All I’ve said is that a cloud is a WHITER object than the direct sunlight that wasnt scattered/whatever and is a better representation of the actual color of the sun. Of course all this assumes that a cloud is a reasonably spectrally neutral reflective body.
I guess clouds are actually “bluer” if you insist that the definition of white depends only on what direct sunlight that reaches the ground is. But, again, the cloud is closer to the “true” color of the sun. And nobody that I know of refers to blue clouds. And I touched on the definition of the whole “white” thing from the very beginning.
No – you said that the Rayleigh scattering taking out the blue makes the sun appear yellow:
That’s what I’m disputing – the amount of blue removed via this scatter is negligible, and doesn’t noticeably affect the color of the sun. Again, Plaitt and others have noted this in the past. The apparent yellow color of the sun has a different cause. Differences in the color of clouds due to added Rayleigh scatter is also negligible.
As for the sun appearing yellow by contrast with the blue sky, I note that nothing else white appears to be yellow when compared to the blue sky – White sheets on a line, white houses, white sails on sailboats, or a white sheet of paper. Or, of course, those white clouds – all of them are easy to look at (unlike the bright sun) and yet nobody perceibves them as yellow. Why should the sun be any different? There’s no reason to think that it appears yellow because of a contrasting blue sky.
If you don’t believe it, try looking at a white piece of paper against a sky-blue background with a white light source (ideally the sun – tungsten, as noted above, is yellowish) and see if it looks yellower against a blue backdrpop than against a white or neutral gray one.
Laundry cleaners use “whiteners” which are actually bluing agents - they make the color more blue so that we perceive them as more white. Failure to use bluing agents results in … yellow looking whites.
The fact that the Sun’s so bright also has to have something to do with it, since the Moon is the same color as the Sun, and is subject to the same atmospheric effects, but is not regarded as yellowish.
Though it does sometimes look yellow. I think I remember it looking that way when I was in Africa. Also, it can be quite orange/yellow during a lunar eclipse. (Whilst a solar eclipse surrounds it with blue light).
Why exactly does this happen? CalMeacham, your explanations have been interesting.
Yes, but it’s mostly significant near sunrise and sunset, not in midday. The blue you see in the sky is the blue that’s lost from someone else’s sunset.
And think about it. You have a whole one pie steradian of solid angle of bright blue easily visible sky up there shining down on you. Thats about 60 thousand times the solid angle of the sun if my envelope is right.
And there is breaking news from our esteemed research lab but right now the quality assurance department is reviewing the data.
Long story short. My camera and eyes see direct sunlight only as noteably “more yellow/less blue” than a white piece of paper in direct sunlight AND exposed to that whole big beautiful blue sky.
Is it so obvious a blind man could see it? No. Is it so subtle that I can barely tell if I lie to myself mentally?No.
Its there.
If you wanna know roughly what color the sun looks like from space, look at white cloud on clear blue sky day. That, climb Everest in a space suit, or catch a ride on the Shuttle.
One reason that the sun is always depicted as yellow is that when you’re in kindergarten and you’re drawing that picture of your house with the people with the stick hands and the sun upinna sky with the rays coming out of it, you couldn’t draw it very well on white paper with a white crayola. So, astronomers decided many years ago, in the Pestalozzi-Froebel equation, to declare the sun yellow. And so it stands to this very day.
Sorry, I missed this reply earlier. I’ll let Chronos explain his own words if he wishes.
The point, though, is that you are seeing the blue light. That light obviously cannot be coming at you directly from the sun, since it’s been scattered and clearly visible from somewhere other than the sun in the sky. Therefore that light, at least, cannot be part of what you perceive to be the color of the sun when you look at it (assuming you could do so safely), nor could it have been ‘lost’ from that view of the sun. It’s the people far away that that light was directed at, but scattered towards you. So it make some sense to say it’s ‘missing’ from their view of the sun; most pronounced at their dawn or dusk, but in fairness any other point away from you will do.