Blue Sky, Red Sunset: Light, Atmosphere & Scattering

0.000000    5.880000     Welcome to everyday explained your daily 20-minute dive into the fascinating house and wise of the world around you
5.880000    10.960000     I'm your host Chris, and I'm excited to help you discover something new. Let's get started
10.960000    13.760000     If you ever looked up at the you know the big beautiful blue sky and
13.760000    21.320000     Really wanted why it's that specific color. It's a question lots of people ask seem simple right even curious kids like
21.320000    25.360000     11-year-old Mariana AE from Tucson, Arizona
25.640000    32.480000     She sent us this exact question, and maybe your first thought is oh easy. The sky just reflects the blue oceans happens all the time people think that
32.480000    40.080000     Well get ready for a bit of a surprise. That's a common idea, but the real reason it's actually way more fascinating involves some well
40.080000    45.660000     Some pretty cool physics and chemistry. So today we're doing deep dive into this everyday marvel
45.660000    52.400000     We've gathered sources from universities NASA NOAA places like that. We want to unpack the science behind it all
52.400000    59.360000     You know why it's blue at noon why you get those amazing red sunsets even what skies look like on say Mars our mission
59.360000    64.000000     To give you the rundown. So you feel really glued in maybe even impress your friends next time around
64.000000    68.120000     Yeah, that's the plan because honestly, it's not just about a pretty view though
68.120000    74.560000     It definitely is pretty understanding why the sky is blue helps us get a handle on really basic stuff like light itself
74.560000    80.400000     What are atmospheres and made of even how we you know study the planet from way up in space will break down the the
80.400000    85.080000     Science parts make it clear easy to follow and hopefully kind of fun to okay?
85.080000    91.720000     So to really get into this where do we start is it about light itself exactly lights the key
91.720000    98.720000     Specifically light from the Sun now it looks white to us, right, but that white light is actually like a secret mix
98.720000    105.080000     It's got all the colors of the rainbow hiding inside it think of maybe an orchestra playing one big note sounds like one thing
105.080000    112.440000     But really it's all those different instruments playing together and we know this because well brilliant people figured it out like Isaac Newton way back
112.440000    119.500000     He used a prism that triangle piece of glass showed how white light splits into red orange yellow green blue indigo violet
119.500000    121.000000     R.O. Y.G.
121.000000    124.900000     B.I.V. maybe remember that. Oh, yeah, R.O. Y.G. B.I.V.A. from school
124.900000    130.160000     Exactly and you see it naturally too right in rainbows rain drops act like tiny prisms doing the same thing
130.160000    134.160000     But what's really crucial for our story is that light travels in waves waves
134.160000    145.360000     And here's the interesting part different colors have different wavelengths think of ocean waves red light has these long kind of lazy waves like big swells way
145.360000    151.400000     Offshore blue and violet light. They've got shorter much chopper your waves like nine little ripples on a pond and
151.400000    160.160000     These waves are tiny. I mean incredibly tiny. We measure them in nanometers nanometers. How small is that so small that thousands of them could fit
160.160000    166.560000     Across one human hair really really small scale stuff. Wow. Okay, so tiny ways different colors heading to Earth
166.560000    170.400000     But you said light isn't the whole story when you need the atmosphere right? What's that made of?
