WEBVTT 00:00:00.000 --> 00:00:02.740 Everyone thinks sunset is just, you know, a simple 00:00:02.740 --> 00:00:04.980 off -switch. Right. Day turns to night. Exactly. 00:00:05.120 --> 00:00:07.480 You watch the sun drop below the horizon, the 00:00:07.480 --> 00:00:10.199 sky gets dark, and you just assume the show is 00:00:10.199 --> 00:00:12.919 completely over. I mean, it's the ultimate binary, 00:00:13.220 --> 00:00:16.399 right? We're totally wired to see it as this 00:00:16.399 --> 00:00:19.500 clean break between light and new light. If you 00:00:19.500 --> 00:00:22.760 know exactly when to look, specifically when 00:00:22.760 --> 00:00:25.320 the sun hits that sweet spot between two and 00:00:25.320 --> 00:00:27.660 six degrees below the horizon, you can actually 00:00:27.660 --> 00:00:31.480 see this massive hidden atmospheric machine that 00:00:31.480 --> 00:00:33.560 controls our sky. Yeah, it really is a machine. 00:00:33.679 --> 00:00:37.109 It is. And welcome to this deep dive. Today, 00:00:37.429 --> 00:00:40.009 our mission is to completely transform how you 00:00:40.009 --> 00:00:43.270 look up after the sun goes down. We're pulling 00:00:43.270 --> 00:00:45.789 from this fascinating Wikipedia deep dive on 00:00:45.789 --> 00:00:48.250 the atmospheric optical phenomenon known as the 00:00:48.250 --> 00:00:51.530 afterglow, and its morning equivalent, the foreglow. 00:00:51.649 --> 00:00:53.509 Yeah, we're going to unpack the hidden physics 00:00:53.509 --> 00:00:56.450 of light frequencies, some pretty dramatic historical 00:00:56.450 --> 00:00:58.810 events that, you know, permanently altered our 00:00:58.810 --> 00:01:01.789 skies, and the visual masterpiece is hiding right 00:01:01.789 --> 00:01:04.549 there in the quiet light. But to really grasp 00:01:04.549 --> 00:01:07.810 what is happening above our heads, we have to 00:01:07.810 --> 00:01:11.450 stop looking at the sky as an empty void. OK. 00:01:11.829 --> 00:01:13.730 We have to start looking at it as a physical 00:01:13.730 --> 00:01:17.250 medium. The atmosphere is basically this dense 00:01:17.250 --> 00:01:20.209 soup of gases, suspended dust, and aerosols. 00:01:20.329 --> 00:01:23.170 A soup. I like that. Yeah. So when you see an 00:01:23.170 --> 00:01:26.829 afterglow, that broad arch of whitish or pinkish 00:01:26.829 --> 00:01:29.010 sunlight that just kind of lingers in the twilight, 00:01:29.510 --> 00:01:31.930 you aren't just seeing light. Right. You are 00:01:31.930 --> 00:01:35.469 witnessing a highly complex mechanical collision 00:01:35.469 --> 00:01:39.269 between specific light frequencies and that atmospheric 00:01:39.269 --> 00:01:42.670 soup. OK, let's unpack this. Because to truly 00:01:42.670 --> 00:01:44.950 understand this phenomenon, we literally have 00:01:44.950 --> 00:01:47.409 to dismantle the sky. Exactly. We have to look 00:01:47.409 --> 00:01:49.489 at the mechanical ingredients. So let's start 00:01:49.489 --> 00:01:51.469 with the baseline physics before we even get 00:01:51.469 --> 00:01:53.469 to the afterglow itself. Sure. Let's talk about 00:01:53.469 --> 00:01:56.349 the golden hour right before sunset. Why does 00:01:56.349 --> 00:01:58.409 the light suddenly look so, I don't know, heavy 00:01:58.409 --> 00:02:00.510 and red? Well, it really comes down to the physical 00:02:00.510 --> 00:02:02.709 shape of the light waves. Sunlight looks white 00:02:02.709 --> 00:02:05.310 to us, but it's actually a spectrum of different 00:02:05.310 --> 00:02:07.969 colors, which are really just different frequencies 00:02:07.969 --> 00:02:10.189 of energy. Like a rainbow. Right. So blue light 00:02:10.189 --> 00:02:13.229 is high energy. Its waveforms are short, tight, 00:02:13.430 --> 00:02:15.810 and choppy. Red light is the