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Why is the sky blue?

2026-02-0915:39813270explainers.blog

Let’s start by asking ourselves: what color SHOULD the sky be? Or, one step further back, what color should anything be? And the answer is: the color of anything is due to the wavelength of photons…

Let’s start by asking ourselves: what color SHOULD the sky be?

Or, one step further back, what color should anything be?

And the answer is: the color of anything is due to the wavelength of photons coming from that thing and hitting your eye.

Well ackshually… 🧐

These sidenotes are optional to read, but I’ll use them for giving the fuller technical details when I’ve abbreviated things in the main body of the text.

In this case, the color you see is determined by the wavelengths of light entering your eye since (1) you may be seeing a pure frequency, but in almost all cases, (2) you’re seeing many frequencies, which your brain interprets as a single color.

For instance, the sensation of turquoise at a specific point can be caused by (a) photons of wavelength 500nm emanating from that point, (b) a specific combo of photons of wavelengths 470nm and 540nm, or (c) (mostly realistically) photons of a huge number of wavelengths, probably peaking somewhere around 500nm.

In the text, I am a bit fast and loose with the difference.

When sunlight hits Earth’s atmosphere, most colors of photons pass through unencumbered. But blue photons have a tendency to ricochet around a lot.

This causes them to disperse all throughout the atmosphere. They disperse so far and wide, and are so numerous, that you can look at any part of the sky on a clear afternoon and, at that moment, blue photons will be shooting from that point straight to your eyes.

Therefore the sky is blue.

Most colors of light pass through the atmosphere relatively unencumbered. You only see them when you look at the sun, where they contribute to the whiteness of the sun’s light. Blue, however, bounces around a lot, getting spread all over the sky. Because blue photons hit our eyeballs from every angle of the sky, the whole sky appears blue.

What’s so special about blue?

This is true and all, but it kicks the can down the road. Why blue? Why not red?

In short, it’s because blue and violet have the closest frequencies to a “resonant frequency” of nitrogen and oxygen molecules’ electron clouds.

There's a lot there, so we'll unpack it below. But first, here's an (interactive) demo.

When a photon passes through/near a small molecule (like N2 or O2, which make up 99% of our atmosphere), it causes the electron cloud around the molecules to “jiggle”. This jiggling is at the same frequency as the photon itself – meaning violet photons cause faster jiggling than red photons.

In any case, for reasons due the internal structure of the molecule, there are certain resonant frequencies of each molecule’s electron cloud. As the electron clouds vibrate closer and closer to these resonant frequencies, the vibrations get larger and larger.

(This is completely analogous to pushing a child on a swing at the “right” frequency so that they swing higher and higher)

The stronger the electron cloud’s oscillations, the more likely a passing photon (a) is deflected in a new direction rather than (b) passes straight through.

For both N2 and O2, the lowest resonant frequency is in the ultraviolet range. So as the visible colors increase in frequency towards ultraviolet, we see more and more deflection, or “scattering”.

In fact, violet is 10x more likely to scatter than red.

Chart showing amount of scattering increasing with the fourth power of frequency
Math talk: scattering increases proportional to the FOURTH power of the frequency. So higher frequency light means WAY more scattering.

So why isn't the sky violet? Great question – we'll cover that in a sec.

I just want to point out two other things that (a) you can see in the demo above, and (b) are useful for later in this article.

First, when light gets really close to – and eventually exactly at – the resonant frequency of the molecule’s electron cloud, it gets absorbed far more than scattered! The photon simply disappears into the electron cloud (and the electron cloud bumps up one energy level). This isn’t important for understanding the color of Earth's sky… but there are other skies out there 😉

Second, did you notice that even red scatters some? Like, yes, blue scatters 10x more. But the sky is actually every color, just mostly blue/violet. This is why the sky is light blue. If white light is all visible colors of light mixed together equally, light blue is all visible colors mixed together – but biased towards blue.

What would the sky look like if it was only blue? Check it out.

I'll just end by saying, this dynamic (where scattering increases sharply with the frequency of light) applies to far more than just N2 and O2. In fact, any small gaseous molecule – carbon dioxide, hydrogen, helium, etc. – would preferentially scatter blue, yielding a blue sky at day.

Why isn’t the sky violet?

As you saw above, violet scatters more than blue. So why isn’t the sky purple? The dumb but true answer is: our eyes are just worse at seeing violet. It’s the very highest frequency of light we can see; it’s riiight on the edge of our perception.

But! – if we could see violet as well as blue, the sky would appear violet.

We might as well tackle the elephant in the room: if we could see ultraviolet (which is the next higher frequency after violet), would the sky actually be ultraviolet?

And the answer is not really. If we could see UV, the sky would be a UV-tinted violet, but it wouldn’t be overwhelmingly ultraviolet. First, because the sun emits less UV light than visible light. And second, some of that UV light is absorbed by the ozone layer, so it never ever reaches Earth’s surface.