170.400000    173.360000     How does it fit in? Ah, yes the atmosphere couldn't do it without it
173.360000    175.360000     It's mostly made of super tiny particles
175.360000    179.480000     Molecules we call them mainly nitrogen and oxygen and when I say tiny
179.480000    180.720000     I mean really tiny
180.720000    182.720000     Remember how small those light waves are
182.720000    186.760000     Well, these molecules are hundreds of thousands of times smaller still
186.760000    190.360000     Yeah, like comparing of I don't know a football field to maybe a single grain of sand
190.360000    196.960000     It's that kind of difference and these little nitrogen and oxygen molecules. They're just zipping around constantly like
196.960000    203.240000     Billions of invisible tiny tennis balls bouncing everywhere. Okay, invisible tennis balls
203.240000    208.960000     I like that. So we've got light waves these tiny color waves coming in and they hit this soup of
208.960000    211.960000     Tiny bouncing tennis balls
211.960000    216.180000     What happens then when light meets a molecule? Right. That's the magic moment
216.520000    223.560000     When a light wave. Let's call it a light marble for fun actually hits one of these atmospheric molecules or tennis ball
223.560000    228.120000     Something interesting happens some light just bounces off reflects, but it's more than that
228.120000    232.520000     The molecule actually absorbs some energy from the light absorbs it
232.520000    236.440000     Yeah, for just an instant and then it re-amits that energy spits it back out
236.440000    241.540000     But in a totally random new direction that whole process. That's what scientists call scattering scattering
241.540000    246.480000     Okay, like the tennis ball eats the marble and spits it out the sideways kind of that's a good way to think about it
246.480000    252.800000     It gobbles it up and shoots it off randomly and someone actually figure this out right put a name to it. Yes indeed
252.800000    260.320000     Background 1870 there was a British physicist John William Stratt. You might know him better as Lord Rayley
260.320000    261.200000     Lord Rayley
261.200000    265.440000     He was the first one to really explain it properly and so the effect it got named after him
265.440000    271.200000     Rayleigh scattering Rayleigh scattering got it and the absolute key thing Rayleigh figured out is this
272.000000    279.840000     shorter wavelengths of light remember the blues and violets they get scattered way more effectively than the longer ones like reds and oranges
279.840000    287.280000     It's because their short choppy waves are just the right size to really interact with those tiny gas molecules
287.280000    292.800000     So the tiny waves bump into the tiny molecules more exactly. It's like those tennis balls are super picky
292.800000    297.200000     They really prefer grabbing and spitting out the blue light marbles much more than the red or orange ones
297.200000    301.600000     Okay, so if the blue light is getting scattered like crazy in all directions
302.560000    308.560000     What does that mean for us down here looking up? Well, it means that blue light gets spread all across the sky
308.560000    312.080000     So when you look up on a sunny day no matter where you look
312.080000    317.520000     You're seeing blue light that's been scattered bounced around and eventually ended up heading towards your eyes
317.520000    321.680000     And the other colors the reds and oranges. They mostly just keep going straight
321.680000    326.000000     They're longer laser waves don't interact as much with the tiny molecules
326.000000    328.000000     So they travel right through the atmosphere
328.640000    334.480000     More or less uninterrupted down to the ground. Okay, but hang on you said violet light hasn't even shorter wavelength than blue
334.480000    339.440000     So shouldn't the sky be violet that seems logical. Oh, that's a great question
339.440000    344.960000     You're totally right violet light is scattered even more than blue technically it should win. So why blue
344.960000    352.240000     Two main reasons first our eyes human eyes are just naturally more sensitive to blue light than they are to violet
352.240000    353.920000     We just see blue better
353.920000    360.080000     And second the Sun itself actually puts out a bit more energy in the blue part of the spectrum compared to the violet part
360.080000    365.840000     So there's more blue light starting the journey anyway. Oh, okay. So a combination of more blue light from the Sun
365.840000    368.880000     And our eyes being better at seeing blue
368.880000    375.840000     Blue winds blue winds the sky color popularity contest. Yeah, that's really cool. How our own biology plays a role
375.840000    378.080000     Okay, so the sky is blue. Yeah
378.080000    383.440000     But sometimes near the horizon it looks kind of washed out
384.000000    389.920000     Pailer almost whitish. Why is that? Yeah good observation that ties right back into Rayleigh scattering
389.920000    395.440000     When you look towards the horizon you're looking through a much thicker slice of the atmosphere right
395.440000    400.320000     The light has traveled a longer distance through the air to get to you. Okay. Yeah more air
400.320000    405.920000     So that blue light as it travels that longer path gets scattered again and again and again
405.920000    410.720000     It bounces around so much that less of the really vibrant blue makes it directly to your eye
411.360000    417.760000     All that re-scattering mixes things up and it starts to look paler more diluted. Sometimes even whitish interesting
417.760000    424.160000     So the amount of air matters. What about places with less air like if you go way up a mountain or I don't know the moon
424.160000    428.400000     Perfect question. Let's take the mountain first if you're high up maybe on a tall peak. Yeah
428.400000    436.000000     You might notice the sky directly overhead looks a really deep dark blue almost purple-ish blue sometimes why darker?
