1 00:00:00,090 --> 00:00:02,490 The following content is provided under a Creative 2 00:00:02,490 --> 00:00:04,030 Commons license. 3 00:00:04,030 --> 00:00:06,330 Your support will help MIT OpenCourseWare 4 00:00:06,330 --> 00:00:10,690 continue to offer high quality educational resources for free. 5 00:00:10,690 --> 00:00:13,320 To make a donation or view additional materials 6 00:00:13,320 --> 00:00:17,280 from hundreds of MIT courses, visit MIT OpenCourseWare 7 00:00:17,280 --> 00:00:18,430 at ocw.mit.edu. 8 00:00:24,730 --> 00:00:27,040 MARK HARTMAN: Invisible light. 9 00:00:27,040 --> 00:00:29,480 And Steve, why do we call it invisible light? 10 00:00:29,480 --> 00:00:32,830 AUDIENCE: Because it cannot be detected by the human eye. 11 00:00:32,830 --> 00:00:34,460 MARK HARTMAN: It's invisible to us, 12 00:00:34,460 --> 00:00:36,080 but it's not that it's not there. 13 00:00:38,670 --> 00:00:51,300 So normally for photons of light a natural unit of energy-- 14 00:00:51,300 --> 00:00:54,390 we don't want to deal with stuff that's as big as a joule. 15 00:00:54,390 --> 00:00:57,240 A joule is a large amount of energy. 16 00:00:57,240 --> 00:01:02,825 We want to deal with one electron volt-- 17 00:01:05,400 --> 00:01:08,610 two separate words-- electron volt. 18 00:01:08,610 --> 00:01:11,940 That is actually equal to 1.6 times 10 19 00:01:11,940 --> 00:01:15,025 to the minus 19th joules. 20 00:01:18,940 --> 00:01:21,460 So is an electron volt a large amount of energy 21 00:01:21,460 --> 00:01:23,850 or a small amount of energy? 22 00:01:23,850 --> 00:01:24,717 AUDIENCE: Small. 23 00:01:24,717 --> 00:01:26,050 MARK HARTMAN: What's that, Juan? 24 00:01:26,050 --> 00:01:27,010 I couldn't quite hear you. 25 00:01:27,010 --> 00:01:27,676 AUDIENCE: Small. 26 00:01:27,676 --> 00:01:30,760 MARK HARTMAN: It is a small amount of energy. 27 00:01:30,760 --> 00:01:34,900 1 electron volt is actually the amount of energy 28 00:01:34,900 --> 00:01:39,010 that it takes to move an electron around a circuit 29 00:01:39,010 --> 00:01:41,050 from one side of a battery to another 30 00:01:41,050 --> 00:01:43,280 if you have a 1 volt battery. 31 00:01:43,280 --> 00:01:46,490 So it's not a very large amount of energy, 32 00:01:46,490 --> 00:01:51,910 but then again, photons are streaming out of light sources 33 00:01:51,910 --> 00:01:53,570 all the time. 34 00:01:53,570 --> 00:01:56,570 So each photon can carry a small amount of energy. 35 00:01:56,570 --> 00:01:59,110 Let's look at how much energy each one 36 00:01:59,110 --> 00:02:02,110 of these different kinds of photons can produce, 37 00:02:02,110 --> 00:02:04,840 because we've got on our chart here gamma ray 38 00:02:04,840 --> 00:02:08,750 light, x-ray light, ultraviolet light, visible light, 39 00:02:08,750 --> 00:02:12,400 infrared light, microwave light, and radio light. 40 00:02:12,400 --> 00:02:14,800 Let's start at visible light. 41 00:02:14,800 --> 00:02:19,120 I'm going to leave this chart up for a little bit of reference 42 00:02:19,120 --> 00:02:20,320 for us. 43 00:02:20,320 --> 00:02:22,780 Visible light is typically each photon 44 00:02:22,780 --> 00:02:27,740 is somewhere between 2 electron volts and 3 electron volts. 45 00:02:27,740 --> 00:02:37,030 So we're just going to say visible light is about 2 46 00:02:37,030 --> 00:02:40,810 to 3 electron volts, and this is the way that we 47 00:02:40,810 --> 00:02:42,370 write electron volts. 48 00:02:42,370 --> 00:02:46,420 We write it as a lowercase e and a capital V. 49 00:02:46,420 --> 00:02:48,280 So each photon of energy-- 50 00:02:48,280 --> 00:02:52,120 somewhere between 2 and 3 electron volts. 51 00:02:52,120 --> 00:02:53,560 What would you predict-- 52 00:02:53,560 --> 00:02:55,390 knowing what you know about light, 53 00:02:55,390 --> 00:02:58,620 what would be the energy of a photon that we would record-- 54 00:02:58,620 --> 00:03:02,550 or that we would experience as red? 55 00:03:02,550 --> 00:03:07,190 Would it be closer to 2 electron volts or 3 electron volts? 