The direct (albedo) effect is generally to cool the planet; the indirect effect (the particles act as cloud condensation nuclei and thereby change cloud properties) is less certain
the effects are:
 Aerosol direct effect
Aerosols directly scatter and absorb radiation
The scattering of radiation causes atmospheric cooling, whereas absorption can cause atmospheric warming
Aerosols modify the properties of clouds through a subset of the aerosol population called cloud condensation nuclei
In extremely polluted cities like Delhi, aerosol pollutants influence local weather and induce an urban cool island effect during the day
Black carbon
Another albedo-related effect on the climate is from black carbon particles
Black carbon is a bigger cause of the melting of the polar ice cap in the Arctic than carbon dioxide due to its effect on the albedo
Astronomical albedo 
In astronomy, the term albedo can be defined in several different ways, depending upon the application and the wavelength of electromagnetic radiation involved
Optical or visual albedo
The albedos of planets, satellites and minor planets such as asteroids can be used to infer much about their properties
The study of albedos, their dependence on wavelength, lighting angle ("phase angle"), and variation in time composes a major part of the astronomical field of photometry
For small and far objects that cannot be resolved by telescopes, much of what we know comes from the study of their albedos
Enceladus, a moon of Saturn, has one of the highest known optical albedos of any body in the Solar System, with an albedo of 0.99
Another notable high-albedo body is Eris, with an albedo of 0.96
Many small objects in the outer Solar System and asteroid belt have low albedos down to about 0.05
A typical comet nucleus has an albedo of 0.04
Such a dark surface is thought to be indicative of a primitive and heavily space weathered surface containing some organic compounds
The overall albedo of the Moon is measured to be around 0.14, but it is strongly directional and non-Lambertian, displaying also a strong opposition effect
Although such reflectance properties are different from those of any terrestrial terrains, they are typical of the regolith surfaces of airless Solar System bodies
Their values can differ significantly, which is a common source of confusion
One of these five parameters is yet another type of albedo called the single-scattering albedo
It is used to define scattering of electromagnetic waves on small particles
It depends on properties of the material (refractive index), the size of the particle, and the wavelength of the incoming radiation
Radar albedo
In planetary radar astronomy, a microwave (or radar) pulse is transmitted toward a planetary target (e.g
Moon, asteroid, etc.) and the echo from the target is measured
In most instances, the transmitted pulse is circularly polarized and the received pulse is measured in the same sense of polarization as the transmitted pulse (SC) and the opposite sense (OC)
If the surface is rough at the wavelength scale or there is significant penetration into the regolith, there will be a significant SC component in the echo caused by multiple scattering
A smooth metallic sphere would have
Radar albedos of Solar System objects

The values reported for the Moon, Mercury, Mars, Venus, and Comet P/2005 JQ5 are derived from the total (OC+SC) radar albedo reported in those references
History 
The term albedo was introduced into optics by Johann Heinrich Lambert in his 1760 work Photometria
Its name in English is a (pronounced ), plural aes
It is similar in shape to the Ancient Greek letter Alpha, from which it derives
The uppercase version consists of the two slanting sides of a triangle, crossed in the middle by a horizontal bar
The lowercase version can be written in two forms: the double-storey a and single-storey ɑ
The latter is commonly used in handwriting and fonts based on it, especially fonts intended to be read by children, and is also found in italic type
In English grammar, "a", and its variant "an", are indefinite articles
In turn, the ancestor of aleph may have been a pictogram of an ox head in proto-Sinaitic script influenced by Egyptian hieroglyphs, styled as a triangular head with two horns extended
The Etruscans brought the Greek alphabet to their civilization in the Italian Peninsula and left the letter unchanged
Typographic variants 

During Roman times, there were many variant forms of the letter "A"
First was the monumental or lapidary style, which was used when inscribing on stone or other "permanent" media
There was also a cursive style used for everyday or utilitarian writing, which was done on more perishable surfaces
Variants also existed that were intermediate between the monumental and cursive styles
The known variants include the early semi-uncial, the uncial, and the later semi-uncial
At the end of the Roman Empire (5th century AD), several variants of the cursive minuscule developed through Western Europe
By the ninth century, the Caroline script, which was very similar to the present-day form, was the principal form used in book-making, before the advent of the printing press
This form was derived through a combining of prior forms
15th-century Italy saw the formation of the two main variants that are known today
These variants, the Italic and Roman forms, were derived from the Caroline Script version
The Italic form, also called script a, is used in most current handwriting; it consists of a circle and vertical stroke on the right ("ɑ")
This slowly developed from the fifth-century form resembling the Greek letter tau in the hands of medieval Irish and English writers