1 00:00:07,907 --> 00:00:10,432 It is dawn and the sun is rising 2 00:00:10,877 --> 00:00:15,405 as it has every day for the last 5 billion years. 3 00:00:15,782 --> 00:00:19,240 For millennia it has been a constant golden disk 4 00:00:19,486 --> 00:00:22,887 shining its unchanging light onto the Earth. 5 00:00:24,124 --> 00:00:28,891 But look through the glare and the true face of the sun is revealed. 6 00:00:29,129 --> 00:00:32,690 Not constant, but constantly changing. 7 00:00:33,133 --> 00:00:37,069 Turbulent, and violent. 8 00:00:37,971 --> 00:00:41,805 Its worst tantrums can wreak havoc on the Earth. 9 00:00:42,542 --> 00:00:44,976 To understand the sun is to understand 10 00:00:45,211 --> 00:00:48,476 the forces that drive the universe. 11 00:00:48,715 --> 00:00:54,676 If we can control those forces we can unlock the power of the stars. 12 00:00:57,624 --> 00:01:01,219 The power of our sun. 13 00:01:10,570 --> 00:01:11,662 The story of the sun 14 00:01:11,905 --> 00:01:15,636 starts 13 billion years ago with the Big Bang. 15 00:01:20,046 --> 00:01:22,606 In an instant the universe was born 16 00:01:22,849 --> 00:01:27,149 and since then it's been expanding at the speed of light. 17 00:01:27,854 --> 00:01:31,688 Within the universe there are a hundred billion galaxies. 18 00:01:31,925 --> 00:01:34,291 Our galaxy is but one of them. 19 00:01:34,527 --> 00:01:37,758 In it there are 100 billion stars. 20 00:01:38,064 --> 00:01:40,498 And towards the edge of one of the spiral arms 21 00:01:40,733 --> 00:01:43,327 is an almost insignificant dot. 22 00:01:43,570 --> 00:01:48,303 A medium-sized, not very bright, undistinguished star. 23 00:01:50,977 --> 00:01:53,502 Up close it is a different story. 24 00:01:54,314 --> 00:01:56,077 On the planets closest to the sun, 25 00:01:56,316 --> 00:01:59,183 Mercury and Venus, the heat is intense, 26 00:01:59,419 --> 00:02:01,979 their surfaces scorched. 27 00:02:05,592 --> 00:02:09,551 Further out through the solar system the sun's rays weaken. 28 00:02:09,796 --> 00:02:13,493 Until they are powerless against the chill of space. 29 00:02:15,502 --> 00:02:17,868 The outer planets are frozen. 30 00:02:19,405 --> 00:02:23,501 But in the middle lies the Goldilocks planet. 31 00:02:23,843 --> 00:02:26,334 Not too hot, and not too cold. 32 00:02:26,579 --> 00:02:29,309 In fact it's just right, 33 00:02:29,549 --> 00:02:33,315 and life has flourished in the warm glow. 34 00:02:40,360 --> 00:02:44,091 All life on Earth owes its existence to the sun. 35 00:02:44,330 --> 00:02:46,798 It powers every natural system. 36 00:02:47,066 --> 00:02:49,762 And sustains every plant and animal. 37 00:02:53,606 --> 00:02:56,302 Without the sun the planet would be a barren, 38 00:02:56,543 --> 00:02:58,704 lifeless ball of rock. 39 00:03:00,914 --> 00:03:05,647 Recognising that power humans have always worshipped the sun. 40 00:03:07,654 --> 00:03:11,215 But we have also always striven to understand it. 41 00:03:16,629 --> 00:03:19,427 These monuments are more than just temples. 42 00:03:19,666 --> 00:03:22,226 They are calendars and observatories. 43 00:03:22,468 --> 00:03:24,902 Tools for studying the sun. 44 00:03:27,173 --> 00:03:30,609 And some of them are still operational. 45 00:03:36,783 --> 00:03:42,119 This is Orkney to live here is to know the importance of the sun. 46 00:03:42,922 --> 00:03:46,255 In the summer the days are long and full of light. 47 00:03:49,829 --> 00:03:53,765 In December it's a different story. 48 00:03:54,067 --> 00:03:55,295 It's midwinter. 49 00:03:55,535 --> 00:03:59,631 It's about 11 in the morning and it's still not light completely. 50 00:03:59,906 --> 00:04:03,034 There's a strong wind coming in off the Atlantic. 51 00:04:03,276 --> 00:04:05,403 And it's cold and it's wet and 52 00:04:05,645 --> 00:04:09,479 that's pretty much typical of this time of the year up here. 53 00:04:15,655 --> 00:04:18,317 Yet despite the cold, in the stone age, 54 00:04:18,558 --> 00:04:22,426 5000 years ago a civilisation thrived here. 55 00:04:22,795 --> 00:04:26,196 The island is covered in the remains of their society. 56 00:04:30,536 --> 00:04:32,731 The ruins are full of mystery. 