opposite. It's low 00:02:15.810 --> 00:02:19.289 energy with long rolling waveforms. Now when 00:02:19.289 --> 00:02:22.270 the sun is high in the sky at noon, its light 00:02:22.270 --> 00:02:24.469 is shining straight down through the thinnest 00:02:24.469 --> 00:02:26.650 part of the atmosphere. So it's taking the shortest 00:02:26.650 --> 00:02:29.310 possible path to our eyes. Right. But as the 00:02:29.310 --> 00:02:32.169 sun drops toward the horizon, the angle changes 00:02:32.169 --> 00:02:35.789 drastically. Yeah, obviously. So now that exact 00:02:35.789 --> 00:02:39.419 same sunlight has to punch horizontally. through 00:02:39.419 --> 00:02:41.719 a much thicker slice of the Earth's atmosphere 00:02:41.719 --> 00:02:44.479 to actually reach you. Like the thicker the atmospheric 00:02:44.479 --> 00:02:47.060 onion, the more brutal the filter. That's a great 00:02:47.060 --> 00:02:49.159 way to put it. And this is where this mechanism 00:02:49.159 --> 00:02:51.379 called Rayleigh scattering takes over. Rayleigh 00:02:51.379 --> 00:02:53.699 scattering. Yeah. Remember those short, choppy 00:02:53.699 --> 00:02:55.560 blue light waves? Right, the high energy ones. 00:02:55.680 --> 00:02:58.860 They cannot survive that long journey through 00:02:58.860 --> 00:03:01.939 the dense lower atmosphere. They basically crash 00:03:01.939 --> 00:03:05.409 into oxygen and nitrogen molecules and just get 00:03:05.409 --> 00:03:07.569 scattered away in every single direction. Oh, 00:03:07.650 --> 00:03:10.289 wow. So they just get bounced out. Exactly. By 00:03:10.289 --> 00:03:12.189 the time the sunlight reaches your eyes at the 00:03:12.189 --> 00:03:15.740 golden hour, all those fragile blue and green 00:03:15.740 --> 00:03:18.539 wavelengths have been completely obliterated 00:03:18.539 --> 00:03:20.680 from the direct beam. Leaving only the heavy 00:03:20.680 --> 00:03:23.680 hitters. You've got it. The long rolling low 00:03:23.680 --> 00:03:26.780 frequency red waves that can just bulldoze their 00:03:26.780 --> 00:03:28.560 way through the thickest part of the atmosphere. 00:03:28.740 --> 00:03:32.020 That intensely low frequency red component is 00:03:32.020 --> 00:03:34.819 what survives. But the machinery we really care 00:03:34.819 --> 00:03:37.439 about today kicks into high gear during what's 00:03:37.439 --> 00:03:40.180 called civil twilight. Right. When the sun physically 00:03:40.180 --> 00:03:42.900 drops below the horizon line. Exactly. The direct 00:03:42.900 --> 00:03:45.819 beam is gone. Yeah. The sky is still glowing 00:03:45.819 --> 00:03:47.900 red. Wait, let me make sure I'm visualizing the 00:03:47.900 --> 00:03:50.680 mechanics here. Sure. If the light source -like, 00:03:50.960 --> 00:03:52.960 the sun itself, is physically blocked by the 00:03:52.960 --> 00:03:55.259 curvature of the Earth, how is that red light 00:03:55.259 --> 00:03:57.960 still reaching my eyes? Backscattering. Backscattering. 00:03:58.020 --> 00:03:59.919 Remember that atmospheric soup we talked about? 00:04:00.039 --> 00:04:03.800 The dust and aerosols? Right. The air is full 00:04:03.800 --> 00:04:07.419 of particulate matter. Dust, pollen, volcanic 00:04:07.419 --> 00:04:10.900 ash. pollution. Even though the sun is technically 00:04:10.900 --> 00:04:14.120 below your horizon, its low frequency red rays 00:04:14.120 --> 00:04:16.339 are still shooting straight across the lower 00:04:16.339 --> 00:04:18.939 atmosphere, just above your head. Oh, I see. 00:04:19.300 --> 00:04:21.759 So those red rays hit the suspended particles 00:04:21.759 --> 00:04:24.980 in the air, bounce off them, and scatter back 00:04:24.980 --> 00:04:27.259 down toward the ground. That makes total sense. 