WEBVTT 00:00:07.098 --> 00:00:09.959 What if you could only see one color? 00:00:09.959 --> 00:00:11.584 Imagine, for instance, 00:00:11.584 --> 00:00:13.738 that you could only see things that were red 00:00:13.738 --> 00:00:14.869 and that everything else 00:00:14.869 --> 00:00:17.106 was completely invisible to you. 00:00:17.106 --> 00:00:18.139 As it turns out, 00:00:18.139 --> 00:00:20.414 that's how you live your life all the time 00:00:20.414 --> 00:00:21.919 because your eyes can only see 00:00:21.919 --> 00:00:25.084 a minuscule part of the full spectrum of light. 00:00:25.084 --> 00:00:28.183 Different kinds of light are all around you everyday 00:00:28.183 --> 00:00:30.101 but are invisible to the human eye, 00:00:30.101 --> 00:00:32.940 from the radio waves that carry your favorite songs, 00:00:32.940 --> 00:00:35.475 to the x-rays doctors use to see inside of you, 00:00:35.475 --> 00:00:37.939 to the microwaves that heat up your food. 00:00:38.554 --> 00:00:39.682 In order to understand 00:00:39.682 --> 00:00:41.243 how these can all be light, 00:00:41.243 --> 00:00:42.656 we'll need to know a thing or two 00:00:42.656 --> 00:00:44.284 about what light is. 00:00:44.284 --> 00:00:46.519 Light is electromagnetic radiation 00:00:46.519 --> 00:00:49.037 that acts like both a wave and a particle. 00:00:49.037 --> 00:00:52.028 Light waves are kind of like waves on the ocean. 00:00:52.028 --> 00:00:53.991 There are big waves and small waves, 00:00:53.991 --> 00:00:55.698 waves that crash on the shore 00:00:55.698 --> 00:00:57.235 one right after the other, 00:00:57.235 --> 00:01:00.155 and waves that only roll in every so often. 00:01:00.155 --> 00:01:02.992 The size of a wave is called its wavelength, 00:01:02.992 --> 00:01:04.498 and how often it comes by 00:01:04.498 --> 00:01:06.393 is called its frequency. 00:01:06.793 --> 00:01:08.748 Imagine being a boat in that ocean, 00:01:08.748 --> 00:01:11.231 bobbing up and down as the waves go by. 00:01:11.231 --> 00:01:13.667 If the waves that day have long wavelengths, 00:01:13.667 --> 00:01:15.789 they'll make you bob only so often, 00:01:15.789 --> 00:01:17.696 or at a low frequency. 00:01:17.696 --> 00:01:20.058 If the waves, instead, have short wavelengths, 00:01:20.058 --> 00:01:21.308 they'll be close together, 00:01:21.308 --> 00:01:23.535 and you'll bob up and down much more often, 00:01:23.535 --> 00:01:25.286 at a high frequency. 00:01:25.286 --> 00:01:27.902 Different kinds of light are all waves, 00:01:27.902 --> 00:01:30.406 they just have different wavelengths and frequencies. 00:01:31.298 --> 00:01:33.195 If you know the wavelength or frequency 00:01:33.195 --> 00:01:34.323 of a wave of light, 00:01:34.323 --> 00:01:36.787 you can also figure out its energy. 00:01:36.787 --> 00:01:39.002 Long wavelengths have low energies, 00:01:39.002 --> 00:01:41.230 while short wavelengths have high energies. 00:01:41.230 --> 00:01:42.673 It's easy to remember 00:01:42.673 --> 00:01:44.727 if you think about being in that boat. 00:01:44.727 --> 00:01:46.428 If you were out sailing on a day 00:01:46.428 --> 00:01:47.975 with short, choppy waves, 00:01:47.975 --> 00:01:50.398 you'd probably be pretty high energy yourself, 00:01:50.398 --> 00:01:53.650 running around to keep things from falling over. 00:01:53.650 --> 00:01:54.805 But on a long wavelength sea, 00:01:54.805 --> 00:01:57.058 you'd be rolling along, relaxed, 00:01:57.058 --> 00:01:58.312 low energy. 