Alain wrote:
> Jellby nous apporta ses lumieres ainsi en ce 2004/04/24 09:47... :
> 
>> Among other things, Alain tuvo wrote:
>>
>>> 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.
>>
>> But it's not necessarily constant, is it?
>>
>> 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.)
>>
> 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...

Then it's settled! Because the albedo of a surface is linear, then it 
can be expressed in terms of percentages :-)
-- 
Respectfully,
Dan P
http://<broken link>

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