Why is the Sky Blue

[@cloudstrife206]

I have just discovered this channel, it is fantastic, I’m totally hooked.

[@Key-wg6dn]

I KNOW

[@respekted]

That was the most thought out, effective and efficient presentation I've seen. So many concepts explained in 12 min about such a universal question. You sir, are a master prof of the KZbins. Thank you for this, and may your efforts continue to make us less science illiterate and more informed.

[@illinoisenergyprof6878]

Thank you!

[@mrfinesse]

Thanks Professor. The first time someone has given an easy to understand explanation. The Green Flash was a bonus.

[@toastrecon]

I've heard this explained so many times, and have never really been able to visualize it. This short video and the diagram make it so clear, I wonder if the other people who have explained it to me in the past really knew themselves.

[@leodikinis7390]

This is by far one of my favorite videos and my “go to” for quick education of friends and family. Having lived in the Caribbean I’ve heard much beach bar talk and wild explanations about the “green flash” at sunset. It’s wonderful to understand the process and to be able to explain it to others. As always, thank you for the excellent presentations and I am looking forward to future releases. I always figured that “42” was good for something.

[@Oheeeoh]

Thank you for sharing your wisdom with us professor.

[@mazelme]

4:30 "The answer to everything in the universe ". That was awesome. I'm still laughing. Thank you!

[@grimewl8257]

Now we just need the ultimate question

[@tb-cg6vd]

@@grimewl8257 I've got a computer the size of Earth for that one. Just have to get rid of those pesky mice.....!

[@vacheslavmanin2434]

Excellent teaching style

[@bobnovac3558]

Love this guy so fun to listen to. Notice he is so brilliant he writes backward for you to see. See Xe135 lecture

[@electrolytics]

Love this channel. Every video is interesting from start to finish. No fluff.

[@kaurkangur]

An amazing video explaining an interesting topic using understandable language.

[@BluesManPeich]

I can't get enough of the intro. Love the people screaming after the last kaboom.

[@joshuaevans4301]

This is the best explanation for this topic that I think I have ever seen. Bravo

[@Bonno460xvr]

Thanks. It’s exciting to learn new stuff.

[@asayake1]

42 - the answer to live, the universe, and everything.

[@dondo84svo]

Perfectly explained as always, thanks

[@tommypetraglia4688]

¡I've seen the Green Flash!, and captured it on film, anchored with tug and barge unit in Buzzards Bay Mass., Dec. 31, 1999, as we were directed to lay wherever we were for 12 hours for the possible potential of the Y2K bug. Happy New Year to One and All

[@Yes_it_is_JPB]

Greatest explanation ever.

[@randyhavener1851]

Wonderful Christmas Present! Thanks David!!!

[@jaymahaffey4133]

I enjoy your videos. I found you through a distracted curiosity in studying nuclear matters of all types but I like the other stuff too. My primary focus is on agricultural research (cotton entomologist/physiologist by training.) I teach a group of interns, college kids, school children and a wide variety of others each year and I always try to keep a couple of questions to make them think. This applies directly to one of the questions. My leading questions are: Why does the cotton plant have lint?? and Why are their so few blue objects in nature? I can't prove either (and usually refuse to answer in any absolute way) but it drives my students crazy and makes them think about it. Thanks for doing these.

[@icthulu]

I have a curious question for you, is chlorophyll green because that wavelength is the most abundant?

[@1906Farnsworth]

@@icthulu No. If Chlorophyll preferentially absorbed the green, it would appear pink or magenta, not green. It looks green because it absorbs the other colors. It seems to reject most of the energy available, based on that.

[@robertgoldman8064]

I new about the blue and red skies, but did learn , that a rainbow is about the 42° angle and the light that is scattered is up and not reflected back to you.

[@justjk-ing]

So glad he got a new pen after Mr. Sun.

[@respond_code3]

MIND BLOWN! I could listen to this guy all day! Actually just wanted to know if Gamma radiation only happens upon detonation of a nuclear bomb, or it's also in the fall out. I assume it's in the fallout as well which means those of us in FL are SOL. That wasn't covered in our 2 whole chapters in college on wmd/wme. Glad I stumbled across his videos.