57 00:04:33,039 --> 00:04:35,735 We know little about the people who lived here. 58 00:04:36,142 --> 00:04:38,303 But they did leave evidence of the important role 59 00:04:38,544 --> 00:04:41,342 the sun played in their lives. 60 00:04:42,448 --> 00:04:45,906 MaesHowe - a thousand years older than the pyramids 61 00:04:46,152 --> 00:04:49,883 is one of finest examples of stone age architecture. 62 00:04:51,858 --> 00:04:56,295 On entering MaesHowe you have to crouch right down 63 00:04:56,529 --> 00:04:58,690 and you're confronted with a passage 64 00:04:59,299 --> 00:05:02,132 which seems to actually go on and on and on, 65 00:05:02,368 --> 00:05:07,567 slightly, feel an impression of going uphill, up a slope. 66 00:05:07,807 --> 00:05:10,742 And coming through clearly another doorway. 67 00:05:12,011 --> 00:05:17,745 Suddenly the whole thing opens out into the most amazing chamber. 68 00:05:18,451 --> 00:05:23,354 This alone is probably the highest and largest enclosed space 69 00:05:23,589 --> 00:05:26,752 the Neolithic Orkadians would have experienced. 70 00:05:27,360 --> 00:05:28,384 When it was excavated, 71 00:05:28,628 --> 00:05:32,530 when it was first entered back in the 19th century the clay floor 72 00:05:32,765 --> 00:05:36,462 was littered with broken pieces of human skull. 73 00:05:37,036 --> 00:05:39,197 This is a place of the dead. 74 00:05:39,739 --> 00:05:42,003 This is a house of the dead. 75 00:05:45,244 --> 00:05:46,836 Most of the time the occupants of 76 00:05:47,080 --> 00:05:50,015 the tomb were left in complete darkness. 77 00:05:53,619 --> 00:05:56,144 Then at sunset on the Winter Solstice 78 00:05:56,389 --> 00:06:00,587 the shortest day of the year something amazing happens. 79 00:06:07,200 --> 00:06:09,600 The light of the setting sun shines straight up 80 00:06:09,836 --> 00:06:13,499 the entrance tunnel and illuminates the interior. 81 00:06:15,007 --> 00:06:17,475 Well the significance is that it's marking 82 00:06:17,710 --> 00:06:20,042 the shortest time of the year, 83 00:06:20,279 --> 00:06:22,975 with the least light, and from that point on, 84 00:06:23,182 --> 00:06:25,776 slowly and gradually, the light is going to increase, 85 00:06:26,018 --> 00:06:28,043 the days are going to grow longer. 86 00:06:28,421 --> 00:06:32,016 So what's happening here, is that the dead, 87 00:06:32,258 --> 00:06:37,025 the ancestors, are being awoken on that shortest day. 88 00:06:40,666 --> 00:06:43,658 The winter solstice events at Maeshowe demonstrate 89 00:06:43,903 --> 00:06:45,894 an intimate and precise knowledge of 90 00:06:46,139 --> 00:06:48,903 the sun's movements through the sky. 91 00:06:52,044 --> 00:06:54,410 It was the first step on ourjourney to understand 92 00:06:54,647 --> 00:06:57,673 the sun and its many effects on us. 93 00:06:59,752 --> 00:07:01,947 To complete thatjourney we've had to travel to 94 00:07:02,121 --> 00:07:06,854 the furthest depths of space and to the heart of the smallest atom. 95 00:07:09,195 --> 00:07:13,495 And with every closer look the sun has always surprised us. 96 00:07:15,535 --> 00:07:20,131 To our ancestors, its power was its reliability. 97 00:07:20,373 --> 00:07:24,139 Always on time. Never changing. 98 00:07:26,579 --> 00:07:30,413 But the reality is proving to be very different. 99 00:07:30,917 --> 00:07:32,782 Most people think of the sun as quite a boring, 100 00:07:33,019 --> 00:07:34,816 constant sort of thing, but in fact it's not at all, 101 00:07:35,054 --> 00:07:36,521 it's changing all the time, 102 00:07:36,756 --> 00:07:38,986 and if you look you can see those changes on a matter 103 00:07:39,225 --> 00:07:40,283 of minutes or hours. 104 00:07:40,526 --> 00:07:42,858 And it's far from er static and boring, 105 00:07:43,095 --> 00:07:45,825 it, it's changing and it's got a life of its own. 106 00:07:47,600 --> 00:07:51,559 Modern solar observatories magnify and filter the sun's light, 107 00:07:51,804 --> 00:07:53,669 to get past the constant glare, 108 00:07:53,906 --> 00:07:56,602 and give a clear view of the surface. 109 00:08:07,086 --> 00:08:10,249 This is the actual face of the sun. 110 00:08:11,624 --> 00:08:14,115 It is turbulent and boiling. 