1 00:00:00,000 --> 00:00:05,000 Hi, kids. I'm Peter Poluski at NASA Ames Research Center. 2 00:00:05,000 --> 00:00:07,000 I study light in the Earth's atmosphere. 3 00:00:07,000 --> 00:00:08,000 What can I do for you today? 4 00:00:08,000 --> 00:00:10,000 We're trying to figure out a problem, 5 00:00:10,000 --> 00:00:13,000 and we need to know why the skies are blue during the day. 6 00:00:13,000 --> 00:00:15,000 Good question. 7 00:00:15,000 --> 00:00:17,000 Let me first talk to you about the sun. 8 00:00:17,000 --> 00:00:20,000 It's a white light, which means it's really a mixture 9 00:00:20,000 --> 00:00:23,000 of all colors of the spectrum, from blue to red. 10 00:00:23,000 --> 00:00:26,000 If the sunlight is white, then why is the sky blue? 11 00:00:26,000 --> 00:00:28,000 We learned about reflection at the Jefferson Lab. 12 00:00:28,000 --> 00:00:32,000 Could the sky be blue because it's reflecting blue off the ocean? 13 00:00:32,000 --> 00:00:34,000 No, that's a common misconception. 14 00:00:34,000 --> 00:00:36,000 The Earth has an atmosphere, 15 00:00:36,000 --> 00:00:39,000 which is made up of molecules such as oxygen and nitrogen. 16 00:00:39,000 --> 00:00:42,000 It's also made up of tiny little microscopic particles, 17 00:00:42,000 --> 00:00:45,000 and these tiny little microscopic particles in the atmosphere 18 00:00:45,000 --> 00:00:46,000 are called aerosols. 19 00:00:46,000 --> 00:00:48,000 I don't see anything in the air. 20 00:00:48,000 --> 00:00:51,000 Well, let me ask you first, what do you know about light? 21 00:00:51,000 --> 00:00:53,000 We learned at the Boston Museum of Science 22 00:00:53,000 --> 00:00:56,000 that light is a wave and that it is made up of photons. 23 00:00:56,000 --> 00:00:59,000 Occasionally, the photons will actually bounce off of the molecules 24 00:00:59,000 --> 00:01:02,000 and particles and go off into different directions. 25 00:01:02,000 --> 00:01:04,000 That's something that we call scattering. 26 00:01:04,000 --> 00:01:07,000 Let me show you an experiment I have set up here. 27 00:01:08,000 --> 00:01:11,000 This fancy instrument is something we call a sun simulator, 28 00:01:11,000 --> 00:01:15,000 but really it's just a lamp which sort of mimics the output of the sun. 29 00:01:16,000 --> 00:01:19,000 First of all, you can see the beaker here 30 00:01:19,000 --> 00:01:22,000 has very little light scattering out of the sides of it. 31 00:01:22,000 --> 00:01:25,000 Now watch what happens when I add some milk to the beaker. 32 00:01:25,000 --> 00:01:27,000 What does the milk represent? 33 00:01:27,000 --> 00:01:30,000 The molecules and particles in the atmosphere. 34 00:01:30,000 --> 00:01:32,000 Now we've got plenty of light scattered out the sides, 35 00:01:32,000 --> 00:01:34,000 and notice it's very bluish. 36 00:01:34,000 --> 00:01:38,000 When we look at the sunbeam that's been transmitted through the beaker, however, 37 00:01:38,000 --> 00:01:39,000 that's become red. 38 00:01:39,000 --> 00:01:41,000 That's because the blue light's been removed from the beam 39 00:01:41,000 --> 00:01:43,000 and scattered out the sides. 40 00:01:43,000 --> 00:01:46,000 Just like the sky looks blue, but I don't understand. 41 00:01:46,000 --> 00:01:49,000 Remember we said that sunlight is a mixture of all colors. 42 00:01:49,000 --> 00:01:52,000 Now the blue photons will actually scatter off of the particles 43 00:01:52,000 --> 00:01:54,000 much more frequently than the red ones. 44 00:01:54,000 --> 00:01:57,000 That means that we get blue light scattered out 45 00:01:57,000 --> 00:01:59,000 and the red light gets transmitted through. 46 00:01:59,000 --> 00:02:03,000 So why do we see red skies at night and in the morning? 47 00:02:03,000 --> 00:02:05,000 Well, when the sun's near the horizon, 48 00:02:05,000 --> 00:02:08,000 the sunbeam is traveling through a very, very thick portion of the atmosphere. 49 00:02:08,000 --> 00:02:11,000 That's also where most of the particles are concentrated 50 00:02:11,000 --> 00:02:14,000 because gravity keeps the particles near the ground. 51 00:02:14,000 --> 00:02:15,000 That makes sense. 52 00:02:15,000 --> 00:02:18,000 Any event that puts more particles near the horizon 53 00:02:18,000 --> 00:02:21,000 can make the sunset and sunrise even more red than it is usually. 