[HN Gopher] Why is the sky blue?
___________________________________________________________________
Why is the sky blue?
Author : udit99
Score : 334 points
Date : 2026-02-09 15:39 UTC (7 hours ago)
(HTM) web link (explainers.blog)
(TXT) w3m dump (explainers.blog)
| ranger_danger wrote:
| Here is a wonderful lecture with real-world demonstrations of the
| effect:
|
| https://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?
| AndrewKemendo wrote:
| Fs is the frequency at which whatever your measuring is most
| efficient at vibrating
|
| So it's a combination of the composition of the thing and the
| environmental coupling with other vibrating things
|
| Size and material composition are the primary factors
|
| So for this case, the photon spectrum interact with nitrogen-
| oxygen mixture most efficiently at the frequency that reflects
| blue
|
| I mostly studied sound frequency mixing with static objects
| (matching or cancelling the fs of room/space with the fs of a
| driver) but the principles of resonance hold across media
| pfdietz wrote:
| Air molecules are much smaller than the wavelength of visible
| light, by several orders of magnitude. This is why you can't
| resolve individual molecules in an optical microscope, and why
| photolithography with visible light doesn't go down to
| molecular feature sizes.
| renewiltord wrote:
| https://www.youtube.com/watch?v=4a0FbQdH3dY&t=2038
|
| Direct link to timestamp 33:56
| dave_sid wrote:
| It's not. It's raining here.
| KellyCriterion wrote:
| 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
| Sharlin wrote:
| Not just butterflies, birds too! But what selection pressure
| drove the evolution of these structural colors? Presumably
| signaling, the opposite of muted, camouflaging colors.
|
| Also, as many might know, blue eyes are the result of a lack of
| pigment (eumelanin). The iris is translucent, but Rayleigh
| scattering preferentially backscatters blue photons. Green eyes
| have some pigment, making them a mix of brown and blue.
| adrian_b wrote:
| Also the blood veins that you see as bluish through the skin
| are blue for the same reason, due to light scattered in their
| walls.
| varispeed wrote:
| I thought they are green.
| SAI_Peregrinus wrote:
| Definitely more blue/purple.
| jjtheblunt wrote:
| It's also the trick employed by Iridigm, which Qualcomm
| acquired in late 2004 (i was there then).
|
| https://en.wikipedia.org/wiki/Interferometric_modulator_disp...
| amelius wrote:
| I'm curious how they were able to patent a technique invented
| by nature millions of years ago.
| jjtheblunt wrote:
| the displays have an array of switchable mirrors
| individually addressable, unlike nature in this case.
|
| (but sort of like chromophores in an octopus or cuttlefish,
| perhaps).
| amelius wrote:
| I see, but those MEMs mirrors were already invented.
| moron4hire wrote:
| Inventions can be useful recombinations or applications
| of other inventions. They don't need to be wholly unique
| unto themselves. Indeed, the vast majority of them are
| not wholly unique.
| amelius wrote:
| We're talking about a millions year old invention here.
| RupertSalt wrote:
| Obligatory xkcd: "Sky Color" https://m.xkcd.com/1145/
|
| Obligatory xkcd[2]: "Rayleigh Scattering"
| https://m.xkcd.com/1818/
|
| Others?
| margalabargala wrote:
| The "Rayleigh Scattering" comic is really spot on.
|
| Air is blue. The reason air is blue is blah blah blah physics,
| see the article we're all commenting on, but at the end of the
| day air is blue. We don't demand the same elaborate physics
| questions for why a ripe banana peel is yellow.
| zokier wrote:
| Not really. If the explanation was "air is blue" then the
| naive expectation would be that sun would appear blue against
| blackish background, basically the image of sun is being
| filtered through the atmosphere; if sun is white and air is
| blue then white filtered through blue should be blue? But sun
| appears yellowish against blue background. So clearly
| something different is going on.
| lovecg wrote:
| Though is some cases it is a very interesting question, like
| why gold and copper the color they are instead of being
| boring and silvery like all the other metals?