111 00:08:14,494 --> 00:08:17,952 Never the same from one second to the next the surface bubbles 112 00:08:18,164 --> 00:08:20,564 like a giant bowl of porridge. 113 00:08:27,540 --> 00:08:31,408 Each bubble is a 1000 miles across. 114 00:08:34,280 --> 00:08:36,475 The heat and light brought to the surface 115 00:08:36,716 --> 00:08:40,584 raises its temperature to 6000 degrees centigrade. 116 00:08:40,820 --> 00:08:44,119 Enough to vaporise solid rock. 117 00:08:46,526 --> 00:08:48,494 And the sun is huge. 118 00:08:48,728 --> 00:08:52,630 You could fit the Earth inside it a million times over. 119 00:08:54,867 --> 00:08:59,463 Periodically huge explosions rip through the surface, 120 00:08:59,705 --> 00:09:04,733 releasing the energy of a billion atomic bombs in seconds. 121 00:09:05,411 --> 00:09:07,936 All this is on the surface. 122 00:09:08,147 --> 00:09:12,675 To understand the sun we must know what is going on deep inside. 123 00:09:13,486 --> 00:09:16,546 That is where the power is generated. 124 00:09:27,199 --> 00:09:30,327 So for centuries scientists have been devising ways 125 00:09:30,570 --> 00:09:32,834 to probe the heart of the sun. 126 00:09:33,105 --> 00:09:37,838 Some of them have been complex and some of them are very simple. 127 00:09:41,113 --> 00:09:46,380 And the first step is to figure outjust how powerful the sun is. 128 00:09:48,120 --> 00:09:49,883 It's easy to appreciate the power of the sun 129 00:09:50,122 --> 00:09:53,387 on a nice hot summer's day like here on the Texas Gulf Coast. 130 00:09:53,626 --> 00:09:54,388 And you can feel the power of 131 00:09:54,627 --> 00:09:56,993 the sun on your skin, sunscreens is on. 132 00:09:57,263 --> 00:09:59,231 But man the sun is just you know 133 00:09:59,465 --> 00:10:02,127 the actual physics of what's going on inside the sun, 134 00:10:02,368 --> 00:10:03,027 the power of the sun, 135 00:10:03,269 --> 00:10:04,759 the energy that the sun is releasing 136 00:10:05,004 --> 00:10:06,995 is almost beyond comprehension. 137 00:10:10,176 --> 00:10:13,111 But it is only almost beyond comprehension. 138 00:10:15,314 --> 00:10:19,648 And you can measure its power output with some simple apparatus. 139 00:10:20,519 --> 00:10:22,510 One of the earliest experiments to try and measure 140 00:10:22,755 --> 00:10:25,747 the actual power of the sun was by astronomer William Herschel 141 00:10:25,992 --> 00:10:27,254 in the 19th century, 142 00:10:27,693 --> 00:10:30,423 where he had the brilliant idea ofjust watching a piece of ice 143 00:10:30,663 --> 00:10:32,392 melt to see how long it would take and therefore 144 00:10:32,632 --> 00:10:34,930 from the properties of the ice work out 145 00:10:35,167 --> 00:10:38,625 how much sunlight was coming to the ground. 146 00:10:46,579 --> 00:10:48,843 As a demonstration of the sun's power 147 00:10:49,081 --> 00:10:50,981 it doesn't look that impressive. 148 00:10:51,450 --> 00:10:53,918 But Hershel realized that he could use the time 149 00:10:54,153 --> 00:10:56,087 it takes to melt one bit of ice to 150 00:10:56,322 --> 00:10:59,849 calculate the sun's total power output. 151 00:11:01,360 --> 00:11:04,261 So here we see the ice is almost completely melted 152 00:11:04,497 --> 00:11:06,590 in roughly 29 minutes almost half an hour. 153 00:11:06,832 --> 00:11:08,459 But Herschel was able to use this experiment 154 00:11:08,701 --> 00:11:10,066 and the time that it took to, 155 00:11:10,302 --> 00:11:14,261 to melt the ice to work out some basic properties of the sun. 156 00:11:15,408 --> 00:11:18,036 Here's how Herschel's thinking worked. 157 00:11:18,277 --> 00:11:21,041 In the time it takes to melt a slab of ice on Earth 158 00:11:21,280 --> 00:11:23,805 the sun is radiating heat in all directions 159 00:11:24,050 --> 00:11:26,610 enough to melt a complete shell of ice around it 160 00:11:26,852 --> 00:11:30,049 a diameter of 300 million kilometres. 161 00:11:30,623 --> 00:11:32,591 A shell half a centimetre thick 162 00:11:32,825 --> 00:11:36,556 and 300 million kilometres across contains a lot of ice. 163 00:11:36,796 --> 00:11:39,731 Enough to make an ice cube bigger than the Earth. 