56 00:03:07,190 --> 00:03:07,730 AUDIENCE: 2. 57 00:03:07,730 --> 00:03:08,230 AUDIENCE: 2. 58 00:03:08,230 --> 00:03:08,896 MARK HARTMAN: 2. 59 00:03:08,896 --> 00:03:10,900 Why 2, Chris? 60 00:03:10,900 --> 00:03:13,090 AUDIENCE: Because red is low. 61 00:03:13,090 --> 00:03:18,680 MARK HARTMAN: Low energy photons we experience as red. 62 00:03:18,680 --> 00:03:26,950 So red photons are down here at around 2 electron volts. 63 00:03:26,950 --> 00:03:31,780 Blue photons around 3 electron volts, and I'm rounding off. 64 00:03:31,780 --> 00:03:35,810 I don't know exactly what it is, but it's around there. 65 00:03:35,810 --> 00:03:37,960 So what do you think is going to be 66 00:03:37,960 --> 00:03:42,370 true about the energy of ultraviolet photons? 67 00:03:42,370 --> 00:03:44,680 Is it going to be larger than 3, or is it 68 00:03:44,680 --> 00:03:46,700 going to be less than 2 electron volts? 69 00:03:46,700 --> 00:03:47,572 AUDIENCE: Large. 70 00:03:47,572 --> 00:03:48,988 AUDIENCE: It's going to be larger. 71 00:03:48,988 --> 00:03:50,620 MARK HARTMAN: It's going to be larger. 72 00:03:50,620 --> 00:03:53,690 If we look here, we have a listing-- ultraviolet 73 00:03:53,690 --> 00:03:57,280 is somewhere between 3 electron volts and 10 74 00:03:57,280 --> 00:04:00,620 to the power of 3 electron volts, 75 00:04:00,620 --> 00:04:05,420 so 3 electron volts up to 1,000 electron volts. 76 00:04:05,420 --> 00:04:08,590 So there's actually a pretty wide range of photon energies 77 00:04:08,590 --> 00:04:10,811 that we can deal with. 78 00:04:10,811 --> 00:04:12,560 And you don't have to write that one down. 79 00:04:12,560 --> 00:04:13,643 That's just as an example. 80 00:04:13,643 --> 00:04:16,120 What about radio light? 81 00:04:16,120 --> 00:04:20,440 Radio light is very, very low energy light. 82 00:04:20,440 --> 00:04:21,910 It has photons. 83 00:04:21,910 --> 00:04:27,880 Each photon carries less than 10 to the minus sixth electron 84 00:04:27,880 --> 00:04:32,530 volts, so 1 millionth of the light 85 00:04:32,530 --> 00:04:35,400 that a visible light photon carries. 86 00:04:35,400 --> 00:04:38,710 So a lot of you asked in your reflections yesterday, 87 00:04:38,710 --> 00:04:41,410 why can't we just have one mega telescope 88 00:04:41,410 --> 00:04:45,530 that can be sensitive to all the different kinds of light? 89 00:04:45,530 --> 00:04:47,780 Well, the problem is you have to be sensitive to very, 90 00:04:47,780 --> 00:04:53,290 very low energy photons, as well as if we look at x-ray 91 00:04:53,290 --> 00:04:55,420 photons-- 92 00:04:55,420 --> 00:04:58,360 this is the other one that's important to us. 93 00:04:58,360 --> 00:05:04,780 X-ray photons have an energy between 1,000 electron volts 94 00:05:04,780 --> 00:05:08,450 and 100,000 electron volts. 95 00:05:08,450 --> 00:05:13,690 So we're going to say x-rays go from 1,000 96 00:05:13,690 --> 00:05:18,310 to 100,000 electron volts. 97 00:05:18,310 --> 00:05:21,340 I want you to rewrite these two numbers as scientific notation 98 00:05:21,340 --> 00:05:22,720 underneath that in your notes. 99 00:05:22,720 --> 00:05:25,172 Just real quick, how would you rewrite 100 00:05:25,172 --> 00:05:26,380 those as scientific notation? 101 00:05:30,452 --> 00:05:32,160 Just write it in your notes, and then I'm 102 00:05:32,160 --> 00:05:34,130 going to ask somebody to share. 103 00:05:34,130 --> 00:05:35,610 Just a little bit of extra practice 104 00:05:35,610 --> 00:05:36,651 with scientific notation. 105 00:05:40,910 --> 00:05:46,585 So how do we write 1,000 as scientific notation, Peter? 106 00:05:46,585 --> 00:05:51,555 AUDIENCE: Either 10 to the third of 1 times 10 to the fourth. 107 00:05:51,555 --> 00:05:52,930 MARK HARTMAN: Let's look at that. 108 00:05:52,930 --> 00:05:58,570 So 10 to the third, or 1 times 10 to the fourth. 109 00:05:58,570 --> 00:05:59,723 What do you guys think? 110 00:05:59,723 --> 00:06:00,264 AUDIENCE: No. 111 00:06:00,264 --> 00:06:01,210 AUDIENCE: No. 112 00:06:01,210 --> 00:06:01,918 MARK HARTMAN: No. 113 00:06:01,918 --> 00:06:04,730 Why not, Nicki? 