| gh5000 wrote:
| But a banana is yellow for a very different reason (and a
| much easier to explain reason) than why the sky is blue. And
| air isn't blue, because it's red at the end of the day?
| justin_dash wrote:
| For the sunset example then, a natural question (for me) is then
| why isn't the sky _green_ in the transition from blue sky to red
| sunset sky?
| teraflop wrote:
| Because the color of the sky is determined by a shifting
| _mixture_ of wavelengths, not a single shifting wavelength.
|
| Basically, the scattering process that "remove" blue from the
| spectrum also removes green, albeit to a lesser extent. There
| are _some_ greenish and yellowish wavelengths in the sunset
| sky, but they 're dominated by red, so the overall color
| appears red or orange.
|
| In order for the sky to look noticeably green, there would have
| to be something that scattered reds _and_ blues, without
| significantly absorbing green.
|
| If you try to interpolate between sky-blue and orange using
| graphics software, the result depends on what "color space"
| you're using. If your software interpolates based on hue, you
| might see green (or purple) in the middle. But that's not
| physically realistic.
|
| A realistic model is to interpolate each wavelength of the
| continuous spectrum separately. Interpolating in RGB color
| space is a crude approximation to this. And if you try the
| experiment, you'll see that the midpoint between sky-blue and
| orange is a kind of muddy brown, not green.
| photonic37 wrote:
| Your intuition isn't far off; there is an angle where the
| weight of green relative to the sum over wavelengths sees a
| local maximum. But it doesn't dominate. In that transition
| zone, there is still an overlapping, transitioning abundance of
| redder and bluer wavelengths, adding with the green.
| Consequently, you see red, going into a red+green transition
| (== oranges, yellows), go into into a green+blue transition (==
| cyan), which already has few photons relative to the red and
| yellow zones, so it's a dark/weak cyan, before it blends into
| the darker blue of the night sky.
| adornKey wrote:
| You won't get a green sky, but at least there is a
| meteorological optical phenomenon called the green flash around
| sunset. To see it, I think, you have to know what you're
| looking for - and you need good conditions.
| michael1999 wrote:
| It can be - https://en.wikipedia.org/wiki/Green_flash
| s0rce wrote:
| That's refraction not scattering though.
| seanalltogether wrote:
| Blue + Green + Red = White
|
| 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.
| jonahx wrote:
| 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.
| jph00 wrote:
| No, your job is to help your reader get to the end of the text.
| That means writing in a way that most of your audience finds
| compelling, readable, and not intimidating.
|
| Not all readers are the same, so you will fail at your job for
| some readers.
|
| But few readers are emotionless automatons that need nothing
| but dry technical content, unless it's a topic they are very
| motivated to understand.
| jonahx wrote:
| > That means writing in a way that most of your audience
| finds compelling, readable, and not intimidating.
|
| I would agree with that. And I think emojis and unnecessary
| reassurances subvert that goal. It's fluff, it's more to
| read, and if the writing isn't already clear, they don't fix
| the problem.
|
| > But few readers are emotionless automatons that need
| nothing but dry technical content
|
| Nothing in my post argues for dry technical content.
|
| Bartosz Ciechanowski's superb work, which may have inspired
| the author, gets the balance just right without any hand-
| holding asides:
|
| https://ciechanow.ski/mechanical-watch/
| nemo1618 wrote:
| 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.
| IceCoffe wrote:
| Our lord Zeus always thinks of everything
| dekhn wrote:
| His noodly appendage touches all.
| adolph wrote:
| > thought it was a pretty color
|
| So was blue intrinsically pretty and thus made into the sky, or
| considered pretty and thus imprinted in the minds of humans
| that way?
| staplung wrote:
| 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...
| """
| ecshafer wrote:
| "Could you be more specific" is a great question to find out
| more what the person knows and how they thing. You give an
| answer that, just due to the nature of knowledge and the
| limitation of language, has some black boxes. And "could you be
| more specific" is basically asking to go through the black
| boxes.
