fully reflecting, diffusively scattering ( Lambertian) disk w ...

(''p'') by the expression :

A = pq

where ''q'' is termed the ''phase integral'' and is given in terms of the directional scattered flux ''I''(''α'') into phase angle ''α'' (averaged over all wavelengths and azimuthal angles) as :

q = 2\int_0^\pi \frac \sin\alpha \, d\alpha.

The phase

angle In Euclidean geometry, an angle is the figure formed by two Ray (geometry), rays, called the ''Side (plane geometry), sides'' of the angle, sharing a common endpoint, called the ''vertex (geometry), vertex'' of the angle. Angles formed by two ...

''α'' is the angle between the source of the radiation (usually the Sun) and the observing direction, and varies from zero for light scattered back towards the source, to 180° for observations looking towards the source. For example, during opposition or looking at the full moon, α is very small, while backlit objects or the new moon have α close to 180°.

Examples

The Bond albedo is a value strictly between 0 and 1, as it includes all possible scattered light (but not radiation from the body itself). This is in contrast to other definitions of

albedo Albedo (; ) is the measure of the diffuse reflection of sunlight, solar radiation out of the total solar radiation and measured on a scale from 0, corresponding to a black body that absorbs all incident radiation, to 1, corresponding to a body ...

such as the geometric albedo, which can be above 1. In general, though, the Bond albedo may be greater or smaller than the geometric albedo, depending on the surface and atmospheric properties of the body in question. Some examples:Albedo of the Earth
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References

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External links

discussion of Lunar albedo
Electromagnetic radiation Astrophysics Radiometry Scattering, absorption and radiative transfer (optics)

Phase integral

Examples

See also

References

External links