114 00:06:04,730 --> 00:06:08,767 AUDIENCE: I say 1 times 10 to the third power. 115 00:06:08,767 --> 00:06:10,350 MARK HARTMAN: Remember, by putting a 1 116 00:06:10,350 --> 00:06:12,690 in front of something, you just multiply-- 117 00:06:12,690 --> 00:06:15,310 you don't change the number after it. 118 00:06:15,310 --> 00:06:21,330 So you can write this as 10 to the power of 3 or 1 times 10 119 00:06:21,330 --> 00:06:24,720 to the power of 3, but it's not equal to 1 times 10 120 00:06:24,720 --> 00:06:26,340 to the power of 4. 121 00:06:26,340 --> 00:06:29,999 If you had 10 times 10 to the power of 4, that would be-- 122 00:06:29,999 --> 00:06:30,540 or I'm sorry. 123 00:06:30,540 --> 00:06:32,850 If you had 10 times 10 to the power of 3, 124 00:06:32,850 --> 00:06:34,800 that would be 10 to the power 4. 125 00:06:34,800 --> 00:06:41,160 So let's rewrite this 1,000 as 1 times 10 to the power of 3. 126 00:06:41,160 --> 00:06:42,680 What about 100,000? 127 00:06:42,680 --> 00:06:43,667 Azeith? 128 00:06:43,667 --> 00:06:46,110 AUDIENCE: 10 to the fifth. 129 00:06:46,110 --> 00:06:52,900 MARK HARTMAN: 1 times 10 to the fifth eV, or electron volts. 130 00:06:52,900 --> 00:06:54,510 So we can rewrite our range that way. 131 00:06:57,140 --> 00:07:00,570 So what we see here is that we've 132 00:07:00,570 --> 00:07:03,840 got a really wide range of photon energies. 133 00:07:03,840 --> 00:07:07,470 Now, we also have listed under here wavelength, 134 00:07:07,470 --> 00:07:09,930 and we're not going to worry too much about that, 135 00:07:09,930 --> 00:07:12,660 but we know that high energy photons 136 00:07:12,660 --> 00:07:15,210 can be thought of as having a short wavelength. 137 00:07:15,210 --> 00:07:19,210 Low energy light can have a very long wavelength, 138 00:07:19,210 --> 00:07:22,904 but you'll see there's a bunch of different telescopes here. 139 00:07:22,904 --> 00:07:25,320 We are going to be interested in-- we've already used data 140 00:07:25,320 --> 00:07:28,080 from the Hubble Space Telescope, which 141 00:07:28,080 --> 00:07:30,330 is sensitive to visible light. 142 00:07:30,330 --> 00:07:32,220 The Chandra X-ray Observatory, which 143 00:07:32,220 --> 00:07:36,270 you read about this morning, is sensitive to x-ray light. 144 00:07:36,270 --> 00:07:37,980 We've got these other things, too. 145 00:07:37,980 --> 00:07:40,770 There was a satellite that was up about a decade ago 146 00:07:40,770 --> 00:07:43,530 called The Compton Gamma Ray Observatory. 147 00:07:43,530 --> 00:07:47,220 It was in space, and it looked at gamma rays. 148 00:07:47,220 --> 00:07:49,890 There's also a thing that got decommissioned shortly a little 149 00:07:49,890 --> 00:07:54,900 while ago called the Extreme Ultraviolet Explorer, or EUVE. 150 00:07:54,900 --> 00:07:57,970 It looked at ultraviolet light. 151 00:07:57,970 --> 00:08:01,140 There's the most recent of the large telescopes 152 00:08:01,140 --> 00:08:03,390 that NASA has put into outer space. 153 00:08:03,390 --> 00:08:05,490 All of these are space based telescopes. 154 00:08:05,490 --> 00:08:07,380 They're satellites. 155 00:08:07,380 --> 00:08:11,880 The Spitzer Space Telescope looks at infrared light, 156 00:08:11,880 --> 00:08:14,250 and there's also-- 157 00:08:14,250 --> 00:08:18,380 there's an older satellite that is now done-- 158 00:08:18,380 --> 00:08:20,640 its useful life is over-- 159 00:08:20,640 --> 00:08:24,240 called the CoBE satellite-- and it looked at micro-wave, 160 00:08:24,240 --> 00:08:28,110 but then there's a bunch of dishes here on earth-- 161 00:08:28,110 --> 00:08:29,640 actually in South America-- 162 00:08:29,640 --> 00:08:33,210 called ALMA, and it looks at radio light. 163 00:08:33,210 --> 00:08:34,830 So there are different telescopes 164 00:08:34,830 --> 00:08:37,799 that look at these different energy ranges. 165 00:08:37,799 --> 00:08:39,669 So Shakib, do we have our-- 166 00:08:43,740 --> 00:08:56,710 True color images let's say in visible light and x-ray light. 