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

141–150 of 279 posts

Re: Why is the sky blue?

#141

Post by daedrdev »

reactordev wrote: post #99
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…

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

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...

Re: Why is the sky blue?

#143

Post by kazinator »

> 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.

This is also why posters in a window turn blue. The warm-colored organic pigments that produce the yellows and reds do that because they absorb blue light and UV. And that light has the energy to knock apart their bonds and break them down. The dyes that absorb the lower energy waves, passing through blue, last longer resulting in bluing.

Re: Why is the sky blue?

#144

Post by Dylan16807 »

amelius wrote: post #121
moron4hire wrote: post #109

Earlier quoted context omitted.

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.

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

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.

Re: Why is the sky blue?

#145

Post by kazinator »

> 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.

Nope! Purple is not violet! It a color that the eye perceives when stimulated by both blue and red wavelengths at the same time; there is no wavelength that produces purple by itself.

Re: Why is the sky blue?

#146

Post by jabl »

signa11 wrote: post #37

didn’t cv raman prove just that via his raman-effect for which he got the noble prize ?

Kind of, but not really.

Rayleigh scattering is elastic (only the direction changes), whereas Raman scattering is inelastic (energy, that is color changes in addition to direction) scattering.

Re: Why is the sky blue?

#147

Post by mncharity »

"To whom have I given blue from my sunbeam?!?" might be another fun question. I explored it as a potential interactive, to see, geographically, where your direct sunlight is donating sky blue-ification. Especially around sunset - IIRC, think a 100 km neon tube, at 7ish km altitude, near-end 150 km up range, with a 15-ish km wide ground footprint with 3/4-ish of the ground-impinging light, and the rest of a 100 km wide path with the 1/4-ish.

Re: Why is the sky blue?

#150

Post by munificent »

srean wrote: post #65
munificent wrote: post #41

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…

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' ?

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.

Post reply on HN