You can see both of those effects in the solar radiation spectrum chart:

Chart showing solar radiation as a function of wavelength, both for top-of-atmosphere values and sea-level values
The sun emits the most visible light, with UV frequencies falling off very steeply. Augmenting this effect is that the ozone layer in particular absorbs a lot of UV before it can reach Earth’s surface.

Why is the sunset red?

So the obvious next question is why is the sky red at dusk and dawn?

It’s because the sunlight has to travel through way more atmosphere when you’re viewing it at a low angle, and this extended jaunt through the atmosphere gives ample opportunity for allll the blue to scatter away – and even a good deal of the green too!

Simply put, the blue photons (and to a lesser degree, the green) have either (a) gone off into space or (b) hit the earth somewhere else before they reach your eyes.

Diagram showing blue light scattering fully at sunset, creating a red sky

When the sun is on the horizon (e.g. sunrise or sunset), the photons it emits travel through 40x as much atmosphere to reach your eyes as they would at midday. So blue’s 10x propensity to scatter means it’s simply gone by the time it would’ve reached your eyes. Even green is significantly dampened. Red light, which hardly scatters at all, just cruises on through.

Again, you can play with this and see for yourself 😎

Why are clouds white?

The answer to this question is the second of three “domains” you should understand in order to have a working model of atmosphere color. The physics are different from the small-molecule scattering above.

Clouds are made up of a huge number of tiny water droplets. These droplets are so small (around .02 millimeters in diameter) that they remain floating in the air. But compared to small gas molecules like N2 and O2, these droplets are enormous. A single water droplet may be 100 trillion H2O molecules!

So, it’s not as simple as “the photons cause the hundreds of trillions of electrons to jiggle”. Instead, it’s more like the light has entered a very tiny prism or glass bead.

A prism deflecting white light into a rainbow
In a prism, white light can reflect around, bounce off exterior or interior surfaces, and even reflect differently depending on frequency – creating a rainbow effect.

The droplet is just as complex. Some of the photons hitting the droplet bounce off the surface. Some enter it, bounce around inside once, twice, etc. – and leave again. Perhaps a few are absorbed. As with a prism, different wavelengths of light will reflect at different angles. The specifics aren’t important – you should just get the general gist.

The many paths of light through a water droplet

So whatever white (or slightly yellowish) light that came from the direction of the sun is leaving in many random directions. Think of every color, shooting off in different directions! And then multiply that by a quadrillion droplets! In sum, you just see every frequency of photon coming from every part of the cloud.

And that means the cloud is white!

This idea that the tiny droplets that comprise clouds scales up. Anything larger that light can enter – drizzle, raindrops, hail – will also tend towards white.

But that raises the question – what about things in between tiny molecules (N2, O2) and the relatively enormous prism-like droplets? How do those things act?

Well, the dust in the sky of Mars is a great example 😉

Why is the sky on Mars red?

The answer to this question is the third of three “domains” you should understand in order to have a working model of atmosphere color. The physics are different from both the small-molecule scattering and large-droplet prism-dynamics above.

The Martian sky is red because it’s full of tiny, iron-rich dust particles that absorb blue – leaving only red to scatter.

Yeah, yeah, I hear you. This answer is can-kicking! “Dust, schmust. Why does it absorb blue?”, you demand.

OK, so the answer is actually fairly straightforward. And it generalizes. Here’s the rule: whenever you have solid particles in the atmosphere (very small ones, approximately the size of the wavelength of visible light), they generally tend to turn the air warm colors – red, orange, yellow.

If you live in an area with wildfires, you’ve probably seen this effect here on Earth!

An orangish-brown smoke-filled sky above Palo Alto.
An orangish-brown smoke-filled sky above Palo Alto.

To really understand the reason, let’s back up and talk about some chemistry.

Compared to tiny gas molecules, solid particles tend to have a much wider range of light frequencies that they absorb.

For instance, we discussed how N2 and O2 have specific resonant frequencies at which they hungrily absorb UV photons. Move slightly away from those frequencies, and absorption drops off a cliff.

But even for a tiny dust nanoparticle, there are many constituent molecules, each in slightly different configurations, each being jostled slightly differently by its neighbors. Consequently, the constituent molecules all have slightly different preferences of which frequency to absorb.

Because the “peak” absorption of the molecules is usually violet or ultraviolet (as it is with small gases), blues/violets will make it to the surface much less than oranges/reds.

Approximate light absorption from Martian dust as a function of wavelength
Approximate light absorption from Martian dust as a function of wavelength

Of course, a reasonable question is why are blue and violet absorbed so strongly by these dust particles?

Well, those are the only photons with enough energy to bump the dust molecules’s electrons up to a new energy state.

