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Why is the sky blue?

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Re: Why is the sky blue?

#151

Post by robocat »

jstummbillig wrote: post #74
staplung wrote: post #18

In The Cuckoo's Egg Cliff Stoll recounts an episode from the oral defense of his astrophysics PhD thesis. A bunch of people ask questions but one prof holds back until... """ “I’ve got just one question, Cliff,” he says, carving his way through the Eberhard-Faber. “Why is the sky blue?” My mind is absolutely, profoundly blank. I have no idea. I look out the window at the sky with the primitive, uncomprehending wonder…

I am positively excited about the upcoming first generation of humans who will have all their questions answered, correctly and in the way they can best understand, and as often and many of them as they want – and what that is going to enable.

I childishly looked for a historical quote on how we should all be doing science at home now. Google referred me to a gorgeous article written by Isaac Asimov:

   While computers and robots are doing the scut-work of society so that the world, in 2019, will seem more and more to be “running itself,” more and more human beings will find themselves living a life rich in leisure.

  This does not mean leisure to do nothing, but leisure to do something one wants to do; to be free to engage in scientific research, in literature and the arts, to pursue out-of-the-way interests and fascinating hobbies of all kinds.
Fortunately our good friends at the Public Gaming Research Institute have republished the article originally published in the Toronto Star where Asimov imagined the world 35+ years in his future.

Unfortunately the link seems to contain some advertisements so perhaps google yourself to find a better source. I looked for a filetype:pdf but that didn't help me (although Gemini AI did helpfully summarise the same article).

We are definitely fortunate to live in a world with free access to information.

Unfortunately my skills at search are getting rusty.

Re: Why is the sky blue?

#152

Post by reactordev »

daedrdev wrote: post #141
reactordev wrote: post #99

Earlier quoted context omitted.

The real question is, is the sky blue for everyone? Some creatures can see ultraviolet. Some lack color at all…

Some animals have more cone types than humans, especially various birds, so would probably see a violet sky. We don't have this because common ancestor for all mammals lost all cones but one, perhaps due to being nocturnal, and a second was re-evolved as mammals became more dominant (after dinosaur extension). A third cone was evolved in primates due to a gene duplication that gave us our green cone https://www.scien…

maybe in 100M years we'll get a 4th cone or rod. Probably from nuclear mutation...

Re: Why is the sky blue?

#153

Post by reactordev »

mncharity wrote: post #123
reactordev wrote: post #99

Earlier quoted context omitted.

The real question is, is the sky blue for everyone? Some creatures can see ultraviolet. Some lack color at all…

I puttered on a color interactive where, to emphasize this distinction between world-spectra vs brain-color, you could swap in color deficiencies, a non-primate mammal ( dichromats), and a monochromat.

this is fascinating because I'm red/green color deficient yet I have no problem seeing most reds or greens. I feel there's a "spectrum" of color that we all see and each of us is slightly different. My shade of green may not be your shade of green. Yet, when I point out my shade of green - it matches your shade of green because of our eyes. Even though we may be perceiving entirely different colors.

Re: Why is the sky blue?

#154

Post by thaumasiotes »

srean wrote: post #73
smlavine wrote: post #70

Earlier quoted context omitted.

"tell"?

Ah! That's not bad but it's not the same thing. Good nevertheless. I can 'show' (or point someone to a) a sight that I am not myself creating in anyway. The word I am looking for would mean to 'make you hear' in the same may to show is to make you see. I showed him the distant tower. I ??? him the faint sound.

You appear to be looking for the word show, which is not specific to visual phenomena.

Re: Why is the sky blue?

#155

Post by goatlover »

kazinator wrote: post #145

> To get something purple, you’d need to find a material whose electrons were excited by low-energy red photons, but had no use for higher-energy violet photons. Nope! Purple is not violet! It a color that the eye perceives when stimulated by both blue and red wavelengths at the same time; there is no wavelength that produces purple by itself.

I think this and other facts about how we see color demonstrates that colors are not out there in the world, but rather a conscious perception of how we see the world, with animals having varying color schemes, some colors which we don't see, depending on their eyes and brains.

Why should only visible EM radiation have colors, but not radio, X-rays, etc?

Re: Why is the sky blue?

#156

Post by wasmperson »

KellyCriterion wrote: post #5

Interesting here is: Actually, for most blue butterflies, it’s not even a pigment-it’s just a trick of the light. Since blue is so rare in the biological world (hardly any plants or animals can produce real blue chemicals), they evolved structural colors. Their wings have these microscopic ridges that reflect blue light while canceling out other colors. It’s basically the same reason the sky looks blue, just built in…

Another great example of "structural" blue that can be created artificially by heating steel:

https://www.youtube.com/watch?v=NhjiIPohUyw

Re: Why is the sky blue?

#157

Post by sixo »

Here's one: why does sunlight appear "sharper" or "harsher" during cold winters?

The reason, I believe, is that cold air tends to be drier, and drier air scatters less, leading to more of the overall flux you receive coming straight from the sun rather than from the diffuse source of the sky around you. But I'm not certain of this.

Re: Why is the sky blue?

#158

Post by goatlover »

reactordev wrote: post #99
SAI_Peregrinus wrote: post #71

Earlier quoted context omitted.

It also needs a bit of biology. Our eyes don't have a flat response over frequency, they're more sensitive to blue than violet. Violet gets scattered even more than blue, and the violet light does shift our perception of the color. But it does so less than it would if we had photoreceptors more sensitive to violet , so the resulting perceptual color depends not just on the intensity of the light at different frequenc…

The real question is, is the sky blue for everyone? Some creatures can see ultraviolet. Some lack color at all…

How would Lieutenant Geordi La Forge from ST Next Generations see the sky with his visor?

Re: Why is the sky blue?

#159

Post by AlotOfReading »

reactordev wrote: post #153
mncharity wrote: post #123

Earlier quoted context omitted.

I puttered on a color interactive where, to emphasize this distinction between world-spectra vs brain-color, you could swap in color deficiencies, a non-primate mammal ( dichromats), and a monochromat.

this is fascinating because I'm red/green color deficient yet I have no problem seeing most reds or greens. I feel there's a "spectrum" of color that we all see and each of us is slightly different. My shade of green may not be your shade of green. Yet, when I point out my shade of green - it matches your shade of green because of our eyes. Even though we may be perceiving entirely different colors.

Most colorblind people aren't dichromats, they're so-called anomalous trichromats. Basically, the genes coding opsins in your eyes have a number of functional sites that tune the spectral sensitivity. Those sites are tuned as far apart as they can be in color-normal humans. Anomalous trichromats usually have a genetic error that causes their opsins' sensitivity curves to overlap more, which manifests as reduced color sensitivity.

Re: Why is the sky blue?

#160

Post by interroboink »

I went down this rabbit hole a while back — there's a fascinating history of various scientists' investigations into the blue sky, across many decades, with some back-and-forth between Russia and Europe. Einstein eventually made a connection between it and the seemingly-unrelated issue of "critical opalescence," by showing that the fluctuations of densities is responsible for the scattering, not just a simple "individual molecules floating in space" analysis that Rayleigh originally performed. But funnily, for an ideal gas (such as our atmosphere), the formula works out to be the same.

So, "Rayleigh scattering" is the common term still used today, but there is a deeper reason for the formula being correct — it remains correct even when molecules are relatively close together, such as in the lower layers of our atmosphere.

I found this nice paper[1] giving an overview of the timeline, various discoveries, etc: http://users.df.uba.ar/bragas/Web%20roberto/Papers/sobelman%...

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