164 00:11:40,066 --> 00:11:42,796 To melt that much ice in just 30 minutes 165 00:11:43,069 --> 00:11:48,200 would take an energy input of a billion billion billion watts. 166 00:11:50,076 --> 00:11:53,307 It's a rough, but surprisingly accurate experiment 167 00:11:53,546 --> 00:11:57,915 modern satellite readings confirm the figures to within a few percent. 168 00:12:00,686 --> 00:12:04,053 It's an almost unimaginable amount of energy. 169 00:12:04,290 --> 00:12:06,281 If we could harness the sun's power output 170 00:12:06,525 --> 00:12:09,688 for a single second it would satisfy the world's energy 171 00:12:09,929 --> 00:12:13,421 demands for the next million years. 172 00:12:17,103 --> 00:12:20,698 But it's one thing to know how much power the sun is producing. 173 00:12:20,940 --> 00:12:23,500 It's something else to know how it is doing it. 174 00:12:25,211 --> 00:12:28,408 Until the middle of the 20th century no-one had any idea 175 00:12:28,647 --> 00:12:30,342 what made the sun work. 176 00:12:30,583 --> 00:12:34,280 For scientists in Hershel's time it was a mystery. 177 00:12:36,889 --> 00:12:38,686 Well one of the issues was of course what powered the sun. 178 00:12:38,924 --> 00:12:41,017 And - um - some very clever people actually 179 00:12:41,260 --> 00:12:45,026 considered the fact that the sun might be powered by burning coal. 180 00:12:46,132 --> 00:12:47,793 I mean it seems ludicrous but why not coal. 181 00:12:48,067 --> 00:12:51,059 That was an important source of energy on the earth. 182 00:12:51,303 --> 00:12:54,795 Er in that part of the 19th century 183 00:12:59,712 --> 00:13:02,180 If the sun was made entirely of coal, 184 00:13:02,414 --> 00:13:05,440 there would be one unfortunate consequence. 185 00:13:06,886 --> 00:13:11,118 It would burn itself out in just a few thousand years. 186 00:13:13,826 --> 00:13:15,885 Today that sounds ridiculous. 187 00:13:16,128 --> 00:13:20,531 But two hundred years ago it didn't seem so unlikely. 188 00:13:22,768 --> 00:13:23,826 It was widely believed that 189 00:13:24,069 --> 00:13:27,402 the Earth was only a few thousand years old. 190 00:13:32,745 --> 00:13:35,407 But in the mid-nineteenth century a new science 191 00:13:35,648 --> 00:13:36,706 was emerging that was painting 192 00:13:36,949 --> 00:13:40,646 a very different picture of the age of the Earth. 193 00:13:43,355 --> 00:13:46,381 By looking at the deepest layers of rocks geologists 194 00:13:46,625 --> 00:13:49,526 were discovering that the Earth was much older 195 00:13:49,762 --> 00:13:52,458 than anyone had previously imagined. 196 00:13:53,666 --> 00:13:56,226 If that was true then the sun also had to 197 00:13:56,468 --> 00:13:59,767 have been burning for much, much longer. 198 00:14:00,639 --> 00:14:03,472 You can see the strata and the lines in the rock in back of you 199 00:14:03,709 --> 00:14:04,971 that represent hundreds of 200 00:14:05,144 --> 00:14:07,612 millions of years of geological history. 201 00:14:08,280 --> 00:14:10,305 The top of Sacramento Peak up beyond this, 202 00:14:10,549 --> 00:14:13,109 we find fossils that are 300 million years old. 203 00:14:13,352 --> 00:14:15,980 Below Sacramento Peak you've got more than a kilometre 204 00:14:16,155 --> 00:14:18,623 of these strata that are far older than that. 205 00:14:19,925 --> 00:14:21,984 From the age of these strata geologists knew 206 00:14:22,161 --> 00:14:25,062 that the earth was at least a billion years old. 207 00:14:25,564 --> 00:14:27,361 At the same time astronomers thought 208 00:14:27,600 --> 00:14:30,160 the sun was only 10, 000 years old. 209 00:14:30,636 --> 00:14:32,866 If the geologists were right then astronomers 210 00:14:33,105 --> 00:14:37,508 had to find some other source for the Sun producing its energy. 211 00:14:41,213 --> 00:14:42,771 The search for the source of energy 212 00:14:43,048 --> 00:14:45,573 that could power the sun for billions of years 213 00:14:45,818 --> 00:14:48,480 lasted for nearly a century. 214 00:14:50,723 --> 00:14:53,749 Eventually scientists would find the answer in the forces 215 00:14:54,059 --> 00:14:58,894 that hold atoms together and in the nature of matter itself. 