[@mrlucasftw42]

Question - why does a white wall not act like a mirror? After all, white is a reflection of all visible wavelengths.

[@LHFX]

For the same reason a blue wall does not act like a mirror for blue light. A wall will reflect light in all directions and cannot act like a mirror, unless it's super super smooth at the nano-meter level... like a mirror.

[@crimsonhalo13]

You mean ... the green flash DOESN'T signal when a soul comes back to this world from the dead? This is either madness or brilliance!

[@miranda9691]

Incredible how we can spend decades in scholl and nobody tells you can see a green sun!

[@jonnyjetstreamer997]

Little Freudian slip there at 02:26? Love your videos!

[@Mandragara]

That pen is the loudest object in the universe

[@adamkendall997]

How exactly does a posi-trac on the rear end of a Plymouth work?... It just does.

[@blipco5]

Adam Kendall ...Not a joke. Watch this it's an excellent description. kzbin.info/www/bejne/r4qkqGpvaJ1pjas

[@erg0centric]

It doesn't work any more, Plymouth is dead.

[@blipco5]

erg0centric ...For something to be dead it once had to be alive.

[@johno9507]

That's easy, a Posi-trac uses pyrolytic carbon clutches to effectively lock the right & left axles together for positive straight line traction yet allows for a limited amount of slip & rotational speeds between the two axles during cornering...see so simple a baby could understand it. 👶

[@jermainerace4156]

"Positraction" was the trade name used by General Motors for the Limited Slip Differential installed in Chevrolet and GMC products. It could not normally have been installed in a Plymouth. Chrysler had an LSD however, and called theirs "Sure Grip". There are some noteworthy differences between the various LSDs from the various manufacturers, so your best bet is just to hit up wikipedia or an old technical manual if you want to know specifically about the one in any given car instead of trusting what anyone on YT says.

[@rjvtechnologies]

how photons do accelerate or slowdown when getting in contact with the prisms at the molecular level ? how contact is actually made? like in gravity, its assumed is there but no one can explain how it works only what does, is like describing what is possible by having a car but never describing what car is made of, etc

[@jnklee]

Thank you for using a new marker for the sun: the old one was hard to read!

[@phugoid]

Cool, so is it because there's no scattering on bodies such as the Moon and Mars (since they have no atmosphere) that their skies are always black?

[@paranoiia8]

Amazing... But did you explain that like that to the 5 years old you mention? 😅 But seriously. Why sky sometimes is purple or more orange? Does angle of earth change a little bit so it hit different wave length of light? But then how it's not visible everywhere and more often? Or its some external element that make it shift from red/orange?

[@illinoisenergyprof6878]

My two youngest grandchildren are 5, and are at my home today. The video was indeed too much for them. I swear I said the same thing to their parents when their parents were five! Don't know what happened....

[@TS-jm7jm]

@@illinoisenergyprof6878 communists softening the curriculum?, i am not american but i have seen parts of your curriculum and it is shocking how little is expected from your students; for example your first year or so of university at least back home is what we wouldve covered in highschool at 16-17 in maths that is, now whilst your education is good at the end of it and dare i say of quite a high standard; it is your basic education which appears sorely lacking.

[@georgemarek4193]

Why aren't there any stars in phtographs taken by our manned space missions?

[@birgirkarl]

Ah ha, I look forward to explaining this to my 5 year old tomorrow. She might probably kill me though!

[@realvanman1]

So... the sunset is not red because the longer wavelengths are bent around the Earth to a slightly greater degree? And the sky is not blue because of the oxygen?? Damn. I’ve had this wrong for decades!! A very good presentation!

[@ralanham76]

I love the markers. It's like audio Braille. 😁

[@Gameboygenius]

Here's today's most minor complaint: at 2:30 UV and IR ought to change places. If that's a graph of Planck's law, high energy (UV) should be on the steeper side of the graph.

[@illinoisenergyprof6878]

You are absolutely right. I blew it. (Of course, I did not have a legend, and it could be that I was plotting wavelength and not energy.....!)

