this post was submitted on 22 Aug 2026
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Science Memes

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[–] isleepinahammock@lemmy.blahaj.zone 125 points 1 week ago (4 children)

I liked a version of this (I believe) XKCD said once.

A perfectly valid response to the question, "why is the sky blue?" is simply, "because air is blue."

Yes, you can give a lot of explanation about refractive index and Rayleigh scattering. But all this does is provide details of how light interacts with air. And the same reason anything is the color that it is is due to the way it reflects, transmits, or absorbs light. You're citing real scientific principles, but you're ultimately just explaining why air is blue.

[–] bullsworth@pawb.social 73 points 1 week ago

It's a very good relevant XKCD.

The title text is more directly applicable: If you ask "why are leaves green?" the usual answer is "because they're full of chlorophyll, and chlorophyll is green," even though "why does chlorophyll scatter green light?" is a great question too.

[–] Redditmodstouchgrass@lemmy.zip 21 points 1 week ago (2 children)

"Don't breathe air, it has sharks in it! BLUE HAS SHARKS IN IT!" -The funny purple man

[–] prex@aussie.zone 5 points 1 week ago

First if all: don't name your kid brayden.

[–] isleepinahammock@lemmy.blahaj.zone 5 points 1 week ago (1 children)

“Don’t breathe air, it has sharks in it! BLUE HAS SHARKS IN IT

???

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[–] tetris11@feddit.uk 16 points 1 week ago* (last edited 1 week ago) (1 children)

But it's an incomplete answer.

"air is invisible at short distances, blue at longer distances, and takes on red green and orange at sunset" would be better

[–] isleepinahammock@lemmy.blahaj.zone 26 points 1 week ago (7 children)

The same is true for all colors. Tell me the color of a single atom.

Yes, air can be colors other than blue at unusual light conditions, like sunset. But the same is true for any material.

You're stuck on the urge to explain. You call "the air is blue" incomplete. But all answers are incomplete. When someone asks what color an object is, they mean under ordinary distances and conditions. Air is blue even in an ordinary room. It just takes miles worth of air for its slight blue color to be noticeable.

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[–] brown567@sh.itjust.works 9 points 1 week ago (1 children)

Better question: "Why is the sky usually blue but sometimes red?"

Talking specifically about sunsets, not apocalyptic wildfire smoke

[–] SLVRDRGN@lemmy.world 6 points 1 week ago

Incidentally it's the same reason between a sunset and smoke - more scattering.

[–] aeronmelon@lemmy.world 65 points 1 week ago (2 children)

“Incandescent rage” is one of those phrases I have pocketed for a future conversation.

[–] rethnor@lemmy.zip 36 points 1 week ago (4 children)

Except the sun isn't yellow, it's white with a slight bias towards green.

Want to check, put something white outside, it looks white, not yellow.

[–] merc@sh.itjust.works 46 points 1 week ago (4 children)

The reason the sun appears to be yellow is the same reason that the sky appears to be blue.

Blue light is scattered more by the air in the atmosphere than other wavelengths. Remove blue from white light and you get yellow. So the light coming from the sun that isn't scattered and dispersed through the sky (making the sky look blue) is yellow.

[–] rethnor@lemmy.zip 1 points 6 days ago (1 children)

Still, the sun is white. Sun light is white.

Are you saying the blue light is removed from the spectrum when it's passes through the atmosphere? I assume you aren't since you said scattered, but also imply the sun is yellow because blue is removed.

If we're talking about sun light during sunrise or sunset then yes it gets red at more extreme angles. But the sun isn't that color all day.

[–] merc@sh.itjust.works 0 points 6 days ago

Still, the sun is white. Sun light is white.

That's why I said "appears to be yellow".

Are you saying the blue light is removed from the spectrum when it’s passes through the atmosphere?

The light from the sun is made up of a whole variety of wavelengths. You can see that when there's a rainbow and every wavelength from red to orange to yellow all the way to violet is represented. This light arrives in a continuous stream of individual photons.

When short wavelength photons (blue wavelengths down to violet wavelengths and below) hit the atmosphere, they're more likely to be scattered by air in the atmosphere. Because of that, they still hit the ground, but they're no longer coming from a direct line from the sun. That's why when you look up at the sky you see it as being blue, because photons that weren't originally heading toward you were scattered and come towards you from a random direction.

The longer wavelengths, from green on up aren't as likely to be scattered by the atmosphere, so they mostly come in a direct line from the sun to your eye.

As a result, if you look directly at the sun (which you generally shouldn't do) it will appear to be more yellow than it actually is. Astronauts above the atmosphere see the sun as appearing fully white. But, on the surface we see it as white minus all the blue that was scattered. The result is that the sun appears to be yellow when you're on the surface with the atmosphere scattering things.

At sunrise and sunset there's even more scattering. Now even larger particles are involved, and there's more atmosphere to shine through. The blue is removed, but so is a lot of the green and yellow, leaving only the red, which is the least likely to be scattered since it has the longest wavelengths.

So, at sunrise and sunset the sun can appear reddish. At noon it can appear yellowish. But, if you go above the atmosphere so the blue doesn't get scattered, you'll see that it's actually white.

[–] mirshafie@europe.pub 3 points 1 week ago

And here's the correct answer, boys and girls.