216 00:14:59,999 --> 00:15:03,958 But first you have to know what the sun is made of. 217 00:15:05,437 --> 00:15:10,534 To find that out you need to take a very close look at sunlight. 218 00:15:19,818 --> 00:15:22,651 When you take the light from the Sun and pass it through a prism, 219 00:15:22,888 --> 00:15:24,150 spread it out into the colours, 220 00:15:24,390 --> 00:15:26,756 as you look through it you notice that it isn't uniform, 221 00:15:27,026 --> 00:15:28,789 that there are places that are darker. 222 00:15:29,028 --> 00:15:32,088 Each of those dark lines is due to a specific chemical element. 223 00:15:32,331 --> 00:15:36,563 Each element has its own series of lines that are specific to it. 224 00:15:39,038 --> 00:15:43,065 Each chemical element absorbs light at specific frequencies 225 00:15:43,309 --> 00:15:45,573 removing a strip from the spectrum. 226 00:15:46,378 --> 00:15:48,812 As the light passes through the sun, 227 00:15:49,048 --> 00:15:51,414 all the elements leave their mark. 228 00:15:51,650 --> 00:15:54,346 So when the light arrives at the Earth it contains 229 00:15:54,586 --> 00:15:57,646 the complete chemical formula of the sun. 230 00:16:01,694 --> 00:16:04,788 If we take the spectrum and spread it out to fine details 231 00:16:05,030 --> 00:16:06,588 and what we've done here is stacked up 232 00:16:06,832 --> 00:16:08,823 pieces of the spectrum one on top of each other 233 00:16:09,068 --> 00:16:11,127 you see all of these dark areas. 234 00:16:11,370 --> 00:16:13,531 The key to figuring out how much of these elements 235 00:16:13,772 --> 00:16:16,832 are there is the breadth and the depth of the line; 236 00:16:17,076 --> 00:16:19,442 how dark is the line and how broad is it. 237 00:16:23,415 --> 00:16:27,442 The composition of the sun lies in this bar code. 238 00:16:28,921 --> 00:16:33,017 All the thin lines are caused by tiny amounts of complex elements 239 00:16:33,258 --> 00:16:36,056 metals like iron and magnesium. 240 00:16:36,729 --> 00:16:39,425 But there are 3 very deep, broad lines, 241 00:16:39,665 --> 00:16:40,689 and they are all caused by 242 00:16:40,933 --> 00:16:43,902 an enormous amount of a single element. 243 00:16:47,039 --> 00:16:50,065 There's some helium and traces of heavier elements. 244 00:16:50,309 --> 00:16:54,245 But over 90% of the sun is Hydrogen. 245 00:17:00,119 --> 00:17:03,782 It is the simplest and most common element in the universe. 246 00:17:05,791 --> 00:17:09,955 The secrets of the sun's power must lie in this gas. 247 00:17:13,399 --> 00:17:15,799 Look carefully into the night sky 248 00:17:16,035 --> 00:17:17,332 and you'll see huge clouds of 249 00:17:17,569 --> 00:17:21,005 hydrogen floating in interstellar space. 250 00:17:24,009 --> 00:17:26,034 These are nebulae. 251 00:17:26,278 --> 00:17:29,714 And they can be hundreds of light years across. 252 00:17:35,287 --> 00:17:38,188 They are some of the brightest areas in the sky 253 00:17:38,424 --> 00:17:43,020 lit up by the intense light of newly formed massive stars. 254 00:17:43,262 --> 00:17:47,062 In them we can see stars being born. 255 00:17:50,469 --> 00:17:52,733 It is to areas like this that astronomers turn 256 00:17:53,038 --> 00:17:57,532 their telescopes when they want to study how our sun was formed. 257 00:17:58,744 --> 00:18:03,340 There she is, okay, so now let's recentre on her. 258 00:18:09,521 --> 00:18:12,149 By studying different nebulae it's possible to 259 00:18:12,391 --> 00:18:15,827 piece together the stages in which stars are made. 260 00:18:21,567 --> 00:18:24,331 And it all starts in a cold dark cloud, 261 00:18:24,570 --> 00:18:27,835 floating around waiting for something to happen. 262 00:18:29,508 --> 00:18:32,500 Cold clouds like this are actually quite stable. 263 00:18:32,744 --> 00:18:34,803 They will sit there for a very very long time, 264 00:18:35,047 --> 00:18:36,844 for thousands and in some cases millions of years 265 00:18:37,082 --> 00:18:38,743 before they'll actually do anything. 266 00:18:39,017 --> 00:18:41,508 What you need to do to get the star formation process going 267 00:18:41,753 --> 00:18:43,983 is you need to kick it with something. 