436.000000    439.600000     Because there are fewer air molecules above you at that altitude
440.080000    445.520000     Fewer molecules mean less scattering overall so less blue light is being scattered away before it reaches you
445.520000    449.680000     You get a more direct view almost. Okay less air darker blue now
449.680000    456.560000     The moon what happens there it has basically no air right exactly the moon has virtually no atmosphere
456.560000    460.880000     Scientists call it an exosphere which basically means the air is so incredibly thin
460.880000    468.720000     Molecules hardly ever even bump into each other let alone scatter light effectively and no scattering pretty much none and the result is
469.360000    474.000000     Well, it's kind of mind-blowing whether it's daytime on the moon with the sun shining or nighttime
474.000000    478.640000     Hmm the sky is always black always black even with the sun up always black
478.640000    483.520000     You'd see the sun as a brilliant disc and you'd see the stars all against a totally black background
483.520000    487.040000     There's just nothing there to scatter the sunlight and make the sky glow wow
487.040000    492.800000     That really makes you appreciate our atmosphere doesn't a black sky during the day while
492.800000    497.200000     Okay, let's talk about the other big color show sunrises and sunsets
497.760000    500.160000     Those incredible reds oranges pinks
500.160000    505.760000     They're just spectacular. They really are and it's the same science just amplified
505.760000    509.680000     Remember how looking at the horizon means looking through more air yeah
509.680000    513.440000     Well at sunrise and sunset the sun is right on the horizon
513.440000    518.480000     So it's light has to travel through the absolute maximum amount of atmosphere to reach your eyes
518.480000    523.920000     Way more than even looking at the horizon at noon. Okay. It's the longest possible path through the air
524.160000    529.360000     Exactly. It's like the light has to run this incredibly long obstacle course through the atmosphere
529.360000    536.240000     And because that path is so long even more of the blue light and even the green light gets scattered away
536.240000    539.120000     It bounces off in other directions so much
539.120000    542.480000     It's basically filtered out from the light that reaches you directly
542.480000    544.480000     So if the blues and greens are scattered away
544.480000    552.720000     What's left what's left are the colors that scatter the least the longer wavelengths the reds the oranges the yellows the pinks
552.960000    558.880000     Those are the colors that manage to push through that long dense path of air and make it all the way to your eyes
558.880000    563.920000     So they dominate the view painting the clouds in the sky with those amazing warm colors
563.920000    568.320000     That makes perfect sense. It's like filtering out the blue pretty much and here is a little bonus
568.320000    577.440000     Sometimes sunsets are even more spectacular right really fiery red. Yeah. Why is that that often happens when there are larger particles in the air
577.760000    584.800000     Things like dust or smoke from fires pollution even tiny water droplets or ice crystals in clouds
584.800000    589.760000     After a big volcanic eruption for instance, you can get amazing sunsets for months
589.760000    592.320000     How do those particles change things
592.320000    597.520000     Those larger particles are also really good at scattering the longer wavelengths the reds and yellows
597.520000    605.440000     So they not only let the red light through they help scatter it around the sky and you're the sun making the whole scene glow even more intensely
605.600000    613.360000     Fascinating. Okay, we've talked earth's atmosphere. Mm-hmm. You mentioned other planets. Mm-hmm. Is the sky blue everywhere or does it depend?
613.360000    619.040000     It totally depends. It's all about what's in the atmosphere earth sky is blue because we have lots of nitrogen and oxygen doing that
619.040000    621.840000     Rayleigh scattering so other planets different atmospheres
621.840000    626.000000     Take Mars Mars is a great example because it's so different. Okay Mars
626.000000    632.400000     What's its sky like? Well first Mars has a very thin atmosphere less than 1% of earth's pressure
632.800000    638.880000     And it's mostly carbon dioxide, but the key thing is it's usually full of fine reddish dust red dust
638.880000    646.080000     So during the Martian day that dust scatters sunlight, but dust particles scatter differently than our tiny gas molecules
646.080000    655.600000     They tend to scatter red light forward making the sky generally look kind of hazy orange or butterscotch or reddish brown depending on how much dust is up there and orange sky
655.600000    660.960000     Okay, but here's where it gets really weird and kind of cool Mars sunsets
661.200000    666.720000     What about them? Are they red like ours? Nope. They're blue. Blue sunsets. Yeah on the red planet. Yeah
666.720000    673.200000     Right around the setting sun the sky takes on this distinct blue-ish glow. It's the opposite of earth. How does that work?
673.200000    675.360000     It's those dust particles again
675.360000    682.640000     They scatter red light all over the sky during the day, but they scatter blue light mostly forward in the direction the light is traveling
682.640000    685.920000     So at sunset when you're looking towards the sun through the most dust
686.400000    691.440000     That forward scattered blue light becomes concentrated right around the sun's disc making it look blue
691.440000    694.560000     While the rest of the sky might still look yellowish or reddish
694.560000    696.000000     That is
696.000000    699.680000     Completely backwards from earth a blue sunset wow
699.680000    706.080000     Isn't it wild it just shows how much the specific composition of an atmosphere dictates what you see it really does
706.080000    711.280000     What stands out to you most about all these different sky colors seeing how planets can be so different?
