Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Why is the sky blue?

explainers.blog

Post reply on HN
Print view View original

231–240 of 279 posts

Re: Why is the sky blue?

#231

Post by adornKey »

SwtCyber wrote: post #225
thoughtlede wrote: post #103

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, t…

"Air is blue" works surprisingly well as a first approximation, in the same way "the ocean is blue" works until someone asks why

I think the color of the ocean is an even more interesting subject than the color of the sky. There is even more interesting physics involved.

Re: Why is the sky blue?

#232

Post by fragmede »

reactordev wrote: post #195
lesostep wrote: post #189

Earlier quoted context omitted.

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.

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.

You were supposed to ford the river!

Re: Why is the sky blue?

#233

Post by mgemard »

leeoniya wrote: post #64
ecshafer wrote: post #49

Earlier quoted context omitted.

"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…

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

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

Re: Why is the sky blue?

#234

Post by jll29 »

Although dogs can see violet better than humans, the sky appears blue to them like it does to us, not violet (despite violet being closer to the resonance frequency of N and O atoms).

That's because dogs only have two types of cones (color receptors) in their eyes, blue and yellow, not three as we do, so they see violet as blue.

Therefore, the sky is blue to us and to dogs, but for different reasons!

Re: Why is the sky blue?

#235

Post by mr_toad »

reactordev wrote: post #152
daedrdev wrote: post #141

Earlier quoted context omitted.

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

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

> 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.

Re: Why is the sky blue?

#236

Post by mrb »

1718627440 wrote: post #208
mrb wrote: post #115

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 perfectly colorless, the sky…

At least my mental model of color before I learned the details in physics and chemistry was that of a property of surfaces, so your explanation wouldn't have served me. I would have expected, that the light becomes blue as part of the transition from "empty space" into "air", not as part of the "flight" through the air.

"a property of surfaces"

You can conceptualize Rayleigh scattering exactly like you did so it doesn't conflict with my explanation: as light hits the "surface" of nitrogen and oxygen molecules, it "reflects" (scatters) blue wavelengths.

Re: Why is the sky blue?

#237

Post by jll29 »

__MatrixMan__ wrote: post #130
SAI_Peregrinus wrote: post #71

Earlier quoted context omitted.

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

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.

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!

Re: Why is the sky blue?

#238

Post by mr_toad »

adornKey wrote: post #231
SwtCyber wrote: post #225

Earlier quoted context omitted.

"Air is blue" works surprisingly well as a first approximation, in the same way "the ocean is blue" works until someone asks why

I think the color of the ocean is an even more interesting subject than the color of the sky. There is even more interesting physics involved.

And biology. The amount of plankton in the water can tint the color noticeably .

Re: Why is the sky blue?

#239

Post by 1718627440 »

mrb wrote: post #236
1718627440 wrote: post #208

Earlier quoted context omitted.

At least my mental model of color before I learned the details in physics and chemistry was that of a property of surfaces, so your explanation wouldn't have served me. I would have expected, that the light becomes blue as part of the transition from "empty space" into "air", not as part of the "flight" through the air.

"a property of surfaces" You can conceptualize Rayleigh scattering exactly like you did so it doesn't conflict with my explanation: as light hits the "surface" of nitrogen and oxygen molecules, it "reflects" (scatters) blue wavelengths.

I was talking about the understanding of a child, which didn't learned physics and chemistry yet, so there are also no atoms. Of course now I know about them, but at the same time, what I used to call a "surface", simple doesn't exist anymore.

Re: Why is the sky blue?

#240

Post by adornKey »

mr_toad wrote: post #238
adornKey wrote: post #231

Earlier quoted context omitted.

I think the color of the ocean is an even more interesting subject than the color of the sky. There is even more interesting physics involved.

And biology. The amount of plankton in the water can tint the color noticeably .

Yes, to all the the scattering, the sky has, you have water and other material relevant for absorption in the path. In the end even the colour of the ground might matter. In the past some people said, that the sea is blue, because it's a reflection of the blue sky, but that covers only a part of the problem.
Post reply on HN