167 00:09:10,150 --> 00:09:13,780 Now, the process by which we make a true color image 168 00:09:13,780 --> 00:09:15,670 is the same thing that we did yesterday. 169 00:09:15,670 --> 00:09:16,570 So what I'm going to do is I'm going 170 00:09:16,570 --> 00:09:18,670 to draw a little diagram that kind of takes us 171 00:09:18,670 --> 00:09:24,070 through the process for what we did yesterday, and then also-- 172 00:09:24,070 --> 00:09:25,712 can we not have that in the way? 173 00:09:25,712 --> 00:09:27,670 AUDIENCE: [INAUDIBLE]. 174 00:09:27,670 --> 00:09:29,237 MARK HARTMAN: So if people-- 175 00:09:29,237 --> 00:09:31,570 I'm not sure what's going on with the screen over there. 176 00:09:34,910 --> 00:09:37,480 We're going to diagram out the process of how 177 00:09:37,480 --> 00:09:40,600 you make a true color image in both visible light 178 00:09:40,600 --> 00:09:41,290 and x-ray light. 179 00:09:41,290 --> 00:09:43,748 So the first thing we're going to look at is visible light. 180 00:09:46,060 --> 00:09:48,730 This is yesterday when we used the filters. 181 00:09:48,730 --> 00:09:51,670 We use filters to help us filter out 182 00:09:51,670 --> 00:09:56,260 only photons of a certain energy. 183 00:09:56,260 --> 00:09:58,390 So I'm going to draw-- 184 00:09:58,390 --> 00:10:00,280 you want to leave space across your page 185 00:10:00,280 --> 00:10:03,180 to have this whole diagram, so I'm going to draw. 186 00:10:03,180 --> 00:10:04,540 Here's our source. 187 00:10:04,540 --> 00:10:11,250 We looked at the Orion nebula, and then over here we 188 00:10:11,250 --> 00:10:21,010 had our telescope, and then we had our detector on the back. 189 00:10:21,010 --> 00:10:24,180 So this is our telescope. 190 00:10:24,180 --> 00:10:25,275 This is our detector. 191 00:10:28,240 --> 00:10:30,880 And what we did was we put a filter 192 00:10:30,880 --> 00:10:36,680 in front of the telescope in front of the detector. 193 00:10:36,680 --> 00:10:39,200 So this was a filter. 194 00:10:39,200 --> 00:10:40,720 And what does the filter do? 195 00:10:40,720 --> 00:10:46,800 The filter only lets through a certain energy of light, 196 00:10:46,800 --> 00:10:48,700 a certain range of energies. 197 00:10:48,700 --> 00:10:53,050 So red photons, which are around 2 electron 198 00:10:53,050 --> 00:10:56,350 volts-- a red filter will only let those photons through. 199 00:10:56,350 --> 00:11:00,640 A green filter will only let through green photons. 200 00:11:00,640 --> 00:11:04,060 So what we have is-- 201 00:11:04,060 --> 00:11:06,800 I guess I don't have any colored markers, 202 00:11:06,800 --> 00:11:09,190 but we have from each point on the Orion 203 00:11:09,190 --> 00:11:14,140 nebula there are photons that are being produced and sent 204 00:11:14,140 --> 00:11:16,400 out, again, in all directions. 205 00:11:16,400 --> 00:11:18,520 We only collect some of them. 206 00:11:18,520 --> 00:11:21,490 We only collect the photons that actually 207 00:11:21,490 --> 00:11:26,190 get through the filter. 208 00:11:26,190 --> 00:11:35,560 Some of them stop if it's the wrong color, 209 00:11:35,560 --> 00:11:38,710 and then some of them go through. 210 00:11:38,710 --> 00:11:40,290 So this is the filter color. 211 00:11:45,380 --> 00:11:47,640 So the filter colors get through, 212 00:11:47,640 --> 00:11:49,840 and then they hit the detector. 213 00:11:49,840 --> 00:11:53,850 And so some of our photons end up 214 00:11:53,850 --> 00:11:56,715 in the different pixels of the detector. 215 00:11:59,250 --> 00:12:00,990 Now, after that, I'm just going to draw 216 00:12:00,990 --> 00:12:03,090 a line from the detector from the telescope. 217 00:12:03,090 --> 00:12:06,160 That's where we get our images. 218 00:12:06,160 --> 00:12:10,730 So I'm just going to go on to the next line, 219 00:12:10,730 --> 00:12:13,100 and we're going to get three images. 220 00:12:13,100 --> 00:12:16,850 We've got a red filtered image, a green filtered image, 221 00:12:16,850 --> 00:12:18,710 and a blue filtered image. 