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 into a wing. If you were to look at the wings from a different angle or get them wet, the blue often disappears because you're messing with that physical structure
I wonder if the interference-based-blue of the morpho butterfly evolved because it's difficult to make blue pigment for some reason having to do the chemistry of our biosphere, or if it's an evolutionary response to humans who may have captured the blue ones and ground them up for pigment (much like we did with https://en.wikipedia.org/wiki/Tyrian_purple snails).
I'm not aware of any record of us having done so, but it's absolutely the kind of thing we would do, and there's much more pre-history than history when it might've happened.
That is the natural transition from overhead sun to sunset as each higher energy wavelength gets cut off more and more. When blue is mostly gone and green starts to fade we call it the Golden Hour.
Going to be that guy, even though I think this is a really nice work overall...
But the winking and "cool guy" emojis are so grating. In general, technical explanations that apologize for themselves with constant reassurances like "don't worry" and "it's actually simple" undermine their own aim.
Your job -- if you're making content for people with double digit ages -- is to make the explanation as clear as you can, not to patronize and emotionally hand-hold the reader.
Let's be real. The sky is blue because God thought it was a pretty color, simple as. All this stuff about wavelengths and resonant frequencies and human color perception got retconned into the physics engine at some point in the past millennium, that's why all these epicycles are needed.
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 of a Neanderthal contemplating fire. I force myself to say something—anything. “Scattered light,” I reply. “Uh, yeah, scattered sunlight.”
“Could you be more specific?”
Well, words came from somewhere, out of some deep instinct of self-preservation. I babbled about the spectrum of sunlight, the upper atmosphere, and how light interacts with molecules of air.
“Could you be more specific?”
I’m describing how air molecules have dipole moments, the wave-particle duality of light, scribbling equations on the blackboard, and . . .
“Could you be more specific?”
An hour later, I’m sweating hard. His simple question—a five-year-old’s question—has drawn together oscillator theory, electricity and magnetism, thermodynamics, even quantum mechanics. Even in my miserable writhing, I admired the guy…
"""
A great story, though it seems a little odd to me since Rayleigh scattering was covered in my undergrad exoplanets course. I'd expect an astrophysics PhD to have a better first answer than "scattered sunlight".
Back in my youth, after the Internet became common but before Wikipedia, I tried to discover the answer to this and came away disappointed again and again. Every article I could find simply stated "because light scattering", and barely much more.
How does scattering work? Why does light scatter? _What does scattering even mean in the context of light?_
In terms of "qualia", its the other way round probably? Like the way we see colours would have evolved (within the available environment of wavelengths and scatterings and the possibilities with rods and cones) so that the things we want to see are more likely to stand out. So we see the sky as blue because leaves are green and berries are red.
Funniest memory re: Rayleigh scattering: in anime show Aldnoah Zero, the uber-genius protagonist mansplains about it to a high profile girl, basically completely out of blue. An impostor of the girl later appears on an in-universe pirate broadcast, making an agitating environmentalism talking point using a technically incorrect explanation of the phenomenon that isn't consistent with the fact. The ever-right protagonist immediately notices it, having enlightened the girl previously on that exact topic, and it leads to actions.
Like, dude, as if anyone would care about such a highly technical point, like eg some React framework quirk or race condition mitigation for specific generation of Intel procesdor or a semi-well known edge cases with btrfs inode behavior, even if I had been on that exact camp.
Rayleigh scattering is elastic (only the direction changes), whereas Raman scattering is inelastic (energy, that is color changes in addition to direction) scattering.
> “Scattering” is the scientific term of art for molecules deflecting photons. Linguistically, it’s used somewhat inconsistently. You’ll hear both “blue light scatters more” (the subject is the light) and “atmospheric molecules scatter blue light more” (the subject is the molecule). In any case, they means the same thing
There's nothing ambiguous or inconsistent about this. In English a verb is transitive if it takes one or more objects in addition to the subject. In "Anna carries a book", "carries" is transitive. A verb is intransivite if it takes no object as with "jumps" in "The frog jumps.".
Many verbs in English are "ambitransitive" where they can either take an object or not, and the meaning often shifts depending on how it's used. There is a whole category of verbs called "labile verbs" where the subject of the intransitive form becomes the object of the transitive form:
* Intransitive: The bell rang.
* Transitive: John rang the bell.
"Scatter" is simply a labile verb:
* Intransitive: Blue light scatters.
* Transitive: Atmospheric molecules scatter blue light more.
Great article! I have to admit I had also heard of "Rayleigh scattering", but didn't really know more than that, until today.
Actually, I liked it so much that I went to the homepage of the blog, only to find out that this is the only article. Oh well... I hope there will be more to come!
It's also not just why the setting or rising sun is red, but why it's yellow when high in the sky. The sun doesn't look yellow when viewed from outside the atmospheric veil.
The article has a section on "why are clouds white?", but it doesn't really address the reason I thought that question should be covered.