(Reminder: a photon’s energy is proportional to its frequency. Higher frequency – e.g. violet – means higher energy, and lower frequency – e.g. red – means lower energy)

So, the exact specifics depend on the molecules in question, but generally, the level of energy needed to bump up the electron energy state in a dust or smog particle’s molecules corresponds to violet or UV photons.

This is actually true of solids in general, not just atmospheric dust or aerosols. If you’ve ever heard that purple was “the color of kings” or that the purple dye of antiquity was worth its weight in gold, it’s true! 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.

A Tyrian purple shroud of Charlemagne
A Tyrian purple shroud of Charlemagne

So this is why the Martian sky is red – and why reds and browns are more common in nature (for solid things, at least) than purple and blue.

Why is the Martian sunset blue?

It’s less famous than the red daytime sky of Mars, but the Martian sunset is blue!

Photo of Martian sunset with blue halo taken by the Spirit rover
Martian sunset photo taken by the Spirit rover.

Photo by NASA/JPL/Texas A&M/Cornell.

In the last section, we talked about Martian dust absorbing violet/blue. But the dust also scatters light – which it can do totally unrelated to how it absorbs (remember, since photons can – and usually do – cruise straight through a molecule, scattering and absorbing can have their own interesting frequency-dependent characteristics. They don’t simply sum to 100%)

Small atmospheric particles, like dust and smog, are equal-opportunity scatterers. The absolute probability they’ll scatter a photon does not change significantly with the photon’s wavelength. However, different-frequency photons can be more or less likely to scatter in different directions.

For our purposes, it suffices to know that Martian dust – like many atmospheric particles of similar size – generally scatters blue light closer to the direction it was already going. Red light has a higher probability of deflecting at a greater angle.

Diagram showing how the Martian sunset appears blue
Because red light deflects MORE and blue light LESS when scattering off dust particles, the area directly around the sun will be blue – even though more blue is absorbed en route.

When molecules deflect photons only a tiny angle, it’s called “forward scattering”. Forward scattering is the most pronounced for larger particles, like dust or smog aerosols. It’s actually so strong on Mars that even at midday, red light doesn’t fill the sky evenly – the sky opposite the sun is noticeably darker!

But blue’s tendency to forward-scatter more directly against Martian dust means the Martian sunset has a blue halo.

Building a model

At the beginning of this article, I said being able to predict something is a good measure of how well you understand it. Let’s do that now. Let’s build a model for predicting the sky color on new planets/moons, or during different scenarios on our own planet.

(Not the most practical thing, but a good nerdsnipe 🙂)

Here are the three general rules of thumb we’ve already talked about.

Small gas molecules = blue/green atmosphere

Atmospheric gases tend to be much, much smaller than the wavelengths of visible light. In these cases, they tend to preferentially scatter blue/violet/UV. This means that gaseous atmospheres are usually blue or blue-green.

Earth's blue sky
Earth: atmosphere is 99% nitrogen and oxygen.

Uranus' blue sky
Uranus: upper atmosphere is 98% hydrogen and helium. We don’t have pictures from the surface.

Patrick Irwin, University of Oxford.

Neptune's blue sky
Neptune: upper atmosphere is 99% hydrogen and helium. We don’t have pictures from the surface.

Patrick Irwin, University of Oxford.

This is pleasingly true for Earth, Uranus, and Neptune.

Dust or haze = red/orange/yellow atmospheres

When visible light hits particles that are in the ballpark of its own wavelength, things get more complicated and can differ on a case-by-case basis.

These particles are typically either:

  • Dust: solid particles kicked up by mechanical means (wind, volcanos, meteorites)
  • Haze: solid particles formed by chemical reactions in the atmosphere

Dust and haze generally makes atmospheres appear warmer colors – e.g. red, orange, yellow.

Mars' red sky
Mars: iron oxide dust.

NASA/JPL-Caltech/ASU/MSSS

Titan's orange sky
Titan (a moon of Saturn): haze of organic molecules.

ESA/NASA/JPL/University Of Arizona

Venus' yellow sky
Venus: haze of sulfurous molecules.

Russian Academy of Science, processing by Don Mitchell

All three significantly dusty/hazy atmospheres in our solar system hold to this rule!

  • Mars’s sky is red due to iron oxide-rich dust
  • Titan’s sky is orange due to a haze of tholins (organic molecules)
  • Venus’s sky is yellow to a haze of sulfurous compounds

Clouds = white/gray

When visible light hits clouds of droplets (or ice crystals) that are much bigger than light’s wavelength, the droplets act akin to a vast army of floating prisms, sending out all colors in all directions.

Consequently, clouds tend to appear white, gray, or desaturated hues.

(Provided the cloud is hit by white light from the sun, that is. If a cloud is below a thick haze or doesn’t receive all wavelengths, neither can it reflect all wavelengths)

Earth's white clouds
Earth: clouds made of water (liquid or frozen).

NASA

Venus' white clouds
Venus: high-altitude clouds of sulfuric acid (!). The tan/orange is from the aforementioned haze.