222 00:12:18,710 --> 00:12:36,787 So this is red filtered image, green, and blue. 223 00:12:42,780 --> 00:12:45,060 We have to take three separate pictures 224 00:12:45,060 --> 00:12:49,050 because we have to put three different filters in front. 225 00:12:49,050 --> 00:12:53,340 So first we take an exposure that has a red filter in front. 226 00:12:53,340 --> 00:12:55,480 Then we take an exposure-- or another image that 227 00:12:55,480 --> 00:12:56,730 has the green filter in front. 228 00:12:56,730 --> 00:13:00,370 Then we take another image that has the blue filter in front. 229 00:13:00,370 --> 00:13:06,030 So we use the filters to help us find out energy information, 230 00:13:06,030 --> 00:13:11,420 because from our images, the only information that we 231 00:13:11,420 --> 00:13:15,150 have is we have the number of photons. 232 00:13:18,930 --> 00:13:21,170 So the info in each of those images-- 233 00:13:21,170 --> 00:13:32,170 the number of photons at each position on the detector. 234 00:13:32,170 --> 00:13:34,750 So we only get the number of photons. 235 00:13:34,750 --> 00:13:38,890 When we looked at the images before we put them into the RGB 236 00:13:38,890 --> 00:13:42,670 frame, we were just saying, oh, there 237 00:13:42,670 --> 00:13:46,810 were five counts in this pixel, and there were three counts 238 00:13:46,810 --> 00:13:48,805 or 100 counts in another pixel. 239 00:13:48,805 --> 00:13:50,680 So the only information we have is the number 240 00:13:50,680 --> 00:13:52,700 of photons at each position. 241 00:13:52,700 --> 00:13:55,064 The color information, or the energy information, 242 00:13:55,064 --> 00:13:55,980 comes from the filter. 243 00:13:59,350 --> 00:14:04,840 So we get energy information from the filter. 244 00:14:08,690 --> 00:14:10,930 So now that we have these three images, 245 00:14:10,930 --> 00:14:16,250 we take those three images, and we put them into the computer. 246 00:14:16,250 --> 00:14:18,840 Here's our little computer. 247 00:14:18,840 --> 00:14:24,490 There's our little keyboard, and we put it into the DS9 image 248 00:14:24,490 --> 00:14:25,765 processing software. 249 00:14:34,460 --> 00:14:36,020 Image processing means that we can 250 00:14:36,020 --> 00:14:44,090 change how we display the image so that we can then 251 00:14:44,090 --> 00:14:48,830 combine the images using this image processing software 252 00:14:48,830 --> 00:14:51,485 into one true color image. 253 00:14:57,890 --> 00:15:02,600 And we say it's true color because when we have 254 00:15:02,600 --> 00:15:04,560 different colors in the image-- 255 00:15:04,560 --> 00:15:06,680 here's our image of the Orion nebula. 256 00:15:06,680 --> 00:15:09,750 Can somebody toss me a red marker? 257 00:15:09,750 --> 00:15:12,324 Anybody see one? 258 00:15:12,324 --> 00:15:14,290 Just throw it. 259 00:15:14,290 --> 00:15:14,790 Missed it. 260 00:15:18,020 --> 00:15:19,490 So the Orion nebula we saw. 261 00:15:19,490 --> 00:15:20,457 It was mostly red. 262 00:15:20,457 --> 00:15:22,790 There was a little bit of green and a little bit of blue 263 00:15:22,790 --> 00:15:23,480 there, as well. 264 00:15:27,700 --> 00:15:30,490 And when we say true color image, 265 00:15:30,490 --> 00:15:41,080 we mean an image where the color represents energy 266 00:15:41,080 --> 00:15:45,880 because we got the energy information from the filter. 267 00:15:45,880 --> 00:15:48,640 So when something looks red in a true color image, 268 00:15:48,640 --> 00:15:51,640 that's because it actually would look red to your eyes 269 00:15:51,640 --> 00:15:54,790 if you were out there in space looking at it, because it 270 00:15:54,790 --> 00:15:56,289 has higher energy photons-- 271 00:15:56,289 --> 00:15:56,830 or I'm sorry. 272 00:15:56,830 --> 00:16:00,910 It has lower energy photons that you've collected. 273 00:16:00,910 --> 00:16:05,380 So now what I want to do is to talk 274 00:16:05,380 --> 00:16:09,840 about how we make a true color image in x-ray light. 