54 00:02:21,000 --> 00:02:24,000 Now, one of those events is a pollution event. 55 00:02:24,000 --> 00:02:27,000 I'm not an expert in pollution, but I happen to know one. 56 00:02:27,000 --> 00:02:30,000 His name is Mark, and he works at the Langley Research Center. 57 00:02:30,000 --> 00:02:32,000 So why don't we give him a call? 58 00:02:32,000 --> 00:02:34,000 This is so cool. 59 00:02:34,000 --> 00:02:37,000 Wow, looks like we found the right place. 60 00:02:37,000 --> 00:02:38,000 Hello, Mr. Vaughn. 61 00:02:38,000 --> 00:02:39,000 Hey, guys. 62 00:02:39,000 --> 00:02:42,000 Well, we need to know more about what causes air pollution. 63 00:02:42,000 --> 00:02:44,000 Mostly when we think about air pollution, 64 00:02:44,000 --> 00:02:47,000 we think about the things that human beings put into the air. 65 00:02:47,000 --> 00:02:50,000 We think about the emissions from factory smokestacks. 66 00:02:50,000 --> 00:02:53,000 They're thinking about the exhaust from automobiles. 67 00:02:53,000 --> 00:02:57,000 But when we actually get down to measuring the aerosol content in the air, 68 00:02:57,000 --> 00:03:01,000 we find out that human beings account for only about 10% of it. 69 00:03:01,000 --> 00:03:04,000 The other 90% comes from Mother Nature herself. 70 00:03:04,000 --> 00:03:06,000 Mother Nature? 71 00:03:06,000 --> 00:03:08,000 But I always thought that nature was clean and natural. 72 00:03:08,000 --> 00:03:10,000 Think about a volcano going off. 73 00:03:10,000 --> 00:03:12,000 It's not just lava that comes out of it. 74 00:03:12,000 --> 00:03:16,000 It also spits blistering hot gases way, way, way up. 75 00:03:16,000 --> 00:03:18,000 And those gases react with water vapor 76 00:03:18,000 --> 00:03:21,000 to form little tiny sulfuric acid droplets 77 00:03:21,000 --> 00:03:24,000 that can hang around in the stratosphere for years. 78 00:03:24,000 --> 00:03:27,000 Or think about big dust storms coming across the desert. 79 00:03:27,000 --> 00:03:30,000 How do you know how much dirt is in the air? 80 00:03:30,000 --> 00:03:34,000 Matthew, you'd be a cloud with a squirt bottle. 81 00:03:34,000 --> 00:03:37,000 PJ, you are going to be a lidar with a laser. 82 00:03:37,000 --> 00:03:41,000 And I'm going to stand here with my flower and be a dust storm. 83 00:03:43,000 --> 00:03:45,000 Wow, they look like sparkles. 84 00:03:45,000 --> 00:03:46,000 I bet they do. 85 00:03:46,000 --> 00:03:48,000 We use a very similar technique 86 00:03:48,000 --> 00:03:51,000 when we measure real aerosols in the atmosphere. 87 00:03:51,000 --> 00:03:54,000 Only then we use machines called a lidar. 88 00:03:54,000 --> 00:03:56,000 Come on, I've got one right over here I can show you. 89 00:04:00,000 --> 00:04:02,000 Wow, that's a big machine. 90 00:04:02,000 --> 00:04:03,000 What does it do? 91 00:04:03,000 --> 00:04:06,000 What we do is fire pulses of laser light 92 00:04:06,000 --> 00:04:08,000 out of the laser and right to this turning mirror here. 93 00:04:08,000 --> 00:04:11,000 From there, they shoot straight up into the atmosphere. 94 00:04:12,000 --> 00:04:16,000 Just like we saw the sparkles off of aerosols in our little experiment, 95 00:04:16,000 --> 00:04:19,000 we use our telescope to look at the sparkles 96 00:04:19,000 --> 00:04:22,000 off of real aerosols in the atmosphere. 97 00:04:22,000 --> 00:04:24,000 Could the aerosols from pollution 98 00:04:24,000 --> 00:04:27,000 cause the sky to turn red during sunrises and sunsets? 99 00:04:27,000 --> 00:04:30,000 Sure, sure they can. Circumstances are right. 100 00:04:30,000 --> 00:04:32,000 We learned from Dr. Poluski 101 00:04:32,000 --> 00:04:34,000 that aerosols scatter more blue photons 102 00:04:34,000 --> 00:04:36,000 and leave the red ones for us to see. 103 00:04:36,000 --> 00:04:37,000 Oh, absolutely. 104 00:04:37,000 --> 00:04:40,000 If you increase the number of small particles up there, 105 00:04:40,000 --> 00:04:42,000 they will scatter away more blue light 106 00:04:42,000 --> 00:04:44,000 and you will see more red. 107 00:04:44,000 --> 00:04:46,000 Thank you. We learned a lot. 108 00:04:46,000 --> 00:04:48,000 Good. Good luck on your project. 109 00:04:48,000 --> 00:04:49,000 Bye.