00:04:27.480 --> 00:04:29.680 Yeah, sometimes they reflect off clouds or even 00:04:29.680 --> 00:04:32.000 high snow fields. That backscattering is exactly 00:04:32.000 --> 00:04:34.459 what paints the sky with that lingering reddish 00:04:34.459 --> 00:04:36.920 -pink glow. So we have red light bouncing off 00:04:36.920 --> 00:04:39.899 dust in the lower atmosphere, but the absolute 00:04:39.899 --> 00:04:41.939 showstopper of this whole sequence is something 00:04:41.939 --> 00:04:43.839 called the purple light. Yes, the purple light. 00:04:44.040 --> 00:04:46.839 And this happens specifically during civil twilight, 00:04:47.139 --> 00:04:49.939 when the sun is exactly between 2 and 6 degrees 00:04:49.939 --> 00:04:52.540 below the horizon. That's the sweet spot. But 00:04:52.540 --> 00:04:54.399 wait, if the red light we just talked about is 00:04:54.399 --> 00:04:56.759 low energy, and the blue light is high energy, 00:04:57.160 --> 00:04:59.180 how on earth are they mixing to create purple? 00:04:59.379 --> 00:05:01.689 It's a bit of a mind bender. Because if the atmosphere 00:05:01.689 --> 00:05:04.350 is acting like this brutal filter obliterating 00:05:04.350 --> 00:05:06.649 the blue light, where is the blue coming from? 00:05:06.990 --> 00:05:08.350 Well, you have to think about the atmosphere 00:05:08.350 --> 00:05:11.170 in three dimensions, not just as a flat ceiling 00:05:11.170 --> 00:05:14.410 above us. OK. At that highly specific two to 00:05:14.410 --> 00:05:18.269 six degree angle, you get this perfect structural 00:05:18.269 --> 00:05:21.009 overlap of two completely different atmospheric 00:05:21.009 --> 00:05:24.149 layers. Two layers. Down low, near the ground, 00:05:24.750 --> 00:05:27.670 you have the surviving low frequency red light 00:05:27.670 --> 00:05:30.399 backscattering off the dust. just like we discussed. 00:05:30.620 --> 00:05:33.199 Our surviving heavy hitters. Right. But look 00:05:33.199 --> 00:05:36.199 higher up, miles above your head, up in the upper 00:05:36.199 --> 00:05:39.220 atmosphere, the air is much thinner. Oh, right. 00:05:39.360 --> 00:05:41.560 The sun is still illuminating that high altitude 00:05:41.560 --> 00:05:44.379 layer. And because the air is thinner up there, 00:05:44.819 --> 00:05:47.060 the short high energy blue light waves aren't 00:05:47.060 --> 00:05:49.300 getting obliterated yet. They're surviving. Yeah, 00:05:49.319 --> 00:05:51.180 they're doing their normal thing, just scattering 00:05:51.180 --> 00:05:55.019 broadly across the sky. And this broad high altitude 00:05:55.019 --> 00:05:57.980 blue light. actually belongs to the darker phase 00:05:57.980 --> 00:06:00.600 of twilight, known as nautical twilight. Oh, 00:06:00.600 --> 00:06:02.279 I see. So your eyes are playing a trick on you. 00:06:02.439 --> 00:06:04.160 Basically, yeah. You're standing on the ground 00:06:04.160 --> 00:06:06.620 looking up through a lower layer of backscattered 00:06:06.620 --> 00:06:09.699 red light straight into a much higher layer of 00:06:09.699 --> 00:06:12.639 scattered blue light. Exactly. Our eyes compress 00:06:12.639 --> 00:06:15.600 those miles of vertical depth into a single flat 00:06:15.600 --> 00:06:18.720 visual canvas. We just see the physical intersection 00:06:18.720 --> 00:06:21.120 of two completely different energy frequencies 00:06:21.120 --> 00:06:23.459 stacked on top of each other. Red layered over 00:06:23.459 --> 00:06:26.480 blue. Which... equals the purple light. It's 00:06:26.480 --> 00:06:28.660 literally the visual mixing of civil twilight 00:06:28.660 --> 00:06:31.379 and nautical twilight. That is so cool. And anchoring 00:06:31.379 --> 00:06:34.699 this whole visual display is the bright segment, 00:06:34.899 --> 00:06:36.740 which is that part that lingers right at the 00:06:36.740 --> 00:06:39.699 horizon