|
| Its like asking how does Java work or something like that? You
| can go from "The JVM interprets java byte code" to quite a lot
| of depth on how various parts work if you have enough
| knowledge.
| leeoniya wrote:
| i used something like this in unstructured technical
| interviews all the time.
|
| "you type a phrase into google search, you press enter, get
| some results. tell me, in technical detail, what happened in
| that chain of actions"
|
| the diversity of replies is fascinating, you learn a lot
| about a "full stack" candidate this way.
|
| Feynman's classic "Why?" chain:
| https://www.youtube.com/watch?v=36GT2zI8lVA
| SAI_Peregrinus wrote:
| I'd probably spend at least 20 minutes just to get through
| how the keyboard works, much more if it's a USB-HID device.
| dmd wrote:
| Hah - that is exactly what I did. Someone asked me this
| question and after 5 minutes in the weeds of the debounce
| on the mouse click they said "look all we wanted was to
| find out if you'd ever heard of DNS, let's move on, that
| was great".
| leeoniya wrote:
| the good ones would usually follow up with, "how much
| detail do you _really_ want ;D"
| HPsquared wrote:
| It's reminds me of that scene from Fargo: "He was kinda funny
| lookin'" ... "Could ya be any more specific?"
| SAI_Peregrinus wrote:
| 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
| frequencies but also on our particular biology. People with
| tritanopia (blue-yellow color blindness) don't have blue-
| sensitive cones (S cones) and thus to them _there is no
| perceived blue_. Not to mention the linguistic history of the
| word "blue" and why English uses "blue" instead of "Qing " or
| some other word, the questions around qualia & what it means to
| perceive color, etc.
| reactordev wrote:
| The real question is, is the sky blue for everyone? Some
| creatures can see ultraviolet. Some lack color at all...
| jstummbillig wrote:
| 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.
| brabel wrote:
| The same anticipation of great things happening preceded the
| arrival of widely available internet, but all we really got
| was cat videos initially, and doomscrolling more recently. I
| don't have much hope for great things anymore.
| reactordev wrote:
| We got more than that. We got 24/7 surveillance.
| ryanmcbride wrote:
| Me too but I don't think these sorts of Solved Society
| endgames are likely to show up. Basically presents the same
| issue with a utopia.
|
| Progression and regression are always going to be at war with
| each other. There will always be humans that want to hurt
| instead of help, there will always be humans who TRY to help
| but ultimately hurt. There will always be misinformation,
| there will always be lies, and there will always be liars.
|
| The good news is there will also always be people trying to
| pull humanity forwards, to help other people, to save lives,
| to eradicate disease, educate, and expose the truth.
|
| I don't think society will ever be solved in the way you're
| saying because there will always be hurtful people, but there
| will also always be good people to keep up the fight.
| kakacik wrote:
| ... and due to that, people will not appreciate all the
| knowledge, we will take it as air - invisible but cut the
| access in a myriad ways and its a catastrophe.
|
| We value what we achieve with effort, I would say
| proportionally to energy put in (certainly true for me, thus
| I like harder efforts in activities and ie sport climbing).
| Starlevel004 wrote:
| When is that going to be?
| archildress wrote:
| Anyone else immediately think of this commercial?
|
| https://www.youtube.com/watch?v=PbKsC4GCT5k
|
| *Since blue is the shortest wave length...*
| retroflexzy wrote:
| 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?_
| erikdkennedy wrote:
| Yes! This is _exactly_ why I wrote this article :)
|
| Any other questions give you the same disappointment?
| beders wrote:
| How can light "bounce off" something if it doesn't have mass?
| alejohausner wrote:
| Air is mostly nitrogen. Nitrogen gas is blue.
|
| There.
| pbhjpbhj wrote:
| Go watch a video of nitrogen gas evaporating from liquid
| nitrogen ... tell me what colour you see?
| mjanx123 wrote:
| Oxygen is blue actually. That only contributes to the sky
| blueness a little tho.
| TuringNYC wrote:
| Brilliant explanation and beautifully presented. I wish I had a
| technical writer who could write up our business case this well!
