Neil deGrasse Tyson Explains Why The Sky Is Blue

chut with mini new so here's a question that resonates with my I shall say razor-sharp acumen why is the sky blue that hasn't been answered since childhood you know what here's the problem I asked once and they were like Maya business and that was we might say I want to become an atmospheric scientist it is my business there you go that would have it a very [Laughter] spirit scientist so alright so if the answer is easy to understand it's just not simple first of all is the sky blue yes okay well at least we got that it doesn't look blue to you it's fine that's what we're about to talk about all right okay so here's a deal the explanation is actually simple it just takes a little while to explain okay that's all alright alright I have time alright so we have an atmosphere okay we all know this yes we did it it's composed primarily of nitrogen okay a 78% nitrogen that's 20 21% oxygen and a few percent other carbon dioxide this sort of thing mixed in there are particles of like pollen and dust and sand from sandstorms and pollution and smog and so particulates particulates particulates okay now light comes from the Sun mm-hmm white light people people say the Sun is yellow it's white right okay exactly you've seen the Sun in the middle of the day it's white it is why okay that's the proper color of the Sun in the middle of the day let's not get racism it don't have to be the proper cup why is everything Rachel into you all right so you may remember that white light is composed of colors right okay put this light prism that's how you get a rainbow right or your your educator you said prison but through a raindrop it spreads mounted to college and you get the colors of the rainbow Boise bib okay give them to me right red green blue yellow Roy igb Roy red orange green Roy yeah red orange yellow green blue and ultraviolet but Valley bid okay indigo violet thank you red red orange yellow green blue indigo okay the seven colors of the spectrum okay if you come the way our brain works and the sensors in your retina okay the rods the cones the other rods give you shades of light and intensity the cones a disentangle color okay okay and you have an RGB cones this week at RGB for I heard that in computers and computer screens and everything okay so you're you're you are chemically with the chemicals in your retina splitting that red light into combinations of red green and blue okay okay broad combinations of these three if you have more red than the others than what you look at it's going to look more red to you if you have more blue than the others gonna look blue now here's what happens white light comes down from the Sun the particles in the atmosphere some of them are about the same size as the wavelength of blue light sweet all right now if the if you have a particle and light and there's a particle is the same size that right it'll reflect that's right it'll did or scatter that's the proper word okay bounce scatter and so that light doesn't make it straight through its sins in every other direction oh so the light from the Sun is selectively has the blue moved on its way down to Earth's surface and the and the blue scatters into the air and you have a blue sky that's very romantic is beautiful now it's called Rayleigh scattering got him Rayleigh greatly we get it re yl aigh okay Lord Rayleigh you and Lord the Ray alright so so here's the thing as the Sun gets lower in the atmosphere right the path length of the light is much longer through the air okay so in other words so here's your atmosphere if you're directly above you're going through it like this thickness and should come down the thickness gets more right okay right well more atmosphere more scattering right the sky gets more blue okay so in the daytime it's quote sky blue that's actually a pale Braille it's a very pale as you go to Twilight that sucker gets deep yeah it gives deep blue and so much more blue gets taken out of the Sun I just love how violent deep blue it's deep and if you take that much blue the Sun I got no blue light left at all so what color is it going to turn kind of red kind of red gotta read got a red amber yeah okay that's why sunsets are red that's because so much blue was taken out right that is that's all it has left to give you is the side of the spectrum we have red orange yellow that's know sometimes you have a very bright sunset that's not quite deep red mark many particles therefore that sunset all right many particles sweet so that's so kind of a lighter cut like yes so so the sky wouldn't get as intensely blue when that happens it'll be similar to the sky blue you had earlier in the day so that's that's why we have a blue sky nice now it's also why you can't see stars in the daytime other than the Sun well it's not it's not oh you can't see stars they come because the Sun is out that's not why because the Sun is brighter than the star light that you would otherwise see no that's not why well see that's intuitive knows how you with intuitive but it's wrong the reason why you can't see stars in the daytime is because the scattered blue light has rendered our atmosphere aglow the answer is glowing blue light and that prevents you from seeing the Stars behind it if you took away the atmosphere you'd be