[@MultiZirkon]

I have never seen the Green Flash after the sun has set. -- But I have seen it it several times above the sun just before all of the disc turns red. I have even seen the blue flash there, with binoculars (and welding glass).

[@kabubagachugu7729]

How to piss off a flat earther. 8:50 "lets make the world a little bit more rounder"

[@erg0centric]

Once when a thunderstorm cleared right at sunset the whole sky turned green, is this caused by the green flash?

[@cloudstrife206]

Is there any videos relating to the use of hydrogen as an alternative to hydrocarbons? If not would you consider making one? Thanks so much

[@erg0centric]

Have you tried 'hydrogen as fuel' in the search bar?

[@d0nutwaffle]

Cool refresh of some high school information, though an interesting though that didn't cross my mind at the time was that if you'd end up on some alien planet orbiting a sun simliar to ours, barring any extreme atmosphere situations,... then day and night wouldv'e looked pretty much the same as on earth. Not sure if comforting or creepy.

[@jeremythompson9319]

That's a great explanation of how light travels, but wouldn't it make more sense that the sky is blue because the planet earth is covered by this layer you may have heard of it, it's called the OZONE layer which has a pale blue tint in large quantities.

[@hypnoticm0nkey]

I love this man, even laymen's like me can keep up 😂😂😂

[@TheAngelOfDeath01]

Give this man the Nobel Science Price !

[@jeremydyar7566]

That doesn't exist

[@TheAngelOfDeath01]

@@jeremydyar7566 Yeah, it does, but it's split in three to distinguish the different segments of Science. The two other Nobel awards are Peace and Literature. But science is split in three: Physics, Chemistry, Physiology and/or Medicine. But yes, science very much exists.

[@johndoh1000]

But if red light doesn’t get as easily diffused through our atmosphere wouldn’t the sun have a red ring around it all throughout the day?

[@nobody1841]

Why are double rainbow's colors reversed?

[@Fox_McCloud]

I'm guessing this is also why plants are green, to take advantage of the peak amount of energy.

[@capttelush539]

Except they don’t absorb the green light, that’s why you can see it

[@Fox_McCloud]

@@capttelush539 Yeah, you're right. I didn't think that one through very well.

[@jermainerace4156]

@@capttelush539 They are green for the same reason some plants are red: blue and violet light is at a higher energy level than green or red, so it can get over the threshold needed for the photosynthesis process of green plants (there are others). Plants reflect the green light on purpose, since it would just make the plant hotter for no reason. Red light is relatively low energy, so I'm guessing they just ignore it unless they are extra sensitive to heat? I'm more of a chemist than a biologist though, so I'm not 100% sure my guess about the reflection is correct.

[@piotrfila3684]

I think I saw this video on the channel already. Is this a reupload?

[@AvindraGoolcharan]

They've been re-uploading videos, editing and such along the way kzbin.infoUgyqvTXcluI4fR9gfWN4AaABCQ

[@jeremymettler2844]

Yes it is, he's re-uploading some of his favorite videos that have fewer views, until he and I can get back into consistently producing new ones!

[@physjim]

then why is it not purple?

[@jermainerace4156]

I asked this same question.

[@davidwilkie9551]

"Drawing a long Bow" as explanation goes, we could say the observable universe is due to omnidirectional-dimensional modulation-scattering of time duration timing at the Temporal Superposition-point Singularity Holographic Image projection positioning. Same basic principles universally, is what we have to know.

[@jigitbigit3088]

Omg, could you somehow remove that squeaky sound when you writing on the glass?

[@niczanelli]

But if the blue light scatters 10 times more than red, wouldn't the violet light scatter even more? Why isn't the sky violet?

[@Eddie42023]

Probably because violet, like UV, is greatly absorbed by the atmosphere, and re-emitted at different wavelengths.

[@alfreds8766]

Ohhhh boy, at the end of the video I wanted to clap man!!!! 👏👏👏👏👏

[@MeaHeaR]

Why aré there No Green Stars ¿¿¿¿¿

[@tomballard9584]

Am I the only one who’s blood goes cold at the sound of that marker squeak?