275 00:16:13,810 --> 00:16:15,644 I'm going to go through this kind of quickly 276 00:16:15,644 --> 00:16:18,184 because you guys are then going to go through it on your own, 277 00:16:18,184 --> 00:16:20,520 and we're going to have you create your own true color 278 00:16:20,520 --> 00:16:23,010 image in x-ray light. 279 00:16:23,010 --> 00:16:29,620 So in this case, we still have the Orion nebula, 280 00:16:29,620 --> 00:16:33,180 but instead of giving off visible light photons, 281 00:16:33,180 --> 00:16:35,560 we're going to have it give off x-ray light photons. 282 00:16:35,560 --> 00:16:38,440 And I'm going to represent x-ray light photons with a little x. 283 00:16:43,350 --> 00:16:45,750 Except when we looked at the Orion nebula, 284 00:16:45,750 --> 00:16:49,461 did it look like a cloud when we looked at it in x-rays? 285 00:16:49,461 --> 00:16:51,162 What did it look like? 286 00:16:51,162 --> 00:16:51,828 AUDIENCE: Light. 287 00:16:54,378 --> 00:16:55,425 AUDIENCE: [INAUDIBLE]. 288 00:16:55,425 --> 00:16:56,925 MARK HARTMAN: What did it look like? 289 00:16:56,925 --> 00:16:57,870 AUDIENCE: A bunch of stars. 290 00:16:57,870 --> 00:16:59,070 MARK HARTMAN: A bunch of stars. 291 00:16:59,070 --> 00:16:59,940 AUDIENCE: A bunch of stars. 292 00:16:59,940 --> 00:17:01,231 MARK HARTMAN: A bunch of stars. 293 00:17:01,231 --> 00:17:03,900 It looked like a bunch of points, round dots. 294 00:17:03,900 --> 00:17:08,050 It didn't have all this weird kind of fuzzy stuff. 295 00:17:08,050 --> 00:17:12,050 So it's not the cloud. 296 00:17:12,050 --> 00:17:15,030 It's not the fuzzy stuff that's giving off the x-rays, 297 00:17:15,030 --> 00:17:24,704 but it's the actual stars that are giving off x-rays. 298 00:17:24,704 --> 00:17:26,579 And they're giving off x-rays that are moving 299 00:17:26,579 --> 00:17:27,810 outward in all directions. 300 00:17:37,740 --> 00:17:42,030 Now, again, now we have the Chandra telescope, 301 00:17:42,030 --> 00:17:44,640 and to make it look like Chandra we're going to put-- 302 00:17:44,640 --> 00:17:48,930 well, yeah, we'll put the little wings on it. 303 00:17:48,930 --> 00:17:50,530 So this is the Chandra telescope. 304 00:17:55,000 --> 00:18:00,190 And then we have again same kind of idea. 305 00:18:00,190 --> 00:18:04,890 We have a detector, except this detector 306 00:18:04,890 --> 00:18:05,920 is sensitive to x-rays. 307 00:18:09,750 --> 00:18:18,780 However, from this detector, we only get one image. 308 00:18:18,780 --> 00:18:23,010 We don't need filters in front of the Chandra telescope 309 00:18:23,010 --> 00:18:26,340 because this detector works differently. 310 00:18:26,340 --> 00:18:28,590 The x-rays still come in. 311 00:18:28,590 --> 00:18:30,240 Some of them miss. 312 00:18:30,240 --> 00:18:31,230 Some of them go in. 313 00:18:31,230 --> 00:18:34,240 The ones that go in are the ones we collect. 314 00:18:34,240 --> 00:18:37,860 So that's our flux, but at the detector, 315 00:18:37,860 --> 00:18:46,470 it still tells you in different pixels how many x-ray photons 316 00:18:46,470 --> 00:18:53,605 you get, but in the picture now, which kind of looks like this 317 00:18:53,605 --> 00:18:55,980 because it's a picture of that three dimensional thing up 318 00:18:55,980 --> 00:18:57,160 above-- 319 00:18:57,160 --> 00:19:02,100 now we get the number of photons, 320 00:19:02,100 --> 00:19:04,100 which is the same as in the visible light image. 321 00:19:04,100 --> 00:19:15,950 We get the number of photons at each position, 322 00:19:15,950 --> 00:19:17,360 but we also get-- 323 00:19:17,360 --> 00:19:22,530 and we get the energy of each photon. 324 00:19:29,080 --> 00:19:31,420 So in this case, our energy information 325 00:19:31,420 --> 00:19:35,020 is actually collected on the detector. 326 00:19:35,020 --> 00:19:37,630 Each time a photon hits the detector, 327 00:19:37,630 --> 00:19:41,410 Chandra says, OK, the photon hit right here on the detector, 328 00:19:41,410 --> 00:19:45,160 and it hit with an energy of 100 electron volts-- 329 00:19:45,160 --> 00:19:49,220 I'm sorry-- of, say, 2,000 electron volts. 