NASA/JPL-Caltech

Mars' white clouds
Mars: a rare overcast sky. Martian clouds are made of water ice.

NASA/JPL-Caltech/MSSS

Putting it all together

The largest and most complex atmosphere in our solar system is Jupiter. But we know enough to start making some smart guesses about it!

QUIZ: looking at this picture, what can you say about Jupiter’s atmosphere? Answers below the image, so take a guess before scrolling 😉

A closeup of Jupiter's atmosphere
A closeup of Jupiter's atmosphere

NASA/JPL/University of Arizona

Here’s a comparison of how a basic guess – informed by our simplistic model – compares to scientific consensus.

Color Our guess Scientific consensus
Red Haze (couldn’t be dust; a liquid core makes that impossible) A haze of unknown composition
White Clouds, probably of ice because of coldness Clouds of ammonia ice
Slate (dark blue-gray) Small atmospheric molecules. But potentially a chemically odd haze, if something absorbed the visible spectrum pretty strongly? Hydrogen and helium – i.e. small gaseous molecules that scatter blue/violet

We didn’t do too bad, huh? A few key ideas explain a lot of sky color!

I’ll wrap up by connecting what we’ve covered to the larger picture of scattering.

Scattering: the bigger picture

Scientists have official names for the three types of scattering we’ve talked about. I’d be remiss not to at least mention them:

  • Rayleigh scattering: when the wavelength of light is much larger than the particle (e.g. visible light and tiny gas molecules)
  • Mie scattering: when the wavelength of light is the same order of magnitude as the particle (e.g. visible light and dust/haze)
  • Geometric scattering: when the wavelength of light is much smaller than the particle (e.g. visible light and droplets or ice crystals)

And yes, somewhat strangely, it’s not the absolute particle size that determines how it scatters light. It’s the relative size of the particle to the wavelength of light.

This table implies that if you take a particle and shine longer and longer wavelength light on it, it’ll go from one domain to the next. And that’s true!

The full picture looks a bit like this:

A chart of particle radius vs photon wavelength, showing Rayleigh, Mie, and geometric scattering
The variable x denotes the ratio of particle radius to photon wavelength. Dotted lines represent single x values.

This has some exciting implications. Say you have a thick smoke, opaque to the naked eye. Why not just look at the infrared range instead? If you use a long enough wavelength, smoke particles will be in the Rayleigh domain – where, of course, shorter wavelengths scatter much more than longer. So if we use a suitably long wavelength of infrared… the opaque becomes transparent.

That’s what firefighters do, anyhow!

Smoke particles are in the Mie domain for visual light. Thick smoke can absorb enough light to become opaque. But in the infrared range, it’s the Rayleigh domain. There, long wavelengths mean less scattering. Less scattering means more transparency. And thus, infrared can see through smoke.

I’m getting off-topic. I can’t help it. So let’s call it here. As you can see, what we’ve covered above is but a tiny droplet in a vast cloud.

But at least you know why the sky’s blue.

Further Resources

  • NASA’s sunset simulator. You know who really wants to know what color the sky is on other planets? NASA. They’ve built an incredibly powerful app for modeling atmospheres and radiation, and here they use it to crank out a few beautiful visuals of our solar system’s best sunsets.
  • Blue Moons and Martian Sunsets. The mechanics of Mars’s blue sunsets are still somewhat debated. The authors of this article make a convincing model based on the assumptions I worked with above.

Thank you to Dr. Patrick Irwin, Dr. Craig Bohren, and Matt Favero for corrections and feedback. LLMs were consulted in the research of this article, but any hallucinations are my own. I welcome further feedback.


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Comments

  • By staplung 2026-02-0917:296 reply

    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… """

    • By SAI_Peregrinus 2026-02-0919:442 reply

      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 "青" or some other word, the questions around qualia & what it means to perceive color, etc.

      • By __MatrixMan__ 2026-02-0923:473 reply

        There are differences in receptor behavior across species, but they are understandably clustered around the parts of the spectrum in which sol is most luminous. An earth-like planet orbiting a different star would likely have evolved photoreceptor arrangements which match that star instead. So after scratching the biology itch we'll probably need to talk about fusion byproducts in sol-like stars.

        • By kgwgk 2026-02-103:592 reply

          > they are understandably clustered around the parts of the spectrum in which sol [sun] is most luminous

          That would be understandable but it’s not what’s going on: http://hyperphysics.phy-astr.gsu.edu/hbase/Chemical/watabs.h...

          • By __MatrixMan__ 2026-02-1023:50

            I didn't know that about water, thanks.

          • By tim333 2026-02-109:26

            Ah - so I guess that's why snakes have pit sensors for infrared.

        • By hwillis 2026-02-1017:04

          > An earth-like planet orbiting a different star would likely have evolved photoreceptor arrangements which match that star instead.