[@erg0centric]

Yes

[@michaelkaliski7651]

That is nothing compared to the squeal of chalk on a blackboard. I guess you have to be pretty old to remember that.

[@Ericisnotachannel]

not as much as it being white and barely being able to read it.

[@illinoisenergyprof6878]

Stay tuned! We taped some more content and the new "light board" does not squeak. Amazing!

[@tsvetangeorgiev]

and I thought that I had this all figured out :)

[@NGC-gu6dz]

:) thank you. I never knew.

[@Eddie42023]

red light coming from the sun goes through the atmosphere, blue gets thrown all over the place. You only see red from the sun, blue comes from all over the place, so everywhere BUT where the sun is, is blue.

[@popcharlie]

If the maximum of the solar spectrum is green, then why are plants green? Plants look green because they reflect green light, while absorbing red and blue. Why haven't plants evolved to absorb green light preferentially? and instead reflect other colors? If the solar spectrum maxes at green, wouldn't pigments that absorb green light and feed those photons into the photosynthetic reactions provide the most energy to plants?

[@muradm7748]

Answer from reddit I was satisfied with: If our eyes had a near infrared receptor, plants would appear to be that color instead of green. Chlorophyll and other plant pigments absorb a great deal of the human-visible spectra. They reflect about 5% of the red and blue and about 10% of the green (but, as you noted, there's also a lot more green light coming in). So there's not really that much variance to need to explain, but part of it is that plant pigments have a major constraint in that they need to be capable of efficient photosynthesis -- pathways for red and blue light are the most efficient. Compare the reflectance of green vegetation in the visible range (0.4 - 0.7 on the graph) with their reflectance in the near infra red (0.7-1.0). They reflect about 70-80% (creating the red-edge, or visible cliff, which is useful for remote sensing of vegetation). If we could see NIR, that's the color plants would appear (really are). So the followup may be, why not use all of the visible light and be black? Plants can only use so much energy as it is -- they have other limitations like water and gas exchange. Also, they get hot. Kudzu leaves turn on their side during hot summer afternoons in the southeast US to avoid the sun.

[@jermainerace4156]

@@muradm7748 Some plants are black, but depending on where you are, that might create an overheating problem? EDIT: Oh sorry, you said that.

[@HughesEnterprises]

I used to work for some Scientologists. They tried convincing me the sky was blue because that’s what color oxygen/nitrogen is... They were weird. Truly believed they knew the answers to everything in the universe and they were doing me a great favor letting me know their privileged “scientific” knowledge.

[@snd28081]

Very interesting but i can't handle the squeak of the markers.

[@tofagakilifi9535]

Do you think the child is asking for the very valid answer you've given or why its not in their favorite or is in thier favorite colour? That's the real question.

[@cb8673]

To quote George Carlin, "The sky is blue because that's the name we gave that color."

[@jermainerace4156]

I mean, he's not wrong.

[@houmamkitet9555]

Hello professor, not sure if you are still answering questions but i had to get mine out there cause i am unable to use the google machine effectively enough to figure it out on my own, what is superheated steam and how exactly is it an issue for nuclear reactors (i have a slight undertsanding of the issue but i would still like an explanation), furthermore what are we doing to try and overcome that limitation (i read about using oil/fuel as a superheater(steam to super heated steam) while the nuclear reactor is turning the water into steam but i also heard about purely nuclear reactor attempts at solving the issue and i understood none of them. thanks in advance and i will be sure to ask the question again if you can't answer it right now (maybe consider holding a Q&A session for all your new students)

[@illinoisenergyprof6878]

Superheated steam is simply steam that is higher temperature than the point at which it turns to steam in the first place. It is useful in electricity-generating turbines because it can be cooled (ie, energy extracted) and still be steam. It does not have to change phase (ie go back to being a liquid) to be used in the thermodynamic cycle. Hope this helps!