00:01:59.158 --> 00:02:00.704 The energy of light tells us 00:02:00.704 --> 00:02:02.635 how it will interact with matter, 00:02:02.635 --> 00:02:04.918 for example, the cells of our eyes. 00:02:04.918 --> 00:02:07.630 When we see, it's because the energy of light 00:02:07.630 --> 00:02:09.590 stimulates a receptor in our eye 00:02:09.590 --> 00:02:11.324 called the retina. 00:02:11.324 --> 00:02:13.117 Our retina are only sensitive to light 00:02:13.117 --> 00:02:15.319 with a very small range in energy, 00:02:15.319 --> 00:02:18.484 and so we call that range of light visible light. 00:02:18.484 --> 00:02:20.700 Inside our retina are special receptors 00:02:20.700 --> 00:02:22.734 called rods and cones. 00:02:22.734 --> 00:02:24.570 The rods measure brightness, 00:02:24.570 --> 00:02:26.538 so we know how much light there is. 00:02:26.538 --> 00:02:29.552 The cones are in charge of what color of light we see 00:02:29.552 --> 00:02:31.221 because different cones are sensitive 00:02:31.221 --> 00:02:33.426 to different energies of light. 00:02:33.426 --> 00:02:35.421 Some cones are more excited by light 00:02:35.421 --> 00:02:37.820 that is long wavelength and low energy, 00:02:37.820 --> 00:02:39.654 and other cones are more excited 00:02:39.654 --> 00:02:42.537 by short wavelength, high-energy light. 00:02:42.537 --> 00:02:43.767 When light hits our eye, 00:02:43.767 --> 00:02:46.183 the relative amount of energy each cone measures 00:02:46.183 --> 00:02:48.981 signals our brain to perceive colors. 00:02:48.981 --> 00:02:50.235 The rainbow we perceive 00:02:50.235 --> 00:02:53.621 is actually visible light in order of its energy. 00:02:53.621 --> 00:02:54.693 At one side of the rainbow 00:02:54.693 --> 00:02:57.397 is low-energy light we see as red, 00:02:57.397 --> 00:02:59.734 and at the other side is high-energy light 00:02:59.734 --> 00:03:01.631 we see as blue. 00:03:01.631 --> 00:03:02.813 If light shines on us 00:03:02.813 --> 00:03:04.896 that has an energy our retina can't measure, 00:03:04.896 --> 00:03:06.784 we won't be able to see it. 00:03:07.600 --> 00:03:09.957 Light that is too short wavelength or high energy 00:03:09.957 --> 00:03:11.981 gets absorbed by the eye's surface 00:03:11.981 --> 00:03:14.130 before it can even get to the retina, 00:03:14.130 --> 00:03:16.940 and light that is too long wavelength 00:03:16.940 --> 00:03:17.206 doesn't have enough energy 00:03:17.206 --> 00:03:19.576 to stimulate our retina at all. 00:03:19.576 --> 00:03:21.520 The only thing that makes one kind of light 00:03:21.520 --> 00:03:24.270 different from another is its wavelength. 00:03:24.270 --> 00:03:26.215 Radio waves have long wavelengths, 00:03:26.215 --> 00:03:28.514 while x-rays have short wavelengths. 00:03:28.514 --> 00:03:30.975 And visible light, the kind you can actually see, 00:03:30.975 --> 00:03:33.149 is somewhere in between. 00:03:33.149 --> 00:03:35.210 Even though our eyes can't detect light 00:03:35.210 --> 00:03:37.029 outside of the visible range, 00:03:37.029 --> 00:03:38.662 we can build special detectors 00:03:38.662 --> 00:03:39.618 that are stimulated 00:03:39.618 --> 00:03:41.622 by these other wavelengths of light, 00:03:41.622 --> 00:03:43.464 kind of like digital eyes. 00:03:43.464 --> 00:03:44.639 With these devices, 00:03:44.639 --> 00:03:46.455 we can measure the light that is there, 00:03:46.455 --> 00:03:48.804 even though we can't see it ourselves. 00:03:50.264 --> 00:03:51.819 So, take a step back and think about 00:03:51.819 --> 00:03:53.789 all of this for a moment. 