until nautical twilight completely takes 00:06:39.699 --> 00:06:42.579 over and true darkness sets in. Yeah, the bright 00:06:42.579 --> 00:06:45.819 segment is kind of the last gasp of that forward 00:06:45.819 --> 00:06:48.819 scattered sunlight. Yeah. And while we are breaking 00:06:48.819 --> 00:06:50.959 down the cold physics of this, we really can't 00:06:50.959 --> 00:06:53.810 ignore the human impact. Definitely. This specific 00:06:53.810 --> 00:06:55.889 scattering, particularly when the high frequency 00:06:55.889 --> 00:06:58.670 blue light dominates just before or after that 00:06:58.670 --> 00:07:01.129 reddish glow, creates what we call the blue hour. 00:07:01.310 --> 00:07:04.269 The blue hour. It's this fleeting window of time 00:07:04.269 --> 00:07:06.769 that painters and photographers have just treasured 00:07:06.769 --> 00:07:10.389 for centuries. The ambient sort of omnidirectional 00:07:10.389 --> 00:07:13.269 quality of that scattered blue light provides 00:07:13.269 --> 00:07:16.449 an atmospheric depth that is physically impossible 00:07:16.449 --> 00:07:19.170 to replicate with a flash or artificial lighting. 00:07:19.370 --> 00:07:21.589 So we have this highly delicate balance of red 00:07:21.589 --> 00:07:24.430 and blue light acting as our baseline, a canvas 00:07:24.430 --> 00:07:26.910 provided by the natural dust and geometry of 00:07:26.910 --> 00:07:28.829 the Earth. Right. Here's where it gets really 00:07:28.829 --> 00:07:32.269 interesting. What happens to that fragile equation 00:07:32.269 --> 00:07:35.290 if you violently dump billions of tons of ash 00:07:35.290 --> 00:07:37.850 into the stratosphere? Well, it completely breaks 00:07:37.850 --> 00:07:40.350 the standard physics. You move instantly from 00:07:40.350 --> 00:07:42.769 everyday meteorology into the realm of world 00:07:42.769 --> 00:07:45.339 -changing historical events. because the amount 00:07:45.339 --> 00:07:48.079 of particulate matter in the air is the ultimate 00:07:48.079 --> 00:07:50.079 variable in an afterglow. So let's talk about 00:07:50.079 --> 00:07:52.779 the phenomenon of volcanic purple light, specifically 00:07:52.779 --> 00:07:56.759 the 1883 eruption of Krakatoa in Indonesia. Oh, 00:07:56.879 --> 00:07:59.160 Krakatoa. This wasn't just a standard geological 00:07:59.160 --> 00:08:02.000 event, it was an explosion so monumentally massive 00:08:02.000 --> 00:08:05.189 that it literally ruptured the sky. Yeah, Krakatoa 00:08:05.189 --> 00:08:08.449 blew this incomprehensible volume of exceedingly 00:08:08.449 --> 00:08:12.269 fine, pulverized rock and ash straight up into 00:08:12.269 --> 00:08:14.689 the stratosphere. That's massive amounts. We 00:08:14.689 --> 00:08:16.529 are talking about altitudes where commercial 00:08:16.529 --> 00:08:19.689 jets fly today and even higher than that. And 00:08:19.689 --> 00:08:21.910 it obviously didn't just stay hovering over Indonesia. 00:08:22.170 --> 00:08:24.649 Not at all. High atmospheric winds caught that 00:08:24.649 --> 00:08:27.370 unbelievably fine dust and basically used it 00:08:27.370 --> 00:08:29.509 to wrap the entire planet. It became a global 00:08:29.509 --> 00:08:31.889 diffusion. It's like imagine throwing a massive 00:08:31.889 --> 00:08:34.330 handful of glitter straight into a projector 00:08:34.330 --> 00:08:36.429 beam. That's a great visual. Suddenly the light 00:08:36.429 --> 00:08:38.769 isn't just passing through empty space. It's 00:08:38.769 --> 00:08:41.470 aggressively bouncing off millions of new surfaces. 00:08:42.330 --> 00:08:45.269 The Krakatoa ash provided trillions of microscopic 00:08:45.269 --> 00:08:47.570 mirrors suspended globally in the stratosphere. 