330 00:19:49,220 --> 00:19:52,390 So the detector sits there. 331 00:19:52,390 --> 00:19:55,870 I got another x-ray photon, and it landed at this place 332 00:19:55,870 --> 00:20:00,910 on the detector, and it has an energy of 50,000 electron 333 00:20:00,910 --> 00:20:02,110 volts. 334 00:20:02,110 --> 00:20:05,440 And this process just goes on, and on, and on. 335 00:20:05,440 --> 00:20:07,570 So from this one image, we get the number 336 00:20:07,570 --> 00:20:11,050 of photons in each position and the energy of each photon. 337 00:20:11,050 --> 00:20:14,350 We take that-- just the one image. 338 00:20:14,350 --> 00:20:18,490 We go to our computer, which looks a little bit worse 339 00:20:18,490 --> 00:20:21,190 for wear than the first computer because I can't draw it 340 00:20:21,190 --> 00:20:23,720 as well. 341 00:20:23,720 --> 00:20:26,080 And we don't use DS9. 342 00:20:26,080 --> 00:20:35,730 We use the Chandra education tools. 343 00:20:35,730 --> 00:20:38,530 That's what we get to when we go to the virtual observatory, 344 00:20:38,530 --> 00:20:41,100 and we get those extra tools that we can pull up, 345 00:20:41,100 --> 00:20:42,630 that extra pull down. 346 00:20:42,630 --> 00:20:45,420 Using those Chandra education tools, 347 00:20:45,420 --> 00:20:55,180 we filter out the different energies in the computer. 348 00:20:55,180 --> 00:20:57,730 We don't have a special filter out front, 349 00:20:57,730 --> 00:21:00,880 because if we've recorded the energy of each photon, 350 00:21:00,880 --> 00:21:04,150 we can actually tell the computer, OK, now, computer, 351 00:21:04,150 --> 00:21:08,260 show me only the photons that have low energies-- say, 352 00:21:08,260 --> 00:21:15,080 between 1,000 electron volts and 2,000 electron volts. 353 00:21:15,080 --> 00:21:18,010 So we do the filtering because the energy information 354 00:21:18,010 --> 00:21:19,870 is already there. 355 00:21:19,870 --> 00:21:21,520 And what comes out-- 356 00:21:21,520 --> 00:21:33,230 we can get high energy image, which means the light-- 357 00:21:33,230 --> 00:21:37,590 the photons that we've collected there have high energies. 358 00:21:37,590 --> 00:21:40,150 So we're going to get a high energy image. 359 00:21:40,150 --> 00:21:42,095 We're going to get a medium energy image. 360 00:21:46,616 --> 00:21:50,195 And that means an image that has medium energy photons. 361 00:21:52,910 --> 00:21:55,760 We're actually going to use the range for the high energy 362 00:21:55,760 --> 00:21:56,360 photons. 363 00:21:56,360 --> 00:21:59,720 We're going to say 4,000 electron 364 00:21:59,720 --> 00:22:04,760 volts to 8,000 electron volts. 365 00:22:04,760 --> 00:22:10,130 For medium energy image, we're going to say 1,600 electron 366 00:22:10,130 --> 00:22:15,930 volts to 4,000 electron volts. 367 00:22:15,930 --> 00:22:28,320 And for low energy, that's going to be 300 electron volts 368 00:22:28,320 --> 00:22:33,520 up to 1,600 electron volts. 369 00:22:33,520 --> 00:22:37,330 Chandra is actually sensitive to a little bit lower 370 00:22:37,330 --> 00:22:40,160 than 1,000 electron volts. 371 00:22:40,160 --> 00:22:43,180 So just like that detector was a little bit sensitive 372 00:22:43,180 --> 00:22:47,080 to the infrared light, now we are 373 00:22:47,080 --> 00:22:49,330 going to separate out all the photons that 374 00:22:49,330 --> 00:22:50,590 are in these different ranges. 375 00:22:53,530 --> 00:22:56,440 So we've created the images afterwards. 376 00:22:56,440 --> 00:22:58,740 Again, we put them back into the computer, 377 00:22:58,740 --> 00:23:03,120 and we still use the DS9 image processing software 378 00:23:03,120 --> 00:23:08,121 to put the images together. 379 00:23:08,121 --> 00:23:12,300 So DS9 image processing-- 380 00:23:16,760 --> 00:23:17,885 again, here's the computer. 381 00:23:23,260 --> 00:23:29,570 And we put that together to make a true color image. 