| erikdkennedy wrote:
| I'm the writer of the article, and happy to chat. Email is my
| username at gmail.
| liquidise wrote:
| Your blog layout, particularly on desktop, is brilliant.
| erikdkennedy wrote:
| My day job is UI design, so I especially appreciate this
|
| (Is there something in particular you're referring to? I
| feel like sticky nav and sidenotes aren't particularly
| unusual?)
| codeulike wrote:
| 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.
| jonahx wrote:
| https://www.youtube.com/watch?v=yV-KiTAAcrY
| numpad0 wrote:
| 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.
| signa11 wrote:
| didn't cv raman prove just that via his raman-effect for which he
| got the noble prize ?
| munificent wrote:
| Really cool article! Tangential:
|
| _> "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.
| erikdkennedy wrote:
| TIL!
|
| _Debates whether to update the sidenote with an explainer on
| ambitransitive and labile verbs_
| kazinator wrote:
| There are many verbs like this, and English is somewhat open
| toward using verbs that way, or becoming so.
|
| Did English speakers say "this novel reads well" two, three
| hundred years ago?
| suzzer99 wrote:
| Now do clam steamers and shrimp fried rice.
| srean wrote:
| I have always wondered about this. The verb for the first
| person is to 'see'. To a third person you 'show'
|
| For the first person there is 'listen' (or 'hear'). Does
| English not have a corresponding word for the third person ?
|
| What about Germanaic or Nordic languages ? Do they have a third
| person analogue of 'listen' ?
| smlavine wrote:
| "tell"?
| srean wrote:
| 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.
| ccozan wrote:
| play?
|
| I played him the faint sound.
| onestay42 wrote:
| AFAIK listen used to be used therefor[sic] but it has fallen
| out of use nowadays. From wiktionary:
|
| > Listen the watchman's cry upon the wall.
|
| Edit: formatting
| srean wrote:
| 'Hear the watchman's cry upon the wall' works the same way,
| no ?
|
| I have clarified what I am looking for in a cousin comment.
| tsoukase wrote:
| Labile verbs is a source of ambiguity of natural languages
| (only western ones?) that we are all accustomed to.
|
| The bell rang should become The bell was rung, either way it
| means The bell rang another bell.
| GuinansEyebrows wrote:
| "the bell was rung" illustrates a cause (and introduces a
| question: who rang the bell?)
|
| "the bell rang" illustrates an effect (the vibration and
| sound of the bell as it rings).
|
| i think this is more an illustration of the ambiguity of the
| root word "ring", which can be an action by a subject upon an
| object, or to describe the behavior of the object itself.
| rob74 wrote:
| 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!
| erikdkennedy wrote:
| There will be! Requests welcome!
|
| (I will almost certainly do one on quantum mechanics, but
| that's such a big explanation that I want to do some simpler
| ones first)
| aaroninsf wrote:
| Not discussed but should be:
|
| Prior to the great oxygenation event, Earth's sky was not blue;
| it was likely red-orange, carbon dioxide and methane being
| primary components.
| kazinator wrote:
| 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.
| Jun8 wrote:
| This was great as it went farther than Rayleigh scattering. On
| this topic you have to watch this fantastic undergrad physics
| lecture demonstration: https://www.youtube.com/watch?v=sJG-
| rXBbmCc&t=1674s
| oxag3n wrote:
| The same reason it's polarized.
| jama211 wrote:
| Brilliant, thank you
| deafpolygon wrote:
| Very well explained. I love the in-depthness of the article.
| FrogWizardMan wrote:
| to piss me off, goddammit
| halis wrote:
| Nitrogen.
| oxag3n wrote:
| I have a related but deeper question about sun and colors:
|
| Sunlight in space is considered white. When it reaches earth
| surface, it's considered a warmer color. Why human eyes that
| never (during evolution) saw sunlight without the atmosphere,
| consider it true white, and not colder color?
| zehaeva wrote:
| I think at this point you need to consider how the human eye
| see color. It's not like each wavelength gets picked up and
| then communicated perfectly.