00:08:47.789 --> 00:08:49.919 Exactly. It took the standard physics of the 00:08:49.919 --> 00:08:52.080 afterglow and turned the volume all the way up 00:08:52.080 --> 00:08:55.039 to maximum. Wow. For months, people all over 00:08:55.039 --> 00:08:57.360 the globe were suddenly seeing a worldwide series 00:08:57.360 --> 00:09:00.899 of intensely magnified red sunsets and volcanic 00:09:00.899 --> 00:09:03.379 purple light. The low frequency red light just 00:09:03.379 --> 00:09:07.080 had this unimaginably vast new canvas of particulate 00:09:07.080 --> 00:09:09.600 matter to backscatter against. See, I want to 00:09:09.600 --> 00:09:11.700 push back on this a little though. How is it 00:09:11.700 --> 00:09:15.480 that an event so incredibly violent, so destructive 00:09:15.480 --> 00:09:18.899 at its epicenter, translates into a lasting, 00:09:19.240 --> 00:09:22.580 beautiful visual phenomenon halfway across the 00:09:22.580 --> 00:09:25.500 globe? What's fascinating here is that monumental 00:09:25.500 --> 00:09:28.659 geological events don't just shape the ground 00:09:28.659 --> 00:09:31.779 beneath us. Okay. They actively alter our visual 00:09:31.779 --> 00:09:34.799 reality on a global scale. And that altered visual 00:09:34.799 --> 00:09:37.840 reality permanently changed art history. It really 00:09:37.840 --> 00:09:40.450 did. Think about Edvard Munch's famous painting, 00:09:40.649 --> 00:09:42.809 The Scream. You know, the one, the agonizing 00:09:42.809 --> 00:09:45.169 bald figure holding its face on a bridge. Right, 00:09:45.370 --> 00:09:48.269 set against this swirling, chaotic, blood red 00:09:48.269 --> 00:09:51.309 and orange sky. Exactly. Yeah. And for decades, 00:09:51.570 --> 00:09:53.629 people assumed that sky was purely psychological, 00:09:53.970 --> 00:09:56.210 like a metaphor for the figure's internal dread. 00:09:56.730 --> 00:09:59.269 But it's actually an observational record. The 00:09:59.269 --> 00:10:01.570 timeline aligns perfectly with the global diffusion 00:10:01.570 --> 00:10:04.029 of the Krakatoa dust cloud over Europe. Munch 00:10:04.029 --> 00:10:06.850 was known to paint exactly what he saw. He wasn't 00:10:06.850 --> 00:10:09.549 painting an emotional metaphor. He was documenting 00:10:09.549 --> 00:10:12.830 the literal hyper -intensified red -back scattering 00:10:12.830 --> 00:10:15.529 of the volcanic purple light forced into the 00:10:15.529 --> 00:10:18.309 atmosphere by Krakatoa. A geological rupture 00:10:18.309 --> 00:10:20.990 in the southern hemisphere becomes an iconic 00:10:20.990 --> 00:10:23.789 visual masterpiece in the northern hemisphere. 00:10:23.990 --> 00:10:26.570 It's incredible. It just reinforces this profound 00:10:26.570 --> 00:10:29.610 idea that everything in the natural world is 00:10:29.610 --> 00:10:32.809 deeply physically interconnected. And this isn't 00:10:32.809 --> 00:10:35.110 just a 19th century phenomenon either. Right. 00:10:35.309 --> 00:10:37.549 If you look at modern photographic records of 00:10:37.549 --> 00:10:40.789 afterglows, you see an intensely vivid, bruised 00:10:40.789 --> 00:10:44.029 purple sunset over Hong Kong shortly after the 00:10:44.029 --> 00:10:47.110 1991 eruption of Mount Pinatubo in the Philippines. 00:10:47.210 --> 00:10:50.570 Wow. You see the exact same particulates scattering 00:10:50.570 --> 00:10:53.750 over skyscrapers in Taiwan, housing estates in 00:10:53.750 --> 00:10:56.990 Krakow, a pier in Australia, a college track 00:10:56.990 --> 00:10:59.610 in Maine, and the city of Dresden in Germany. 00:10:59.679 --> 00:11:02.419 because the physics are entirely agnostic. Exactly. 