able to look up and see the Sun will be there but then you like dark adjust over here and there's Fulton Scott full stars right over here over there over there all around oh man you know what what if we didn't need atmosphere I'd want to get rid of it okay so now this is what led to the operational definition of the edge of the atmosphere okay okay it's it's just it's kind of operational it is how high up in the air do you have to go before there aren't so many air molecules above you for the blue light to scatter and prevent you from seeing the night sky so it's really about the number of particles it's not against an hour the actual no it's just a density particle wherever that happens so we agree just by convention if you go up a hundred kilometers okay converted to get 62 miles hundred kilometers that's about where the atmosphere is thinned out so there's no longer scattering blue light it is no longer a glow and in broad daylight you can see stars in the nighttime sky so that's the operational definition of space the operational definition of space is 62 miles above our ground surface kirai surface where you can just see space basically because that Mikayla's is still a mystery there was not dense enough to scatter blue light and render it a glow to prevent you from seeing the night sky now I'm not comfortable with that opera I understand it okay I'm not comfortable now what's your problem with that because if the atmosphere were half is thick as it is whether that would be only be 30 31 31 miles that would be space well suppose we're a tenth is it then it would be three miles suppose we didn't have an atmosphere you'd be a space just standing here sitting here like this should that be called space that's I'm saying it's our definition of space is linked to how the circles answers of our atmosphere that Cottam except well no I see what you're saying now because I was about to say it kind of makes sense because you can't breathe in space but you can also cannot breathe at 35,000 feet that's why yes where you can breathe hard enough to breathe just on a mountaintop exact you've won a quarter mile on a mountaintop so now you said what was your operational definition of space be if it is not indeed this this particular in atmospheric link I've thank you take out the atmosphere either you're in orbit or you're going somewhere then you're in space so you're using oh god you are such a damn astro fatigue as the measure of what makes space and that would be true no matter what atmosphere we had gravity fit into this okay you talking about our atmosphere so you know how much atmosphere that is 62 miles that's high up I'll show you all right oh my god you had to break a globe to show us look at this is this is this is my god just hold this God holding like the globe that's right okay so I'm gonna show you here's the United States right and I just did some distances I know of New York to Boston yeah yeah that's 200 and 200 miles okay I have 220 month no 180 miles okay all right so so you take a third of that distance okay that's 60 okay make that go vertically up all right that's the edge of our atmosphere 3/8 of an inch up 3/8 of one inch off this is what makes it is is oh my God we're in danger so Earth's debt is not cold Earth's atmosphere is to earth as the skin of an apple is to an apple that's what I'm saying 'we don't have much air we are in danger that air is frail and fragile oh my god you're doing what to it and we're doing all kinds of nasty stuff to it that is unbelievable would you eat an apple that somebody just rubbed crap all over no oh that's insane also I didn't I didn't sorry I misspoke 3/8 of an inch up that's the altitude of the International Space Station orbiting oh my god so our atmosphere is actually yes so I'm just looking to hear there's New York and there's Boston so you're talking a couple of millimeters but you know millimeter above that's terrible that's the thickness of the air above which we say you entered space why are we not teaching this in school I mean seriously if you if if you ever want to have a true appreciation of just what a delicate balance we live in that is it right there correct ah correct it's chilling that's really cute of an Apple is to an Apple as the shellac on this globe is to the globe itself oh that is our atmosphere oh my god dude well there you have it we're all gonna die so that's why the sky is blue that's right that's why we should look after this little bit of air that we got here on the surface of the earth I'm with you and it's wide Neil thinks space should be defined by gravity not probably the circumstances of our hemisphere happen to be there you go you know I'm gonna agree with all three man yeah and not because you're my boss Startalk info bit as always people here [Applause] [Music]

Channel: StarTalk

Views: 1,215,446

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Keywords: startalk, star talk, startalk radio, neil degrasse tyson, neil tyson, science, space, astrophysics, astronomy, podcast, space podcast, science podcast, astronomy podcast, niel degrasse tyson, physics, Chuck Nice, sun, atmosphere, Rayleigh scattering, sunset, stars, gravity, white light, blue sky, science explainer

Id: UvmWxm3nR6E

Length: 13min 12sec (792 seconds)

Published: Tue Apr 28 2020