Among other things, Alain wrote:

> 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.

OK, If you say so I believe you.

BUT, from other scientific courses and past experience I've learnt that 
things are often not so simple. Sometimes it is convenient to express 
quantities as quotients between other quantities, so that you have a number 
which will, hopefully, remain constant. Sometimes this number is constant 
only in a certain range of conditions (for example, the "rate constant" of 
chemical reactions is not constant, it changes with the Temperature; the 
"absorption coefficient" of Lambert-Beer's Law is constant in a range of 
concentrations, but not outside it).

So, I believe this could well be the case of albedo. Maybe, given the set of 
conditions usually found in the solar system, we can take the fraction of 
the incident radiation being reflected as constant for a given body. But 
this doesn't mean it *has* to be constant, it could change with extremely 
high or low light intensities. I believe this is a valid concern, given the 
way the real world behaves.

-- 
light_source{9+9*x,1}camera{orthographic look_at(1-y)/4angle 30location
9/4-z*4}light_source{-9*z,1}union{box{.9-z.1+x clipped_by{plane{2+y-4*x
0}}}box{z-y-.1.1+z}box{-.1.1+x}box{.1z-.1}pigment{rgb<.8.2,1>}}//Jellby

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