00:11:02.740 --> 00:11:05.220 A long red wavelength will backscatter off a 00:11:05.220 --> 00:11:08.340 volcanic ash particle exactly the same way over 00:11:08.340 --> 00:11:10.980 a housing estate in Poland as it will over a 00:11:10.980 --> 00:11:13.639 track in Maine. The mechanical constants of the 00:11:13.639 --> 00:11:15.320 atmosphere do not care what is on the ground 00:11:15.320 --> 00:11:17.539 below. The physics are a constant, sure, but 00:11:17.539 --> 00:11:19.860 where you are standing on the ground drastically 00:11:19.860 --> 00:11:22.360 alters how you perceive those physics. We've 00:11:22.360 --> 00:11:26.059 explored how a global extreme, like a massive 00:11:26.059 --> 00:11:29.679 volcano, injects chaos into the afterglow. Let's 00:11:29.679 --> 00:11:32.799 look at how geographic extremes warp the experience. 00:11:33.259 --> 00:11:35.179 Well, elevation is the most immediate modifier. 00:11:35.519 --> 00:11:37.940 In mountainous regions, we see a specific variation 00:11:37.940 --> 00:11:40.590 of the afterglow called Alpenglow. Right. So 00:11:40.590 --> 00:11:43.110 imagine standing deep in the Triglav Lakes Valley 00:11:43.110 --> 00:11:46.149 in the Julian Alps. The sun has already dipped 00:11:46.149 --> 00:11:48.850 behind the jagged peaks. You are standing in 00:11:48.850 --> 00:11:52.769 the cold, dark shadows of civil twilight. But 00:11:52.769 --> 00:11:55.990 when you look up at the highest snowfields. Those 00:11:55.990 --> 00:11:58.509 high elevation snowfields are still physically 00:11:58.509 --> 00:12:01.330 catching the direct or scattered light that the 00:12:01.330 --> 00:12:03.850 valley floor has already lost. Oh, wow. The mountains 00:12:03.850 --> 00:12:06.250 are acting as a massive geological projection 00:12:06.250 --> 00:12:08.929 screen. The golden -red light reflects brightly 00:12:08.929 --> 00:12:11.389 off the peaks, functioning very similarly to 00:12:11.389 --> 00:12:13.370 another optical phenomenon called the Belt of 00:12:13.370 --> 00:12:15.730 Venus, where that pinkish band sits just above 00:12:15.730 --> 00:12:18.009 the horizon. But the timeline of Alpenglo is 00:12:18.009 --> 00:12:20.090 what really fascinates me, because the absolute 00:12:20.090 --> 00:12:22.590 final stage of Alpenglo occurs specifically when 00:12:22.590 --> 00:12:24.669 the purple light is reflected. Right, because 00:12:24.669 --> 00:12:27.029 those peaks are so incredibly high. They catch 00:12:27.029 --> 00:12:30.450 that specific 2 to 6 degree intersection of backscattered 00:12:30.450 --> 00:12:33.190 red and high -altitude blue light. So you are 00:12:33.190 --> 00:12:35.470 standing in darkness down below. Yeah, and the 00:12:35.470 --> 00:12:38.679 mountaintops... Miles above you are glowing a 00:12:38.679 --> 00:12:42.419 surreal, vibrant purple. OK, so elevation creates 00:12:42.419 --> 00:12:45.700 a projection screen. But what happens if we push 00:12:45.700 --> 00:12:49.019 the geography to the absolute extreme, like the 00:12:49.019 --> 00:12:52.399 bottom of the Earth, the South Pole? Ah, the 00:12:52.399 --> 00:12:55.840 South Pole foreglow. This is where the geometry 00:12:55.840 --> 00:12:57.720 of the Earth stretches the physics we've been 00:12:57.720 --> 00:13:00.440 talking about into something almost unrecognizable. 00:13:00.740 --> 00:13:03.200 How so? At the Earth's poles, the sun doesn't 00:13:03.200 --> 00:13:06.009 rise and set every day. It only appears at the 00:13:06.009 --> 00:13:08.490 horizon around the equinox. Which marks the transition 00:13:08.490 --> 00:13:10.809 between a half -year -long polar night and a 00:13:10.809 --> 00:13:13.230 half -year -long polar day. Exactly. So put yourself 00:13:13.230 --> 00:13:15.210 in the boots of a researcher stationed out there 00:13:15.210 --> 00:13:17.049 on the ice. You haven't seen the sun in nearly 00:13:17.049 --> 00:13:19.809 six months. That's intense. Your body's circadian 00:13:19.809 --> 00:13:22.350 rhythm is completely starved of daylight. You 00:13:22.350 --> 00:13:24.549 are living in a permanent, freezing, nautical 00:13:24.549 --> 00:13:27.279 twilight or total darkness. The psychological 00:13:27.279 --> 00:13:29.559 weight of that environment has to be staggering. 