00:03:53.789 --> 00:03:54.875 Even though they seem different, 00:03:54.875 --> 00:03:57.092 the warmth you feel from a crackling fire 00:03:57.092 --> 00:03:58.972 is the same as the sun shining on you 00:03:58.972 --> 00:04:00.234 on a beautiful day, 00:04:00.234 --> 00:04:01.927 the same as ultraviolet light 00:04:01.927 --> 00:04:04.418 you put on sunscreen to protect yourself from, 00:04:04.418 --> 00:04:05.997 the same thing as your TV, 00:04:05.997 --> 00:04:06.897 your radio, 00:04:06.897 --> 00:04:08.280 and your microwave. 00:04:09.049 --> 00:04:11.479 Now, those examples are all things here on Earth, 00:04:11.479 --> 00:04:13.759 things you experience in your everyday life, 00:04:13.759 --> 00:04:16.594 but here's something even more amazing. 00:04:16.594 --> 00:04:20.121 Our universe gives off the full spectrum of light, too. 00:04:20.782 --> 00:04:22.459 When you think of the night sky, 00:04:22.459 --> 00:04:24.057 you probably think of being able 00:04:24.057 --> 00:04:26.677 to see the stars shining with your own eyes, 00:04:26.677 --> 00:04:28.312 but that's just visible light, 00:04:28.312 --> 00:04:30.181 which you now know is only a tiny part 00:04:30.181 --> 00:04:31.956 of the full spectrum. 00:04:31.956 --> 00:04:33.287 If we had to draw the universe 00:04:33.287 --> 00:04:35.600 and could only use visible light, 00:04:35.600 --> 00:04:37.428 it would be like having only one crayon -- 00:04:37.428 --> 00:04:38.702 pretty sad. 00:04:39.426 --> 00:04:41.504 To see the universe in its full spectrum, 00:04:41.504 --> 00:04:43.329 we need to have the right eyes, 00:04:43.329 --> 00:04:45.283 and that means using special telescopes 00:04:45.283 --> 00:04:48.158 that can help us see beyond visible light. 00:04:48.158 --> 00:04:50.498 You've probably heard of the Hubble Space Telescope 00:04:50.498 --> 00:04:51.783 and seen its beautiful pictures 00:04:51.783 --> 00:04:54.516 taken in visible and ultraviolet light. 00:04:54.516 --> 00:04:55.749 But you might not know 00:04:55.749 --> 00:04:58.355 that there are 20 space telescopes in orbit, 00:04:58.355 --> 00:05:00.144 missions that can each see part 00:05:00.144 --> 00:05:01.780 of the full spectrum of light. 00:05:02.379 --> 00:05:04.862 With telescopes acting as our virtual eyes, 00:05:04.862 --> 00:05:06.610 both in space and here on Earth, 00:05:06.610 --> 00:05:09.260 we can see some amazing things. 00:05:09.260 --> 00:05:10.787 And the coolest thing of all, 00:05:10.787 --> 00:05:13.201 no matter the wavelength or energy, 00:05:13.201 --> 00:05:15.697 the light that we see out in the distant universe 00:05:15.697 --> 00:05:17.120 is the same thing as the light 00:05:17.120 --> 00:05:19.717 that we can experience and study here on Earth. 00:05:19.717 --> 00:05:20.992 So, since we know the physics 00:05:20.992 --> 00:05:22.280 of how x-ray, 00:05:22.280 --> 00:05:23.410 ultraviolet light, 00:05:23.410 --> 00:05:25.204 or microwaves work here, 00:05:25.204 --> 00:05:28.202 we can study the light of a distant star or galaxy 00:05:28.202 --> 00:05:29.698 and know what kinds of things 00:05:29.698 --> 00:05:31.503 are happening there too. 00:05:31.503 --> 00:05:33.254 So, as you go about your daily life, 00:05:33.254 --> 00:05:35.954 think beyond what your eyes can and can't see. 00:05:35.954 --> 00:05:38.371 Knowing just a little bit about the natural world 00:05:38.371 --> 00:05:40.347 can help you perceive the full spectrum 00:05:40.347 --> 00:05:42.253 around you all the time.