|
| (I'm going to skip over some basic stuff, and use some
| generalities)
|
| Each Cone in the eye responds to a range of frequencies. This
| means that things that unless it's on the extreme low, or high,
| end of the frequencies that the human eye can discern you are
| going to have two, or all three, Cone types responding. The
| strength of those responses is what your brain uses to
| interpret the color that you see.
|
| The real problem is that out in space there is no attenuation
| of sunlight, it's bright. Super crazy bright. It basically
| overloads all of your Cones, and Rods, all at once, there is no
| way for your brain to find a signal of "oh there's more higher
| wavelengths here so interpret bluer than normal" because all of
| the signals got maxed out. If you max out all of the signals,
| you get white. It doesn't matter that in absolute terms there's
| more blue, the lower and mid frequencies are also maxed out.
| 16bytes wrote:
| Is it considered a warmer color on the surface?
|
| Mid-day sun in a clear sky is very white, in the 5k-6k color
| temperature range. It's hard to get a sense of how white it is
| because of how bright it is. In fact, the color temperature on
| the surface can be even higher than in outer-space!
|
| Compare this to a "warm" light bulb, which is around 2.5K.
| Sunrise/sunset is also around that range.
|
| Perhaps the "warm color" sun mindset comes from the only times
| that people can look directly at it. That is to say, around
| sunrise or sunset.
| mncharity wrote:
| Perhaps because one's world is often blue-lit? While whole-
| hemisphere illumination generalizes as warmer, local conditions
| vary. Absent _direct_ (yellow-ish) sunlight, outdoor daylight
| illumination can be quite blue-ish. I 've had fun recently with
| photos in a park under clear blue skies, shadowed by tall
| buildings... but with a gap, resulting in a narrow strip of
| bright sunlit ground. My phone will take a bit of sunlit snow
| as its whitepoint, and provide a blue-tinted world. Similarly
| for sunlit buildings in background.
| mvdtnz wrote:
| Some of the demonstrations are not working correctly, at least on
| my machine (Windows + MS Edge). Any demo with a "reference image"
| is not correctly updating the reference.
| yawpitch wrote:
| The sky isn't blue. It's transparent. That's why you can see
| stars that aren't blue at night. When struck by sunlight at the
| right angles it _appears_ blue, but saying it is blue is like
| saying the ocean is green when a bucket of it clearly isn't.
| awesomelybad wrote:
| Implementing an atmospheric shader in three.js is a fun way get
| an understanding of the interaction of the different scattering
| components, light, and observer's position. Plus you get a pretty
| cool effect to play around with after you're done.
| asqueella wrote:
| The explanation that made it click for me a while ago was by
| someone who implemented a shader
| https://www.alanzucconi.com/2017/10/10/atmospheric-scatterin...
| -- the explanations that don't end up producing an image all
| seemed to skip over one detail or another.
| mncharity wrote:
| > the explanations that don't end up producing an image all
| seemed to skip over one detail or another.
|
| Implementation can be wonderfully useful as both a test of,
| and a forcing function for, really understanding something.
| At least when groundtruth is available.
| 9dev wrote:
| So, does that mean, and bear with me here, that... air is blue?
| zkmon wrote:
| Okay, why does visible light have that range of frequencies?
| smegger001 wrote:
| because they are the frequencies that pass though water most
| readily, and we are made of mostly water
| jet98 wrote:
| that's interesting. I thought it was because our sun's
| spectrum has the most energy in visible light band -
| therefore we evolved to see the light which can give us the
| highest SNR.
|
| Can you be more specific?
| hintymad wrote:
| This level if geekiness is amazing. I hope more, a lot more,
| Americans can get into STEMS with this level of passion. It's sad
| that in the past few decades more and more people seemed to
| forget that STEM is a pillar of the modern civilization that we
| enjoy.
| IshKebab wrote:
| If you think about it "because air is blue when you look at it
| from the side" is about all the explanation we'd require if the
| sky was some normal object like an apple. Nobody asks "why is
| wood brown?" as if it's some deep question, but "why is the sky
| blue?" is somehow given greater gravitas, as if the reason is
| more mystical. I guess because the sky is so big and uniform?