268 00:18:45,657 --> 00:18:48,182 That can be the impact on the cloud 269 00:18:48,427 --> 00:18:50,793 from one side by a supernova blast wave; 270 00:18:51,029 --> 00:18:54,760 a massive star nearby has gone boom at the end of its life 271 00:18:55,033 --> 00:18:58,366 and that sends out in all directions very energetic 272 00:18:58,604 --> 00:19:03,632 compression waves that hit the gas and compress it. 273 00:19:05,144 --> 00:19:08,113 The shock waves knock the cloud out of balance. 274 00:19:08,347 --> 00:19:11,407 Causing localised clumps of hydrogen to form. 275 00:19:13,886 --> 00:19:17,049 These are the seeds from which stars grow. 276 00:19:19,124 --> 00:19:22,184 The increased gravity of the seeds sucks in more 277 00:19:22,427 --> 00:19:24,952 and more hydrogen in a runaway process 278 00:19:25,164 --> 00:19:27,962 that lasts for a million years. 279 00:19:30,169 --> 00:19:35,072 As more hydrogen is squeezed into the clumps the temperature rises. 280 00:19:36,708 --> 00:19:38,801 They are not yet producing light 281 00:19:39,044 --> 00:19:42,480 but they are well on the way to becoming stars. 282 00:19:43,382 --> 00:19:45,179 As they grow bigger and bigger, 283 00:19:45,417 --> 00:19:47,885 they start to spin and throw out a disk of debris 284 00:19:48,120 --> 00:19:51,487 that will coalesce to form a solar system. 285 00:19:54,026 --> 00:19:56,256 This kind of process is exactly the kind of process 286 00:19:56,495 --> 00:19:58,463 that would have formed our solar system. 287 00:19:58,697 --> 00:20:00,164 When we look at our solar system, 288 00:20:00,399 --> 00:20:04,733 all of the planets rotate around the sun in the same direction 289 00:20:04,970 --> 00:20:10,272 and they all are in the same plane the same flat sheet around our sun, 290 00:20:10,509 --> 00:20:12,773 and this is exactly a consequence of the fact 291 00:20:13,011 --> 00:20:18,244 that the early solar system formed out of a broad disc. 292 00:20:19,985 --> 00:20:22,010 With the solar-system in place all 293 00:20:22,254 --> 00:20:25,712 that is left is for the young star to light up. 294 00:20:25,958 --> 00:20:29,792 When it happens it is sudden and irreversible. 295 00:20:31,697 --> 00:20:35,064 Ultimately the process starts 296 00:20:37,736 --> 00:20:42,969 and because it liberates so much energy with that first fusion, 297 00:20:43,208 --> 00:20:45,199 then the process takes off. 298 00:20:45,444 --> 00:20:49,540 Um - it lights up a large area and it starts to shine on its own 299 00:20:49,781 --> 00:20:50,713 within a matter of minutes. 300 00:20:50,949 --> 00:20:52,814 It's a very quick process. 301 00:20:56,255 --> 00:20:58,621 In that first burst of light the star 302 00:20:58,857 --> 00:21:01,553 has begun its lifelong activity as a factory 303 00:21:01,793 --> 00:21:04,261 for making other chemical elements. 304 00:21:06,765 --> 00:21:11,725 Every atom in everything around us was made in the heart of a star 305 00:21:12,204 --> 00:21:15,833 and all were made from the same starting ingredient. 306 00:21:20,312 --> 00:21:23,076 The simplest element that we have is hydrogen 307 00:21:23,348 --> 00:21:25,839 and it's actually the building block 308 00:21:26,084 --> 00:21:28,314 for all the other elements that we have. 309 00:21:31,056 --> 00:21:34,389 In the heart of the sun hydrogen nuclei 310 00:21:34,626 --> 00:21:39,757 protons - are stuck together to make heliumlt sounds straightforward 311 00:21:40,065 --> 00:21:43,432 but it can only happen in the most extreme conditions. 312 00:21:43,835 --> 00:21:45,632 In order for these protons to come together, 313 00:21:45,871 --> 00:21:47,338 because they're both positively charged 314 00:21:47,572 --> 00:21:48,732 they don't want to come together, 315 00:21:48,974 --> 00:21:51,272 they've actually got to be pushed together. 316 00:21:53,445 --> 00:21:55,470 In order to do this you need very high temperatures 317 00:21:55,714 --> 00:21:58,046 so they're moving very fast and you also need very, 318 00:21:58,250 --> 00:21:59,979 very high pressures. 319 00:22:01,920 --> 00:22:05,720 The only part of the sun that is hot and dense enough is the core. 320 00:22:06,024 --> 00:22:08,788 An area that contains over half the star's mass 321 00:22:09,027 --> 00:22:11,689 in less than 2 percent of its volume. 