Jellby nous apporta ses lumieres ainsi en ce 2004/04/24 09:47... :

>Among other things, Alain tuvo wrote:
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>>Albedo is linear. A planet with an albedo of 0.50 reflect 50% (2/4) of
>>the incident lignt, albedo 0.25 mean 25% (1/4) of incident light, albedo
>>0.75 = 3/4.
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>But it's not necessarily constant, is it?
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>A planet's albedo could be 0.25 with a certain amount of incident light, but 
>maybe, with twice as much incident light, its albedo would be only 0.21 
>(not talking about changes in the planet's surface, angle of incidence, 
>etc.)
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Albedo is the fraction of the total light, from low infrared to the 
hardest UVs, faling onto a celestial body that is sent back into space. 
Depending on the caracteristics of the surface, the body can be more 
reflective along prevelieged directions, but the amount of incident 
light won't chage it. Taking the moon closer to the sun, like at the 
same distance as Mercury, will have no effect on it's albedo, altough it 
will looks much brighter if you are to look at it from the same distance 
as you look at it now.
The albedo depend entirely and only on the nature of the surface. Take 
Venus and bring it on earth orbit, then most of it's clouds will rain 
down, giving a lower albedo. Bring it down to Mercury orbit and it's 
clouds will completely vaporize, maybe escaping into space, also 
lowering it's albedo.
 From my past time in amateur astronomy, my physics cources and tons of 
reading on the subject...

Alain

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