Christopher James Huff wrote:

> In article <408c3d0f$1@news.povray.org>, Darren New <dne### [at] sanrrcom> 
> wrote:
> 
>>Haven't you heard of launching lasers and light sails? :-) Anyway, you 
>>*can* hold energy from absobed light indefinitely. That's what 
>>photosynthesis does.
> 
> But you can't continue to accumulate it indefinitely...for example, if 
> the stored energy were never used, plants would eventually run out of 
> CO2 and H20 to build the sugars which they store the energy in. You will 
> eventually reach some equilibrium where total input == total output. 
> However, if albedo includes radiation as well as reflection, then 
> objects like suns and gas giants have albedos greater than 1.

Albedo does not include radiation by definiton. An object that emits 
light radiation, like a sun, is the light source!

Also, if you count radiation outside of the visible spectrum, an albedo 
will be a fraction of /all/ of that radiation, including the visible 
stuff, which would /still/ be a value between zero and one.

> Also, albedo could be used to refer specifically to visible light...in 
> which case it would actually be possible for the reflective albedo to be 
> greater than 100%, due to fluorescent materials on the surface. 
> Extremely unlikely on a dead rock, though a planet with a large amount 
> of fluorescent plant life could do it naturally.

Such materials emit light and, therefore, cannot be a valid part of an 
albedo value by definition. Albedos only concern /reflected/ light. If 
an albedo value is above 1, it is an error -- it is not a /valid/ value; 
it means that there is emissive material on the surface or a flaw in the 
instrument that is reading the value.
-- 
Respectfully,
Dan P
http://<broken link>

Post a reply to this message