322 00:22:14,666 --> 00:22:17,567 Here at 15 million degrees the protons 323 00:22:17,803 --> 00:22:21,000 are bashed together so hard that they fuse. 324 00:22:23,375 --> 00:22:25,605 A helium nucleus is a tiny bit lighter 325 00:22:25,844 --> 00:22:30,144 than the combined mass of the 4 protons it is made from. 326 00:22:33,719 --> 00:22:35,653 And as Einstein tells us it is 327 00:22:35,887 --> 00:22:40,017 that tiny bit of lost mass that provides the power. 328 00:22:41,326 --> 00:22:44,591 Energy is equal to mass times the speed of light, 329 00:22:44,830 --> 00:22:46,730 times the speed of light. 330 00:22:47,065 --> 00:22:50,193 Now the speed of light is a very, very big number. 331 00:22:50,435 --> 00:22:52,699 So if we just take a small amount of mass, 332 00:22:52,938 --> 00:22:54,405 you get a huge amount of energy. 333 00:22:54,639 --> 00:22:57,574 And that's the energy which actually powers our sun. 334 00:23:00,078 --> 00:23:05,380 Every second 5 million tonnes of the sun is converted to pure energy. 335 00:23:05,617 --> 00:23:08,484 And although it has been burning for 5 billion years 336 00:23:08,720 --> 00:23:11,985 it is only half way through its supplies of hydrogen. 337 00:23:13,091 --> 00:23:14,820 The light produced in the core must travel 338 00:23:15,060 --> 00:23:18,086 over half a million kilometres to the surface. 339 00:23:18,330 --> 00:23:20,594 And it does so very slowly. 340 00:23:20,899 --> 00:23:23,868 The heart of the sun is so dense that the speed of light is less 341 00:23:24,102 --> 00:23:26,900 than 1 mm a second. 342 00:23:28,540 --> 00:23:30,770 It can take two hundred thousand years 343 00:23:31,042 --> 00:23:34,739 for the light to travel from the core to the surface. 344 00:23:35,180 --> 00:23:39,844 It takes just another 8 minutes to get to the Earth. 345 00:23:45,690 --> 00:23:48,250 This is what the power of nuclear fusion looks like 346 00:23:48,493 --> 00:23:51,621 from 150 million kilometres away. 347 00:23:55,600 --> 00:23:58,194 This is what it looks like close up. 348 00:24:01,106 --> 00:24:03,131 The H bomb was man's first attempt 349 00:24:03,375 --> 00:24:05,843 at recreating the sun on Earth. 350 00:24:06,077 --> 00:24:07,977 A balloon full of hydrogen squeezed 351 00:24:08,146 --> 00:24:10,671 until it released its energy. 352 00:24:18,156 --> 00:24:21,990 In contrast to its destructive power it's long been realised 353 00:24:22,227 --> 00:24:24,092 that controlled nuclear fusion 354 00:24:24,329 --> 00:24:27,457 could solve the world's energy problems. 355 00:24:30,235 --> 00:24:34,365 It has been one of the holy grails of science for half a century. 356 00:24:37,209 --> 00:24:39,905 This kind of power, the H-bomb, 357 00:24:40,145 --> 00:24:42,739 is a man-made version of this, the sun. 358 00:24:43,048 --> 00:24:45,243 In 1958 Britain announced that 359 00:24:45,484 --> 00:24:47,475 she could produce this power in the laboratory, 360 00:24:47,719 --> 00:24:49,209 in a machine called Zeta. 361 00:24:49,454 --> 00:24:51,319 There is a real prospect of unlimited energy 362 00:24:51,556 --> 00:24:54,024 from controlled thermo-nuclear fusion. 363 00:24:55,460 --> 00:24:58,759 Unfortunately it wasn't that easy. 364 00:25:00,866 --> 00:25:03,528 But now, nearly fifty years later, 365 00:25:03,768 --> 00:25:06,737 in the same laboratories in Oxfordshire scientists 366 00:25:07,005 --> 00:25:11,374 are finally managing to create their own star on Earth. 367 00:25:19,851 --> 00:25:21,216 ...ready when you are. 368 00:25:21,453 --> 00:25:22,977 Okay, ready. 369 00:25:26,124 --> 00:25:29,890 ...shot, one four six five eight... 370 00:25:35,534 --> 00:25:38,526 shot eighty five seconds. 371 00:25:46,578 --> 00:25:48,808 It might not seem like much 372 00:25:51,616 --> 00:25:56,713 but slowed down by 300 times the pictures reveal how the gas plasma 373 00:25:56,955 --> 00:25:59,480 is being squeezed and heated to create 374 00:25:59,724 --> 00:26:03,683 the most extreme conditions in the solar system. 375 00:26:05,997 --> 00:26:09,865 Plasmas I always like to think of as being like naughty children. 