          No, not really- the limitation is chemical, not evolutionarily-driven. Earth is very well lit in infrared, but it's very difficult to make a chemical that is biologically useful for seeing infrared because the wavelengths are just too long. Its very challenging to do more than the most primitive kinds of sensing in infrared. If our sun was much dimmer, we would probably be blind, but if not our eyes would still not see in far infrared. Same goes for ultraviolet- the energy is too high and molecular bonds are too weak. Seeing in visible light is a reversible reaction, but ultraviolet wouldn't be.

          What you're saying is true of ocean animals, especially in the deep sea. They don't see red very well or at all, but the evolutionary pressure against seeing red is not terribly high except very deep where food is very limited.

          There also is evolutionary pressure on our vision, but it has nothing to do with the sun. We're twice as sensitive to green since it is so common and important, but green comes from photosynthesis and not from the color of the sun. In a way, we are most sensitive to the least important color of light- the color that is not absorbed by plants. The wasted, useless byproduct of sunlight is what lets us identify food.

          Plus, we actually basically only see in blue and green. The overlap between rods and red/green cones is huge. "red" and "green" as we perceive them are mostly fabrications of our neural circuits- if we were seeing them how our photoreceptors actually receive light, all shades of green/red would be very strongly mixed together. All shades of red would look significantly green except for the very farthest reds, which would look very dark because of low sensitivity.

        • By jll29 2026-02-1013:23

          dogs see violet better, so "normally" our sky would be blue to them. But because their eyes have only two types of color receptor, they see violet as blue, and our sky is also blue to them.

          Same outcome, but for a different reason!

      • By reactordev 2026-02-0921:103 reply

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

        • By daedrdev 2026-02-100:141 reply

          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.sciencedirect.com/science/article/pii/S004269890...

          • By reactordev 2026-02-101:363 reply

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

            • By jaggederest 2026-02-102:221 reply

              We already have mutations, generally in women, for tetrachromaticism, who usually have male relatives with severe or moderate color blindness, in which the X chromosome encodes a different green cone. So they end up seeing red, strange-green, green, and blue, where strange-green is somewhere closer to red than green.

              Only a few on record but they tend to have absolutely insane color matching and color perception. One of note worked in the fashion industry and could match fabrics perfectly even in varying lighting (e.g. working under fluorescent but able to match colors that would stay matched in halogen/stage lighting)

              • By reactordev 2026-02-103:062 reply

                I have that already ;) it actually looks like muddy puke green than green. However, green stop lights look more “white” than green.

                Some reds look like brown. I hate reds. I’m not sure about the Pantone-like color matching but I definitely see different colors than most people. To the point where my flight license is restricted.

                Dichromatic but not trichromatic.

                • By jaggederest 2026-02-125:06

                  Not sure if you'll see this but you should check color perception with any female relatives, they're much more likely than average to be tetrachromats!

                • By codesnik 2026-02-106:191 reply

                  how does dichromatism restricts flight license? no instrumental flights? no night flights? something about perceiving warning lights on some panels?

            • By int_19h 2026-02-102:192 reply

              There's some evidence that tetrachromacy already exists in a few humans. If so we have the gene already. But why would it spread?

              • By lesostep 2026-02-108:162 reply

                fringe theory just for a bit of fun: since screen use 3 colors diodes, maybe people with tetrachromacy would be less addicted to screens, making them both more grounded in real life and marginally more successful, leading to them having more children?

                I have no idea how to test it. But in my heart I know that screens with RG, GB or RB color models would suck enough that any screen addiction would be cured instantly.

                • By reactordev 2026-02-109:101 reply

                  I wouldn’t be so sure, for a decade all we had was G and we used more and more of it until we died of dysentery outside Eagle River.

                  • By fragmede 2026-02-1012:171 reply

                    You were supposed to ford the river!

                    • By reactordev 2026-02-1014:54

                      You know our supplies were:

                      1 axle.

                      1 wheel.

                      1 bundle.

                      100 boxes of ammo.

                      10,000lbs of bear meat.

                      2lbs of squirrel meat.

                      We sank like a rock.

                • By tim333 2026-02-109:17

                  They need special screens with four colors and the internet updated to make it more interesting for the tetrachromatic.

              • By daedrdev 2026-02-1023:58

                this is true of many human mutations with the development of medical care, its not like we face evolutionary pressure for many things

            • By mr_toad 2026-02-1013:11

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

              There’s a Greg Egan short story (I think it’s ‘Seventh Sight’) where a bunch of formerly blind kids with cybernetic eyes hack the receptors to respond to wavelengths other than the traditional RGB. So perhaps it wont take millions of years.

        • By mncharity 2026-02-0923:061 reply

          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.

          • By reactordev 2026-02-101:382 reply

            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.

            • By AlotOfReading 2026-02-102:151 reply

              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.

              • By reactordev 2026-02-103:17

                This occurs in other animals as well.

