Bond albedo

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Bond albedo

The Bond albedo is the fraction of power in the total electromagnetic radiation incident on an astronomical body that is scattered back out into space. It takes into account all wavelengths at all phase angles

Phase angle (astronomy)

Phase angle in Observational astronomys is the angle between the light incident onto an observed object and the light reflected from the object....
.

It is an important quantity for characterising a planetary body's energy balance.

For objects in the solar system, the relevant weighting of each wavelength is proportional to the solar power spectrum.

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Encyclopedia

Phase angle (astronomy)

Albedo

The albedo of an object is the extent to which it diffusely reflects light from the Sun. It is therefore a more specific form of the term reflectivity....
s the Bond albedo is a value between 0 and 1.

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.

The Bond albedo is named for the American astronomer George Phillips Bond

George Phillips Bond

George Phillips Bond was an United States 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 Cranch Bond Jr....
(1825-1865), who originally proposed it. It was originally defined for spherical bodies, but is also applicable for irregular objects.

Phase integral

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

Geometric albedo

The geometric albedo of an astronomical body is the ratio of its actual brightness at zero Phase angle to that of an idealized flat, fully reflecting, diffuse reflection disk with the same cross-section....
(p) by the expression

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

The phase angle

Angle

In geometry and trigonometry, an angle is the figure formed by two Ray sharing a common endpoint, called the vertex of the angle . The magnitude of the angle is the "amount of rotation" that separates the two rays, and can be measured by considering the length of circular arc swept out when one ray is rotated about the vertex to coincide...
a 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, a is very small, while backlit objects or the new moon have a close to 180°.

Examples

The Bond albedo may be greater or smaller than the geometric albedo, depending on surface and atmospheric properties of the body in question. Some examples :

Name	Bond Albedo	Geometric albedo
Mercury Mercury (planet) Mercury is the innermost and smallest planet in the Solar System, orbiting the Sun once every 88 days. The orbit of Mercury has the highest Orbital eccentricity of all the Solar System planets, and it has the smallest axial tilt....	0.119	0.138
Venus Venus Venus is the second-closest planet to the Sun, orbiting it every 224.7 Earth days. The planet is named after Venus , the Roman mythology goddess of love....	0.75	0.84
Earth Earth Earth is the third planet from the Sun. Earth is the largest of the terrestrial planets in the Solar System in diameter, mass and density. It is also referred to as the World and Wiktionary:Terra.Note that by International Astronomical Union convention, the term "Terra" is used for naming extensive land masses, rather...	0.29	0.367
Moon Moon The Moon is Earth's only natural satellite and the List of natural satellites by diameter satellite in the Solar System. The average centre-to-centre distance from the Earth to the Moon is km, about thirty times the diameter of the Earth....	0.123	0.113
Mars MARS In cryptography, MARS is a block cipher that was IBM's submission to the Advanced Encryption Standard process. MARS was selected as an AES finalist in August 1999, after the AES2 conference in March 1999, where it was voted as the fifth and last finalist algorithm....	0.16	0.15
Enceladus Enceladus (moon) 'Enceladus' , is the sixth-largest Moons of Saturn of Saturn . It was discovered in 1789 by William Herschel. Until the two Voyager program spacecraft passed near it in the early 1980s, very little was known about this small moon besides the identification of water ice on its surface....	0.99	1.4
Pluto Pluto Pluto , Minor planet names Pluto, is the second-largest known dwarf planet in the Solar System and the tenth-largest body observed directly orbiting the Sun....	0.4	0.44-0.61

Bond albedo

Phase integral

Examples

See also

External links