[@houmamkitet9555]

@@illinoisenergyprof6878 thank you professor, this slightly helps in explaining why we want super heated instead of normal steam but i am still quite curious/confused about it's uses in nuclear energy as it seems that it's not quite compatible from what i read (couldn't even find a nuclear only superheated steam plant, all i found were half reliant on fossile, the only mention i found was of the pathfinder powerplant that was a test trial for nuclear only superheated steam plants. Please do excuse any punctuation/spelling mistakes as english is not my mother tongue and thinking in 2 languages is lightly difficult

[@illinoisenergyprof6878]

No problem. The making electricity part is the same whether you are burning coal or doing it with nuclear fission. Basically you are boiling water. Any time you boil water if you can keep it all at very high temperatures you will be more thermodynamically efficient. Now, if you have a Boiling Water Reactor, where the water in the core itself is a mixture of steam and water, then you have to worry about the ability to moderate neutrons. Basically, water will do so and any kind of steam will not. That is all figured in to the design (if it gets too hot -- you get all steam --- you get no moderation -- therefore you get no chain reaction and the reactor stops).

[@houmamkitet9555]

@@illinoisenergyprof6878 Thank you very much for your time and knowledge professor, i assume the "hybrid" reactors that i have looked take the normal steam from the nuclear part and super heat it using fossile fuel, the one thing i still don't understand is what are we doing to overcome the problem of needing fossile (from the nuclear only design i have seen for the pathfinder plant) i think the idea is to have two seperate chambers for heating the steamand for superheating it but how to heat each chamber is still beyond me.

[@johnviera3884]

My 5 year old only lasted 2 minutes into this video 😂

[@anothermatt618]

I understand everything but the fact that the sky would be blue and not purple if purple is in visible light range and would scatter the most. Thinking it must have something to do with the human eye having only red blue and green cones . Because the green flash also makes you think why wouldn't you see an orange then yellow then green flash as sun progressively sets. Thoughts?

[@illinoisenergyprof6878]

You should see each progressive flash, but it has to do with your first answer. We are more sensitive to seeing the colors in the middle of the spectra. You are right about why we don't have an indigo sky.

[@jermainerace4156]

@@illinoisenergyprof6878 AH, thank you.

[@Jemalacane0]

Rayleigh scattering.

[@JohnAdorjan]

1

[@leslawangelo]

2

[@andrewmcgee1351]

3

[@tncorgi92]

5

[@dkoz8321]

I want this professior to explain how human sex works. I never quite got it, and don't get it! I just don't get it.

[@123Dunebuggy]

Gonna find out when subscribed to you

[@T0m3kPL]

42!

[@paulaglet4255]

Starts off really weak, finishes strong at 9:59. Almost a great lecture. The unanswered question would be, wouldn't the sky be different colors between the two observers? If the sky can be a strong color at the two extremes, it should also be a strong green, not a brief, pinpoint flash of green.

[@RoosterG33rs]

boom roasted.

[@MeaHeaR]

é Power-Phull Orrrsé-Strâylêans

[@spudhead169]

So the Sun is actually a very very very light green colour? Wow!

[@schwenke069]

Got ya. Blue and green, especially neon favorite. Why ... oh God why ... do people want red cars? Please explain. Please ...

[@jlemieu1]

hard to read writing.

[@Defunct231324141]

Wow, I thought it was because we lived inside an eye of a blue eyed giant!

[@ryanjones7681]

Ahhhhhh, so its just red v blue. Halo was right...

[@TheLoobis]

8:00. I'm bored.

[@stevepasquarella823]

in 9th grade our HS biology teacher told us the reason our sky is blue is because billions of cows fart and release methane gas, which is blue. Dude was university educated and he was not pranking us.

[@jermainerace4156]

"C's" get degrees...it is pathetically easy to become a teacher. In my generation (graduating the late 90s) a lot of students didn't like the economic outlook for the private sector and were like "hey, I'll get a teaching degree as a back-up". So, if you have a crappy 40-ish y/o teacher right now, just know this may not have been their first choice of careers.

[@sweyouknow]

First!

[@rustyshackelford4613]

That's not true, God made everything.

[@erg0centric]

You do you, keep the faith.