711.280000    716.320000     I think it just highlights how special earth conditions are you know and how interconnected everything is
716.640000    719.760000     But also it connects to something really practical. Oh, yeah. What's that?
719.760000    722.560000     Well, okay, we enjoy the blue sky the pretty sunsets
722.560000    728.880000     But why does understanding the scattering really matter beyond just well appreciating the view good question
728.880000    732.160000     Why should we care? Because sunlight isn't just light. It's energy
732.160000    735.680000     It's what heats our planet drives weather powers life
735.680000    744.480000     And how that light gets scattered or reflected or absorbed by different things forests oceans ice caps clouds pollution particles
744.960000    752.400000     Greenhouse gases that directly affects earth's energy balance our climate. Oh, okay, so scattering affects climate
752.400000    755.120000     Absolutely and this whole light scattering principle
755.120000    761.040000     It's exactly how we monitor the planet from space. It's the basis for remote sensing remote sensing
761.040000    767.200000     Like satellites looking down precisely satellites like the GOES weather satellites run by NOAA for example
767.200000    773.200000     They have instruments that measure the intensity of light reflecting off earth at different wavelengths different colors essentially
773.520000    780.720000     By analyzing that scattered and reflected light scientists can figure out all sorts of things without ever leaving orbit like what? Oh tons
780.720000    784.960000     Surface temperatures ocean temperatures. How much water vapor is in the air?
784.960000    793.200000     Levels of carbon dioxide or pollutants like ozone or smoke particles where clouds are how healthy vegetation is all from just looking at scattered light
793.200000    797.360000     All from carefully measuring how sunlight interacts with the atmosphere in the surface
797.440000    804.400000     It's fundamental to weather forecasting tracking storms understanding climate change monitoring air quality
804.400000    813.760000     Everything so that simple question. Why is the sky blue? It actually leads right to the heart of how we understand and monitor our entire planet
813.760000    821.520000     Exactly. It's not just a curiosity. It's fundamental earth science. Wow. Okay, so the next time any of us look up at that blue sky
821.520000    827.280000     Or maybe catch a fiery sunset or even see pictures of that weird blue sunset on Mars
827.600000    831.840000     We should remember it's not the ocean's reflection not at all. It's this incredible
831.840000    840.000000     dynamic physics experiment playing out constantly above us tiny molecules tiny waves of light doing this intricate dance
840.000000    846.880000     It really isn't it just shows doesn't it even the most familiar things things we see every single day are packed with amazing science
846.880000    850.480000     Complex yeah, but totally understandable once you break it down
850.480000    852.160000     Yeah, let me see you look at the world a bit differently
852.160000    855.200000     It's a great reminder that there's always more going on than meets the eye
855.600000    860.320000     Always more to learn more to appreciate even just looking up definitely and it makes you think
860.320000    864.800000     What else looks simple, but it's actually super complex like
864.800000    869.440000     Why is the ocean itself blue is that reflect in the sky? Huh
869.440000    876.080000     Good follow-up and no the ocean isn't blue because it reflects the sky theater though that adds a little bit sometimes
876.080000    882.480000     Mostly the ocean is blue because water molecules themselves are surprisingly good at absorbing the longer wavelengths of light
882.960000    887.200000     The reds oranges yellow the water eats the red light. Yeah, it absorbs it
887.200000    889.840000     But it's not so good at absorbing blue light
889.840000    895.520000     So the blue light penetrates deeper gets scattered by the water molecules and eventually reflected back out for us to see
895.520000    902.720000     So water itself has an intrinsic blue color in large volumes another physics mystery salt or well explained
902.720000    906.320000     We really hope this deep dive into why the sky is blue leaves you feeling
906.320000    910.080000     Well-informed and maybe looking at the sky with some fresh curiosity
910.480000    917.120000     Keep asking those questions those simple questions often have the most fascinating answers and that wraps up today's episode of every day explained
917.120000    920.480000     We love making sense of the world around you five days a week
920.480000    925.680000     If you enjoyed today's deep dive consider subscribing so you don't miss out on our next discovery
925.680000    927.920000     I'm Chris and I'll catch you in the next one