00:13:30.460 --> 00:13:33.340 But then, days before the Sun even physically 00:13:33.340 --> 00:13:37.019 breaches the horizon, the sky starts changing. 00:13:37.299 --> 00:13:40.059 Because of the equator, the Sun drops vertically. 00:13:40.960 --> 00:13:43.419 Sunset takes, what, 20 minutes? Yeah, pretty 00:13:43.419 --> 00:13:45.419 quick. But because of the severe tilt of the 00:13:45.419 --> 00:13:48.419 Earth at the poles, the Sun approaches the horizon 00:13:48.419 --> 00:13:52.980 at an incredibly shallow agonizingly slow angle. 00:13:53.220 --> 00:13:55.799 So what does this all mean? It's like the Earth's 00:13:55.799 --> 00:13:59.080 geometry is acting as a massive slow motion dimmer 00:13:59.080 --> 00:14:02.059 switch. That is exactly it. The low energy red 00:14:02.059 --> 00:14:04.080 light begins pushing through the thickest possible 00:14:04.080 --> 00:14:06.399 horizontal slice of the atmosphere. The heavy 00:14:06.399 --> 00:14:08.740 atmospheric refraction bends that light over 00:14:08.740 --> 00:14:10.879 the curvature of the earth, allowing it to reach 00:14:10.879 --> 00:14:13.000 the south pole longer for the physical body the 00:14:13.000 --> 00:14:15.320 sun does. So instead of a 20 minute forglow, 00:14:15.320 --> 00:14:17.340 you get this atmospheric machinery stretched 00:14:17.340 --> 00:14:19.899 to its absolute temporal limits. You get days 00:14:19.899 --> 00:14:22.700 of this agonizingly slow build up of refracted 00:14:22.700 --> 00:14:25.059 red and purple light, just this glowing promise 00:14:25.059 --> 00:14:27.580 on the horizon fighting against a six month night. 00:14:27.879 --> 00:14:30.879 If we connect this to bigger picture. It proves 00:14:30.879 --> 00:14:33.799 that our perception of light, color, and even 00:14:33.799 --> 00:14:37.139 time is entirely relative. Totally relative. 00:14:37.320 --> 00:14:40.279 The physics are identical. The railings scattering, 00:14:40.559 --> 00:14:42.899 stripping away the blue light. The low frequency 00:14:42.899 --> 00:14:45.179 red waves punching through. The back scattering 00:14:45.179 --> 00:14:48.000 off suspended ice crystals or dust. It is the 00:14:48.000 --> 00:14:50.340 exact same mechanical process happening over 00:14:50.340 --> 00:14:53.179 a driveway in Ohio. Right. But the extreme geography 00:14:53.179 --> 00:14:56.220 of the South Pole turns a passing daily moment 00:14:56.220 --> 00:15:00.200 into a prolonged monumental event. It really 00:15:00.200 --> 00:15:02.240 is a master class in physics happening right 00:15:02.240 --> 00:15:04.620 above our heads every single day completely ignored 00:15:04.620 --> 00:15:06.759 by most of us. Oh absolutely. We started this 00:15:06.759 --> 00:15:09.259 deep dive talking about how simple a sunset seems 00:15:09.259 --> 00:15:12.059 day to night but when we actually dismantled 00:15:12.059 --> 00:15:15.259 the sky we found a highly sensitive machine. 00:15:15.399 --> 00:15:18.320 A delicate balance. Yeah. We found that the golden 00:15:18.320 --> 00:15:21.019 hour is just a brutal filtering process, leaving 00:15:21.019 --> 00:15:24.320 only long, heavy red wavelengths. We found that 00:15:24.320 --> 00:15:26.799 when the sun hits that specific sweet spot of 00:15:26.799 --> 00:15:29.840 two to six degrees below the horizon, the surviving 00:15:29.840 --> 00:15:32.539 red rays in the lower atmosphere stack perfectly 00:15:32.539 --> 00:15:34.799 beneath the scattered blue rays of the upper 00:15:34.799 --> 00:15:37.460 atmosphere, tricking