            • By mncharity 2026-02-1112:25

              Imagine a chromaticity diagram, but on a perceptual color space where long-range euclidean distance at least attempts to describe the magnitude of perceived difference (rather than the usual model artifacts) - so round-ish. Then decreasing perceived difference between red and green shows up as a smush to oval.

        • By goatlover 2026-02-101:571 reply

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

          • By reactordev 2026-02-103:19

            You know that scene with the Nexus ribbon? Probably a huge version of that. But it depends on what timeframe we’re talking. Visor Geordi or Eye Optics Geordi?

    • By ecshafer 2026-02-0918:415 reply

      "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.

      • By leeoniya 2026-02-0919:152 reply

        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

        • By SAI_Peregrinus 2026-02-0919:592 reply

          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.

          • By dmd 2026-02-0920:26

            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".

          • By leeoniya 2026-02-0920:561 reply

            the good ones would usually follow up with, "how much detail do you _really_ want ;D"

            • By pas 2026-02-1010:37

              I always wanted to talk about our lord and savior (BGP) but so far no one took the bait!

        • By mgemard 2026-02-1012:29

          There is a chapter on why the sky is blue in The Feynman Lectures : https://www.feynmanlectures.caltech.edu/I_32.html

      • By ASalazarMX 2026-02-0923:12

        A great response is "What exactly do you want to know?", so we don't end up like Cliff giving answer after answer. In his case it was a great test question, but such a vague question is a horrible communication tactic if abused.

      • By noduerme 2026-02-104:49

        Having two older brothers who are famous trial lawyers, I can attest that it's both an effective line of questioning and a deeply infuriating one. What I learned is that up to a certain point, it's feigned ignorance probing whether one knows a principle behind a stated principle. Beyond that point, though, you can basically make shit up and they won't know the difference. Come to think of it, this is also the sleight-of-hand pulled by LLMs when you ask them for more and more detailed answers. The trick is knowing when your interrogator no longer knows the answer.

        [edit] Also, in my family, you'd ask Dad these questions. And if he didn't know the answer, he'd pull out the Britannica, and have you look it up, then go over it with you until he understood it well enough to explain it. "No short answers" was his motto. (He was also a trial lawyer). Most people are just not equipped to handle cross-examination, and it's scary for them... but the primary reason is that they never learned to admit when they don't know the answer.to a question, and that admitting you don't know is not a failing, but actually a strength, especially if it impels your curiosity to go find the answer.

      • By HPsquared 2026-02-0922:06

        It's reminds me of that scene from Fargo: "He was kinda funny lookin'" ... "Could ya be any more specific?"

    • By Ferret7446 2026-02-1123:46

      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".

    • By jstummbillig 2026-02-0919:5110 reply

      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.

      • By brabel 2026-02-0919:574 reply

        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.

        • By int_19h 2026-02-104:16

          I just did a crash course on lingustics by reading through a bunch of highly specialized articles.

          30 years ago, just finding those articles would require spending many hours in the library (and that's if I'm lucky and the library has them).

          It's definitely not just cat videos.

        • By mncharity 2026-02-0923:151 reply

          I saw a Microsoft talk decades back, that was a dispirited "the people of India could be buying educational materials and... but no, all the money is in ringtones". For some kinds of business perspective, ok I guess. But for others, and for civilizational change, what's going on in the tail can matter a lot. Does China become a US engineering/science peer in early 21st C absent an internet/WWW?

          • By eru 2026-02-1010:061 reply

            Well, the thing is that the educational materials are largely free. That's why the people of India don't need to buy them.

            Isn't that a better world than one where the ringtones were free?

            • By mncharity 2026-02-1112:481 reply

              Ah, perhaps I should have said something like "educational materials, and apps, and other useful things" (disapproving judgement in the original).

              > Well, the thing is that the educational materials are largely free.

              A triumph and fruition of these last decades of massive effort. Now we just need to deal with their quality (with commercial as bad as free). AI may help, by reducing barriers to content creation - you might for example, now more easily author an intro astronomy textbook, one that doesn't reinforce top-30 common misconceptions, something the most used (US; commercial) texts still don't manage.

              • By fivestones 2026-02-1114:331 reply

                I’m pretty curious. What are those too 30 misconceptions in US commercial astronomy texts? Is there a list somewhere? Or can you name some?

                • By mncharity 2026-02-1123:501 reply

                  Sigh. One impact of AI will hopefully be more readily available systemic survey papers. [1] might-or-not be a good place to start... but it's paywalled (by the National Science Teacher Association no less), and I don't quickly see preprints/scihub/etc. Here's an old unordered list for browsing[2], and a more recent one[3]. Trumper did a series of papers asking the same few questions of various populations, to give a feel for numbers - like half not knowing day-night cause. Most lists are on subsets of astronomy, and most info on frequency on short lists. So... it's a mess. As are textbook reviews. Key phrases are "astronomy education research" and "misconceptions".