It just says that clouds act like a collection of randomly-oriented prisms, such that whenever light of any wavelength comes into the cloud, it is dispersed from the cloud evenly in all directions.
This would explain why a cloud was white if even white light was coming into the cloud. But the rest of the article establishes that the light coming into the cloud is predominantly blue and purple. Why isn't that also true of the light leaving the cloud?
104 comments
[ 4.5 ms ] story [ 103 ms ] threadhttps://www.youtube.com/watch?v=4a0FbQdH3dY
https://en.wikipedia.org/wiki/Rayleigh_scattering
I do have a question though.
The article says:
> blue and violet have the closest frequencies to a “resonant frequency” of nitrogen and oxygen molecules’s electron clouds
I thought it was more to do with the photon frequency matching the physical size of the air molecules? Or is that the same as its resonant frequency?
It’s basically the same reason the sky looks blue, just built into a wing. If you were to look at the wings from a different angle or get them wet, the blue often disappears because you're messing with that physical structure
I'm not aware of any record of us having done so, but it's absolutely the kind of thing we would do, and there's much more pre-history than history when it might've happened.
https://www.youtube.com/watch?v=NhjiIPohUyw
Obligatory xkcd[2]: "Rayleigh Scattering" https://m.xkcd.com/1818/
Others?
The liquid air article on wikipedia doesn't have any photos.
https://en.wikipedia.org/wiki/Liquid_oxygen
Green + Red = Yellow
Red = Red
That is the natural transition from overhead sun to sunset as each higher energy wavelength gets cut off more and more. When blue is mostly gone and green starts to fade we call it the Golden Hour.
But the winking and "cool guy" emojis are so grating. In general, technical explanations that apologize for themselves with constant reassurances like "don't worry" and "it's actually simple" undermine their own aim.
Your job -- if you're making content for people with double digit ages -- is to make the explanation as clear as you can, not to patronize and emotionally hand-hold the reader.
""" “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 of a Neanderthal contemplating fire. I force myself to say something—anything. “Scattered light,” I reply. “Uh, yeah, scattered sunlight.”
“Could you be more specific?”
Well, words came from somewhere, out of some deep instinct of self-preservation. I babbled about the spectrum of sunlight, the upper atmosphere, and how light interacts with molecules of air.
“Could you be more specific?”
I’m describing how air molecules have dipole moments, the wave-particle duality of light, scribbling equations on the blackboard, and . . .
“Could you be more specific?”
An hour later, I’m sweating hard. His simple question—a five-year-old’s question—has drawn together oscillator theory, electricity and magnetism, thermodynamics, even quantum mechanics. Even in my miserable writhing, I admired the guy… """
https://www.youtube.com/watch?v=PbKsC4GCT5k
*Since blue is the shortest wave length...*
How does scattering work? Why does light scatter? _What does scattering even mean in the context of light?_
There.
Like, dude, as if anyone would care about such a highly technical point, like eg some React framework quirk or race condition mitigation for specific generation of Intel procesdor or a semi-well known edge cases with btrfs inode behavior, even if I had been on that exact camp.
Rayleigh scattering is elastic (only the direction changes), whereas Raman scattering is inelastic (energy, that is color changes in addition to direction) scattering.
> “Scattering” is the scientific term of art for molecules deflecting photons. Linguistically, it’s used somewhat inconsistently. You’ll hear both “blue light scatters more” (the subject is the light) and “atmospheric molecules scatter blue light more” (the subject is the molecule). In any case, they means the same thing
There's nothing ambiguous or inconsistent about this. In English a verb is transitive if it takes one or more objects in addition to the subject. In "Anna carries a book", "carries" is transitive. A verb is intransivite if it takes no object as with "jumps" in "The frog jumps.".
Many verbs in English are "ambitransitive" where they can either take an object or not, and the meaning often shifts depending on how it's used. There is a whole category of verbs called "labile verbs" where the subject of the intransitive form becomes the object of the transitive form:
* Intransitive: The bell rang.
* Transitive: John rang the bell.
"Scatter" is simply a labile verb:
* Intransitive: Blue light scatters.
* Transitive: Atmospheric molecules scatter blue light more.
If something "carries" or is "a carry", it means it is so strong it metaphorically carries the rest of the setup with it. For example:
> This card carries.
> These two are the carries of the team.
Actually, I liked it so much that I went to the homepage of the blog, only to find out that this is the only article. Oh well... I hope there will be more to come!
Prior to the great oxygenation event, Earth's sky was not blue; it was likely red-orange, carbon dioxide and methane being primary components.
It just says that clouds act like a collection of randomly-oriented prisms, such that whenever light of any wavelength comes into the cloud, it is dispersed from the cloud evenly in all directions.
This would explain why a cloud was white if even white light was coming into the cloud. But the rest of the article establishes that the light coming into the cloud is predominantly blue and purple. Why isn't that also true of the light leaving the cloud?