our eyes into seeing the 00:15:37.460 --> 00:15:41.210 purple light of civil twilight. And we saw how 00:15:41.210 --> 00:15:43.590 injecting massive amounts of fine particulate 00:15:43.590 --> 00:15:46.850 dust into that fragile equation like Krakatoa, 00:15:46.850 --> 00:15:49.409 violently exploding into the stratosphere, can 00:15:49.409 --> 00:15:52.149 paint global masterpieces across the sky. Leaving 00:15:52.149 --> 00:15:54.509 observational records and iconic art like the 00:15:54.509 --> 00:15:56.429 Scream. Exactly. And we discovered that your 00:15:56.429 --> 00:15:58.330 location on the planet, whether you're using 00:15:58.330 --> 00:16:00.529 the jagged peaks of the Alps as a projection 00:16:00.529 --> 00:16:03.850 screen for Alpenglow or watching the agonizingly 00:16:03.850 --> 00:16:06.509 slow dimmer switch of a South Pole foreglow and 00:16:06.509 --> 00:16:09.149 a six -month night, completely dictates how you 00:16:09.070 --> 00:16:11.590 experience those constant physics. The afterglow 00:16:11.590 --> 00:16:14.190 is just a beautifully complex, infinitely variable 00:16:14.190 --> 00:16:16.570 system. It really is. So here's our challenge 00:16:16.570 --> 00:16:18.809 to you. Tonight, after the sun goes down, don't 00:16:18.809 --> 00:16:20.929 just walk inside and flip on a lamp. Wait for 00:16:20.929 --> 00:16:23.090 it. Just wait a bit. Wait until you think the 00:16:23.090 --> 00:16:26.110 sun is roughly two to six degrees below the horizon. 00:16:26.889 --> 00:16:29.620 Look up. Look past the darkness and actively 00:16:29.620 --> 00:16:32.059 try to spot the structural overlap of the purple 00:16:32.059 --> 00:16:35.279 light Try to find that bright segment lingering 00:16:35.279 --> 00:16:37.139 right at the edge of the world before nautical 00:16:37.139 --> 00:16:39.340 twilight finally takes over look for the hidden 00:16:39.340 --> 00:16:42.399 machinery at work and As you look up at that 00:16:42.399 --> 00:16:44.720 glowing horizon tonight. I want to leave you 00:16:44.720 --> 00:16:48.259 with one final thought to ponder. Okay, we know 00:16:48.490 --> 00:16:51.889 that the incredibly fine natural volcanic dust 00:16:51.889 --> 00:16:55.470 from an eruption in 1883 drastically altered 00:16:55.470 --> 00:16:57.830 the colors of the afterglow, right? Creating 00:16:57.830 --> 00:16:59.730 skies so vivid they changed the course of art 00:16:59.730 --> 00:17:02.490 history. But think about the atmospheric soup 00:17:02.490 --> 00:17:05.529 hovering over us today. What kind of invisible 00:17:05.529 --> 00:17:08.509 modern particulates from global industrial emissions, 00:17:08.809 --> 00:17:11.009 constant commercial air travel, or the sprawling 00:17:11.009 --> 00:17:13.210 footprint of urban life are suspended up there 00:17:13.210 --> 00:17:15.670 right now, actively scattering the light in our 00:17:15.670 --> 00:17:18.500 skies? When you look at a brilliantly vivid, 00:17:18.779 --> 00:17:21.720 bruised purple sunset tonight, are you just seeing 00:17:21.720 --> 00:17:24.559 the natural, untouched physics of the atmosphere? 00:17:25.099 --> 00:17:27.519 Or are you actually seeing the invisible footprint 00:17:27.519 --> 00:17:30.259 of our modern world suspended in the air and 00:17:30.259 --> 00:17:33.019 illuminated in red and blue? That is a wild thought. 00:17:33.059 --> 00:17:34.839 It really makes you realize that the twilight 00:17:34.839 --> 00:17:37.140 sky was never just a simple off switch at the 00:17:37.140 --> 00:17:40.420 end of the day. It is a massive, complex, brilliantly 00:17:40.420 --> 00:17:43.380 illuminated mirror reflecting exactly what is 00:17:43.380 --> 00:17:45.279 suspended in our world. Thanks for joining us 00:17:45.279 --> 00:17:45.960 on the Steep Dive.