                  The one bit I explored was 'what color is the Sun (the ball)'. Asking first-tier astronomy graduate students became a hobby, as most get it wrong (except... for those who had taken a graduate seminar covering common misconceptions in astronomy education). So I libgen'ed the 10-ish most used intro astronomy textbooks in US according to some list. IIRC, it broke down roughly into thirds of: correct (white); didn't explicitly say but given surrounding photos, or "yellow" (as classification without clarification), there's no way students won't be misled; and explicitly incorrect (yellow). Hmm, bulk evaluation of textbooks against some criteria is another thing multi-modal models could help with.

                  (A musing aside re AI for systemic reviews. Creating one is a structured process. They have been very manpower intensive, so they aren't refreshed as often as is desired, nor consistently available. And at least in medicine ("X should be done in condition Y"), there's a potential for impact. I imagine close reads of papers isn't quite there yet. But maybe a human-AI hybrid process?)

                  [1] https://www.per-central.org/items/detail.cfm?ID=14009 [2] https://web.archive.org/web/20070209033543/http://www.physic... [3] appendix A of https://digitalcommons.library.umaine.edu/etd/2200/ [4] https://www.oranim.ac.il/sites/heb/SiteCollectionImages/pers...

                  • By mncharity 2026-02-1312:51

                    s/systemic/systematic/g - oops.

                    > Systematic reviews are rigorous, transparent, and reproducible research studies that synthesize all existing evidence on a specific topic to answer a focused question and minimize bias. Unlike narrative reviews, they use predefined eligibility criteria, comprehensive searching, and critical appraisal to evaluate primary literature, often employing meta-analysis for quantitative results. [goog ai overview, edited]

        • By reactordev 2026-02-0921:11

          We got more than that. We got 24/7 surveillance.

        • By 6stringmerc 2026-02-109:18

          I grew up with Mr Rogers

          Gen Z grew up with Mr Beast

          We are proper doomed mate.

      • By robocat 2026-02-101:35

        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.

      • By lamontcg 2026-02-103:221 reply

        Sometime around 1992, I wrote a college essay on how the Internet was going to wipe out ignorance and enable true democracy...

        • By fransje26 2026-02-109:22

          Ah, crickets! Just got the two nouns in the wrong order..

      • By xenadu02 2026-02-131:06

        > who will have all their questions answered, correctly and in the way they can best understand

        Highly unlikely as the feedback cycle used to train LLMs will choke off all future learning.

        In other words if AI bots consume and regurgitate everything you publish on the internet what is the incentive to publish anything? No one will read it except the bots. The training datasets will either become stale (no longer learning anything new because nothing new and useful is published) or actively poisoned (because only bad actors will bother to publish).

        And the generation constantly fed mostly correct information by AI will implicitly trust it further making poisoning of the models a high-value target.

        Very few people will be left who understand how to think and have the motivation to do so. Even fewer will have the motivation and the means to publish to others.

      • By decimalenough 2026-02-0922:59

        I presume you're referring to LLMs here, but if so, your presumption that their questions will be answered "correctly" seems a bit optimistic.

      • By mncharity 2026-02-0923:27

        Does anyone have experience of early-childhood "Why?"-phase meets speech-enabled LLMs?

        Startup wise, there's old work on conversational agents for toddlers, language acquisition, etc. But pre‑literate developmental pedagogy, patient, adaptive, endlessly repetitive, responsive, fun... seems a potential fit for LLMs, and not much explored? Explain It Like I'm 2-4. Hmm, there's a 3-12 "Curio" Grok plushie.

      • By kakacik 2026-02-0921:22

        ... 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).

      • By ryanmcbride 2026-02-0920:24

        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.

      • By 6stringmerc 2026-02-109:17

        Hard truths are not desirable and I pity and envy your naitivity.

      • By Starlevel004 2026-02-0922:00

        When is that going to be?

    • By SwtCyber 2026-02-1011:33

      What I love is that the question is child-simple but bottomless

    • By hackeraccount 2026-02-1014:42

      I remember reading this - first thing I thought of too when I saw the headline.

  • By munificent 2026-02-0918:066 reply

    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.

    • By kazinator 2026-02-0919:04

      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?

    • By erikdkennedy 2026-02-0918:201 reply

      TIL!

      Debates whether to update the sidenote with an explainer on ambitransitive and labile verbs

      • By thombat 2026-02-1010:37

        Please do! It will fit the spirit of your splendid post, unpacking the complexity of a thing we take for granted (at least as native English speakers)

    • By srean 2026-02-0919:164 reply

      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' ?

      • By onestay42 2026-02-0919:451 reply

        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

        • By srean 2026-02-0919:55

          '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.

      • By munificent 2026-02-101:251 reply

        Interesting. This is indeed a funny gap in the language.