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[–] Allero@lemmy.today 8 points 1 week ago (1 children)

Neither water is blue

They take us for absolute fools

Maybe not the water you drink (chugs Gatorade frost)

That's why I never developed super powers.

[–] g0d0fm15ch13f@lemmy.world 3 points 1 week ago (1 children)

with a slight bias towards green

And it's my understanding THATS why plants are green

[–] brown567@sh.itjust.works 5 points 1 week ago (1 children)

Actually, leaves look green because they don't absorb green light (that's why grow bulbs are red & blue)

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[–] CareHare@sh.itjust.works 35 points 1 week ago (3 children)

Purple leaves are a thing.

[–] lemmyng@piefed.ca 75 points 1 week ago (2 children)

That's from plants that get their air mostly from the shade and sunsets, so obviously they'd be less yellow and more dark and red.

[–] CareHare@sh.itjust.works 51 points 1 week ago (1 children)

I know this is a joke, but to be fair: the scientific consensus (now) is that the purple pigmentation acts as a sort of sunscreen against too much sunlight.

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[–] MML@sh.itjust.works 6 points 1 week ago (2 children)

There's also an extremely tiny percent of plants that are entirely white, they don't get their energy through photosynthesis but instead a parasitic relationship of fungi and other plants.

[–] sneekee_snek_17@lemmy.world 6 points 1 week ago (2 children)

Mycoheterotrophs! Love them, such bizarre little plants

[–] MML@sh.itjust.works 4 points 1 week ago (1 children)

I was so disappointed when I learned how hard (I mean I haven't actually tried it) to culture them, but it makes sense given how they occur.

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[–] ech@lemmy.ca 14 points 1 week ago (1 children)

Whinging about a fact being wrong without providing a correction is worse than the one being wrong.

[–] gwl@lemmy.blahaj.zone 16 points 1 week ago (8 children)

The thing is it's kinda right, just lacking detail

[–] hirihit640@sh.itjust.works 4 points 1 week ago (7 children)

Cab you help explain it? I thought that the sky was blue because it reflects the ocean and because of rayleigh scattering, but do either of these affect the color of plants?

[–] ilinamorato@lemmy.world 9 points 1 week ago (1 children)

You've got it partially backwards. The sky is blue because of Rayleigh scattering, but it doesn't reflect the ocean; the ocean is blue because it reflects the sky.

Incidentally, I've heard it said (I think it was xkcd) that we use the term "Rayleigh scattering" because it sounds silly to say that the air is blue (via the mechanism of Rayleigh scattering); so maybe that's part of it?

[–] Ratio_Tile@lemmy.blahaj.zone 8 points 1 week ago (1 children)

The bit about the ocean being blue because it reflects the sky is unfortunately mostly wrong. Water is slightly more blue than ozone, so the more of it there is (big water in big ocean) the more blue it will look. The fact that it's also reflecting the blue sky adds to the color, but on a cloudy day the ocean is still blue.

[–] ilinamorato@lemmy.world 4 points 1 week ago

I'm about a kilometer from the ocean right now (I'm standing in front of the window through which I can see it), and it's a partly cloudy day. When the sky is clear (as it was five minutes ago), the ocean is a rich, saturated blue or even teal. When it's cloudy (as it is currently), I can see that it's a cool gray color. I might call it a very dark, desaturated cyan at most. So from my observation it has to be the opposite: the relative blueness of the ozone and the water must be the less dependent factor, and the color of the sky the more dependent one.

It's tricky, though. I guess I might be in a place with weird salinity or plankton or something.

[–] phonics@lemmy.world 4 points 1 week ago* (last edited 1 week ago) (2 children)

Plants are green because they absorb all other wavelengths of light. And bounce the green into your eye. In actual fact, color only exists in your brain as a way to understand the world around us. Our eyes are just sensors that detect light. And color is how we process it. We could have evolved into understanding it in different ways too, like smell. Therefore color doesnt even exist in the natural world. Green is just an illusion of our mind.

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[–] Digit@lemmy.today 10 points 1 week ago (2 children)
[–] Naz@sh.itjust.works 5 points 1 week ago

Blue waves fast Red waves slow

Easy as

[–] humorlessrepost@lemmy.world 3 points 1 week ago (1 children)
[–] Digit@lemmy.today 1 points 4 days ago
[–] AgentOrangesicle@lemmy.world 5 points 1 week ago (3 children)

I'm still not following. What part of "blue air" imparts chlorophyll with its color? I get the sun. I understand how light works (reflection, refraction, and scattering). I understand our perception of light on a neuological level (including post-processing) to an extent that most people haven't studied. Why "blue" air make green plant?

[–] Deme@sopuli.xyz 5 points 1 week ago (3 children)

My guess would be that plants optimize also for absorbing a significant amount of the light they receive from the blue sky, so they still get some when direct sunlight isn't available.

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[–] MonkderVierte@lemmy.zip 4 points 1 week ago* (last edited 1 week ago) (2 children)

Air is light blue because it filters out red, which is why chlorophyl has optimized for the mix of the remaining wavelengths yellow and blue, which is green. Color theory of additive blending.

(Our sun is slightly yellow, which is why the sky isn't cyan and why alot of tropical plants are darker green close to brown/red)

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[–] Sixseven@sh.itjust.works 4 points 1 week ago (3 children)

Mix blue and yellow paint and you end up with green paint.

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