On Thu, Jun 07, 2018 at 10:05:34AM -0400, John Clark wrote: > On Wed, Jun 6, 2018 at 11:26 PM, Brent Meeker <[email protected]> wrote: > > > *> hasn't the Sun been getting hotter, which would mean moving from yellow > > toward green rather than the other way. And it's still still more a yellow > > than green store. * > > > There are intensely red stars and there are pale blue stars but there are > no green stars; the reason has to do with the fact that curve of blackbody > radiation energy output verses color of an object at a given temperature is > NOT symmetrical. It also has to do with the fact that the eye has 3 > different receptors for color, one for the red, green and blue. A star that > gives off the peak of its energy in the red will still give off a > substantial amount of energy in the infrared but the eye can't see that, > and due to the non-symmetrical blackbody curve the energy drops off rapidly > in the green and blue part of the spectrum, so only (or almost only) the > red receptor in the eye is stimulated so we see it as intensely red. > > A hotter star that gives off most of its energy in the blue would still > give off a lot in the red and green so all 3 receptors would be stimulated > and we'd see it as white, or if it was very very hot a bluish white (the > output would drop off rapidly in the ultraviolet but we can’t see that so > it doesn’t matter). Due to the shape of the blackbody curve there is no > temperature that would give off its radiant energy in the green but none in > the red or blue so that only the green receptor is stimulated. You can have > green lasers but unlike stars that light is not produced by blackbody > radiation, and because only the green receptor is stimulated it looks > intensely green. > > John K Clark >
The appearance of colour is as much psychological as anything. We would have evolved to perceive ambient light as white - doesn't matter whether there are clear skies, or it is cloudy, the brain will adjust, given appropriate cues. When we look at the sun, some of the blue light is scattered, giving the sun a yellow appearance. When the sun is closer to the horizon, the rays pass through more of the atmosphere, scattering even more of the the blue and green parts of the spectrum, so the sun appears a deeper red. That infamous dress from a couple of years ago shows what happens to our perceptions when cues about the ambient light is removed. Anyway, if your photosynthetic apparatus absorbed at a single frequency which you can adjust, you would set it to absorb at 500nm (green), which is the peak of the sun's spectrum. This appears to be what evolution did with cyanobacteria, giving its purply-red colour. Of course it would be better to absorb the whole spectrum, and appear black, but evolution is not omnipotent :). Cheers -- ---------------------------------------------------------------------------- Dr Russell Standish Phone 0425 253119 (mobile) Principal, High Performance Coders Visiting Senior Research Fellow [email protected] Economics, Kingston University http://www.hpcoders.com.au ---------------------------------------------------------------------------- -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at https://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/d/optout.