        "Show" work for any sort of visual thing you might want to present to someone. It's a bitransitive verb: it takes both a direct and indirect object in addition to the subject:

            "Bill showed Marsha her new car."
     ^^^^        ^^^^^^ ^^^^^^^^^^^ 
     Subject     D.Obj  Indirect Obj.
        For an auditory thing, our common words seem to subdivide it based on the sound source: "tell" for presenting speech to someone, "play" for presenting something musical:

            "Amy told Fred a story."
    "Bill played Fred a song."
        "Play" has grown to encompass recorded audio, so is probably the closest thing to an auditory equivalent to "show".

        There is also "audition" which can be used transitively, but I don't think it works bitransitively. You can say "I auditioned a bunch of saxophone recordings.", but you can't audition something to someone.

        • By srean 2026-02-1011:26

          Languages are so interesting, although I have zero talent in acquiring them. I don't care much for speaking them, pronouncing them right, but I do wish I could read some of the literature in their original language.

      • By msl 2026-02-109:211 reply

        In Finnish you might use "kuunteluttaa". You start with "kuunnella", "to listen" and inflect it in the way that turn a verb into "make someone verb". This particular example is a little unusual, but the same thing is commonly used with e.g. "taste". It works with all kinds of verbs, so it comes handy when you want your car serviced or your house painted.

        • By srean 2026-02-1011:27

          Thanks for showing :)

      • By smlavine 2026-02-0919:381 reply

        "tell"?

        • By srean 2026-02-0919:513 reply

          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.

          • By 1718627440 2026-02-109:22

            As the sibling points out show works for audio as well. Also vision is directed while audio is not. You need to look at some thing specifically in order to see it, you do not need to turn your head, to listen, the sound needs just to be there. You might need to alter your perception filter for both.

          • By thaumasiotes 2026-02-101:431 reply

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

            • By srean 2026-02-1011:23

              I see (pun intended)

          • By ccozan 2026-02-0921:401 reply

            play?

            I played him the faint sound.

            • By srean 2026-02-1011:22

              Yes that will indeed work in a few cases.

    • By orlp 2026-02-108:10

      In modern usage (e.g. in gaming communities) "carries" has become not only ambitransitive but also a noun.

      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.

    • By tsoukase 2026-02-0920:202 reply

      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.

      • By GuinansEyebrows 2026-02-0921:23

        "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.

      • By 1718627440 2026-02-109:26

        That ambiguity results from the elimination of cases, other languages still have them (and I perceive English to have as well, I just treat them all as homonym). You wouldn't say that foo(a,b) has ambiguity, because foo(NULL, &b) and foo(&a, NULL) both exist.

    • By suzzer99 2026-02-0919:111 reply

      Now do clam steamers and shrimp fried rice.

      • By munificent 2026-02-103:012 reply

        I'm familiar with "steamer clams", but not "clam steamers".

        In "shrimp fried rice", "shrimp" is a noun adjunct [1], which is when you use a noun as an adjective.

        The charming ambiguity comes from it being unclear whether "shrimp" is an adjunct noun modifying "fried rice" ("shrimp fried-rice") or modifying the past participle verb "fried" ("shrimp-fried rice").

        [1] https://en.wikipedia.org/wiki/Noun_adjunct

        [2] https://en.wikipedia.org/wiki/Headline#Headlinese

        • By pierrec 2026-02-104:281 reply

          I thought the charming ambiguity came from "fried" either acting as an adjective or as a verb. These aren't just any shrimp, they're chef shrimp, and they've prepared some delicious fried rice for us. Isn't that incredible? Shrimp fried rice.

          • By munificent 2026-02-1015:57

            Right. It's a noun phrase either way. The question is whether it is rice that were fried by shrimp ("shrimp-fried rice") or fried rice containing shrimp ("shrimp fried-rice").

        • By suzzer99 2026-02-121:34

          Yeah, they're usually just called "steamers". I put clam in front of them to disambiguate. But it's always bugged me. They're not steaming anything! They're getting steamed.

  • By KellyCriterion 2026-02-0916:514 reply

    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

    • By Sharlin 2026-02-0917:281 reply

      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.

      • By adrian_b 2026-02-0918:181 reply

        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.

    • By wasmperson 2026-02-101:53

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

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

    • By jjtheblunt 2026-02-0917:521 reply

      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...

      • By amelius 2026-02-0920:301 reply

        I'm curious how they were able to patent a technique invented by nature millions of years ago.

        • By jjtheblunt 2026-02-0921:021 reply

          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).

          • By amelius 2026-02-0921:121 reply

            I see, but those MEMs mirrors were already invented.

            • By moron4hire 2026-02-0921:541 reply

              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.

              • By amelius 2026-02-0922:581 reply

                We're talking about a millions year old invention here.

                • By Dylan16807 2026-02-100:28

                  As far as the patent system is concerned, 20 years and a million years are the same thing. If you combine some million year old things in a new way, you can get a patent.

    • By __MatrixMan__ 2026-02-0923:53

      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.

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