382 00:23:34,080 --> 00:23:35,780 Well, let me ask you this. 383 00:23:35,780 --> 00:23:41,050 What do we mean by x-ray color? 384 00:23:41,050 --> 00:23:44,600 Do x-rays have a red color or a blue color? 385 00:23:44,600 --> 00:23:46,070 AUDIENCE: No. 386 00:23:46,070 --> 00:23:47,260 MARK HARTMAN: Who said that? 387 00:23:47,260 --> 00:23:49,690 AUDIENCE: Me. 388 00:23:49,690 --> 00:23:51,565 MARK HARTMAN: So what color are x-rays? 389 00:23:51,565 --> 00:23:52,770 AUDIENCE: Black and white. 390 00:23:52,770 --> 00:23:54,020 MARK HARTMAN: Black and white. 391 00:23:54,020 --> 00:23:56,110 Well, that's right, because we can count 392 00:23:56,110 --> 00:23:59,020 the intensity of the photons. 393 00:23:59,020 --> 00:24:02,920 We can count the number that we've collected, the flux, 394 00:24:02,920 --> 00:24:06,730 but how do we represent this, Azeith? 395 00:24:06,730 --> 00:24:08,830 AUDIENCE: X-rays usually [INAUDIBLE].. 396 00:24:08,830 --> 00:24:10,038 MARK HARTMAN: Say that again. 397 00:24:10,038 --> 00:24:13,132 AUDIENCE: They say it's red, red, red, red color 398 00:24:13,132 --> 00:24:16,264 [INAUDIBLE]. 399 00:24:16,264 --> 00:24:18,180 MARK HARTMAN: So we can see it is a red color, 400 00:24:18,180 --> 00:24:22,270 but I thought red photons had an energy of 2 electron volts. 401 00:24:22,270 --> 00:24:24,460 Here we've got like 300 electron volts. 402 00:24:28,880 --> 00:24:30,110 Can we-- go ahead, Steve. 403 00:24:30,110 --> 00:24:32,300 AUDIENCE: Are they invisible? 404 00:24:32,300 --> 00:24:36,290 MARK HARTMAN: Those colors are invisible to us. 405 00:24:36,290 --> 00:24:38,510 This range of x-rays-- 406 00:24:38,510 --> 00:24:41,810 if we had x-ray eyes, we would experience it 407 00:24:41,810 --> 00:24:42,720 in a different way. 408 00:24:42,720 --> 00:24:44,810 Our mind would say, oh, this looks 409 00:24:44,810 --> 00:24:52,190 like banana, some new thing that we can't interpret. 410 00:24:52,190 --> 00:24:55,970 So x-ray colors don't mean anything to us 411 00:24:55,970 --> 00:24:58,430 because we can't see x-rays. 412 00:24:58,430 --> 00:25:02,750 We have no experience of what these would look like, 413 00:25:02,750 --> 00:25:06,410 but what we can do is we can make an analogy. 414 00:25:06,410 --> 00:25:09,530 And we can say, well, when we look in images, 415 00:25:09,530 --> 00:25:14,230 or when we look at things, we see low energy photons as red. 416 00:25:14,230 --> 00:25:16,970 And we see medium energy photons-- 417 00:25:16,970 --> 00:25:19,890 low energy meaning 2 electron volts is red. 418 00:25:19,890 --> 00:25:22,660 Maybe 2.5 electron volts is green. 419 00:25:22,660 --> 00:25:26,020 3 electron volts is blue. 420 00:25:26,020 --> 00:25:30,080 Well, let's do that same thing, and let's just kind of pretend 421 00:25:30,080 --> 00:25:36,590 that low energy x-ray photons will represent in our image 422 00:25:36,590 --> 00:25:43,100 as red, will represent medium energy x-ray photons as green, 423 00:25:43,100 --> 00:25:47,540 and will represent high energy x-ray photons as blue. 424 00:25:47,540 --> 00:25:50,240 It's not that that's the actual color, 425 00:25:50,240 --> 00:25:52,620 but if we were to make a true color x-ray image, 426 00:25:52,620 --> 00:25:56,490 it would just be blank, because we can't see x-ray colors. 427 00:25:56,490 --> 00:26:00,470 So what we have to do is we have to add on, 428 00:26:00,470 --> 00:26:04,230 and we represent these different energy ranges with color. 429 00:26:04,230 --> 00:26:08,430 Now, the reason we still call it a true color image-- 430 00:26:08,430 --> 00:26:11,240 where did my blue marker go? 431 00:26:11,240 --> 00:26:13,430 Is again, it's a true color image 432 00:26:13,430 --> 00:26:27,360 because now still color represents energy-- 433 00:26:27,360 --> 00:26:32,260 energy of the photons, but we have to tell people. 434 00:26:32,260 --> 00:26:34,240 When we make this true color image, 435 00:26:34,240 --> 00:26:37,750 well, red actually means any x-ray photon 436 00:26:37,750 --> 00:26:41,940 that's between 4,000 electron volts and 8,000 electron volts.