| erikdkennedy wrote:
| It could also be this sorta thought:
|
| "There's air in my room, it appears transparent. The sky is
| made of air, it appears blue. Why the difference"
| Darkphibre wrote:
| I always loved this question when I played the 'Why' game with my
| kids: They ask why, and I'd ELI5. Then they'd ask why, and the
| process continued until I could excitedly say "We don't know for
| sure!! We think it might be XYZ, but we're still exploring that
| frontier."
| manojlds wrote:
| So are there animals that see a violet sky?
| thoughtlede wrote:
| I think we can simplify the answer to this question for most
| audience and say "the air is blue".
|
| If they say, the air appears to be clear when I stare at
| something other than sky, the answer is you need more of air to
| be able to see its blue-ness, in much the same way that a small
| amount of murky water in your palm appears clear, but a lot of it
| does not.
|
| If they ask, why don't I see that blue-ness at dawn or dusk, the
| answer is that the light source is at a different angle. The
| color of most objects changes when the light source is at a flat
| angle. And sun lights hits at a flat angle at dawn and dusk.
|
| If they ask, what exactly is the inside phenomenon to see the sky
| color to be blue, then explanations like this blog are relevant.
|
| If they ask, what exactly is a color, the answer is that it is a
| fiction made up by our brain.
| tehjoker wrote:
| This is a really great piece, the bit at the end showing why IR
| works in smokey environments and guessing the planet's
| composition based on color was really good.
| b_brief wrote:
| Good explanation of Rayleigh scattering, but I find many
| summaries miss that the scattering cross-section goes as
| wavelength, which is why blue light is so much more affected than
| red.
| thot_experiment wrote:
| the pupil asked, why is the sky blue? the master answered,
| because the sun is yellow, and the pupil was enlightened
| Night_Thastus wrote:
| This was both very informative, easy to understand, _and_ fun to
| read! That 's a winning combo. I now know a bit more about why
| the sky is the color it is.
|
| Thank you for making it. :)
|
| (The blog post, that is, not the sky. If you made the sky -
| please let me know!)
| mrb wrote:
| I dislike with passion the answer "because Rayleigh scattering".
| When someone asks why, especially if a child asks, the default
| answer should be the _simplest correct answer_ :
|
| Because it's the color of the atmosphere, specifically nitrogen
| and oxygen! It's technically correct to state this.
|
| Gasp! But aren't nitrogen and oxygen usually described as
| "colorless"? Well, yes but... If they were truly colorless, the
| sky would be black. It's technically more correct to describe
| them as _nearly_ colorless and very slightly blue. Very slightly
| because you need to see through kilometers of atmosphere to
| perceive the blue. It doesn 't matter if the color is caused by
| absorption, or reflection, or (Rayleigh) scattering of certain
| wavelengths. The "color" of an object is simply the color you
| perceive with your eyes. If you perceive blue, it's technically
| correct to say its color is blue.
|
| It's like saying plants are green because green is the color of
| chlorophyll. And in the case of chlorophyll, the color is caused
| by absorption not by scattering. But the physics is irrelevant.
| Green is its color.
|
| Q: But sunsets/sunrises are red & orange not blue! A: the
| simplest answer is: color of an object can change under different
| light conditions. Specifically in this example, when seeing the
| sun through not kilometers but hundred of kilometers of
| atmosphere, all the blue-ish wavelengths have been scattered in
| random directions so only the red-ish wavelengths remain, thus
| the atmosphere is illuminated by progressively redder and redder
| light as the photons travel longer and longer distances through
| the atmosphere.
| librasteve wrote:
| Why is the sky black?
|
| - at night (of course)
|
| - there are ~1 septillion stars that are all shiny
| alexander2002 wrote:
| This post is so good! You are a hero.
| nephihaha wrote:
| Where I live, the sky is grey much of the time... Most of last
| week anyway!
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