376 00:26:10,101 --> 00:26:12,296 They're full of energy and they are, 377 00:26:12,537 --> 00:26:15,973 want to misbehave and it's ourjob to try 378 00:26:16,141 --> 00:26:18,507 and control that misbehaviour. 379 00:26:20,879 --> 00:26:23,313 For the particles to fuse on Earth 380 00:26:23,548 --> 00:26:25,539 the temperatures need to be raised to 10 times 381 00:26:25,784 --> 00:26:28,446 those found at the heart of the sun. 382 00:26:30,255 --> 00:26:33,224 Bombarding the gas with a stream of fast neutrons 383 00:26:33,458 --> 00:26:37,360 raises the temperature to over 100 million degrees. 384 00:26:39,531 --> 00:26:44,093 Only then can the energy of nuclear fusion be released. 385 00:26:46,371 --> 00:26:49,397 After years of learning to control the plasma, 386 00:26:49,641 --> 00:26:51,006 scientists now believe they are 387 00:26:51,176 --> 00:26:54,737 within sight of harnessing the sun's power. 388 00:26:59,317 --> 00:27:02,218 The aim of it is to be able to produce cheap, 389 00:27:02,454 --> 00:27:05,287 clean and effectively an inexhaustible supply 390 00:27:05,523 --> 00:27:08,651 of electricity for future generations. 391 00:27:10,095 --> 00:27:13,223 This is only small experimental reactor. 392 00:27:13,465 --> 00:27:15,399 It can only run for a few seconds 393 00:27:15,634 --> 00:27:18,831 and sucks up more energy than it creates. 394 00:27:20,171 --> 00:27:22,401 But the next generation of bigger reactors 395 00:27:22,641 --> 00:27:25,007 is already being built. 396 00:27:26,878 --> 00:27:29,278 When operational they will produce 10 times 397 00:27:29,514 --> 00:27:31,846 more power energy than they use. 398 00:27:32,083 --> 00:27:34,051 They will be stars on Earth. 399 00:27:34,285 --> 00:27:37,448 Power stations that won't deplete natural resources 400 00:27:37,689 --> 00:27:40,385 or produce dangerous waste products. 401 00:27:40,925 --> 00:27:42,358 It sounds great. 402 00:27:42,594 --> 00:27:45,062 But recreating the sun isn't easy 403 00:27:45,296 --> 00:27:47,355 and it may be another 50 years 404 00:27:47,599 --> 00:27:51,091 before the fusion power station becomes reality. 405 00:27:59,210 --> 00:28:01,007 Until then we'll just have to make do 406 00:28:01,246 --> 00:28:02,941 with the real thing. 407 00:28:03,114 --> 00:28:04,945 But that's not so bad. 408 00:28:05,150 --> 00:28:08,608 Just seeing sunlight is enough to cheer us up. 409 00:28:12,991 --> 00:28:15,016 Well many people think it's the warmth of the sun 410 00:28:15,260 --> 00:28:17,694 that is associated with us feeling good 411 00:28:17,996 --> 00:28:19,258 and of course that's true. 412 00:28:19,497 --> 00:28:21,727 But in fact research has shown that it's not really 413 00:28:22,000 --> 00:28:25,492 the warmth it's actually the light that's important. 414 00:28:26,771 --> 00:28:29,365 Sunlight controls our daily cycle 415 00:28:29,607 --> 00:28:33,600 making sure we wake up in the morning and go to sleep at night. 416 00:28:41,820 --> 00:28:45,256 When there's not enough light those patterns get disturbed 417 00:28:45,490 --> 00:28:47,515 with miserable effect. 418 00:28:48,760 --> 00:28:52,423 It's a clinical fact that depression is more common in winter 419 00:28:52,664 --> 00:28:54,689 because of the lack of sunlight 420 00:28:54,933 --> 00:28:59,131 they call it SAD seasonal affective disorder. 421 00:29:01,639 --> 00:29:04,437 Seasonal affective disorder is a depressive illness 422 00:29:04,676 --> 00:29:07,975 in the starts during the autumn and early winter. 423 00:29:08,213 --> 00:29:12,513 And usually goes away completely during the spring and early summer. 424 00:29:13,618 --> 00:29:16,018 Some people feel quite miserable and depressed 425 00:29:16,254 --> 00:29:19,155 and gloomy during the winter months. 426 00:29:19,390 --> 00:29:21,654 And some people, a small proportion, 427 00:29:21,893 --> 00:29:25,192 will go on to develop clinically significant depression 428 00:29:25,430 --> 00:29:27,159 which requires treatment. 429 00:29:38,343 --> 00:29:40,038 This is Rattenburg, 430 00:29:40,278 --> 00:29:44,442 a fairy tale Austrian village cursed by lack of sunlight. 431 00:29:47,085 --> 00:29:50,646 Due to a quirk of geology it gets no sunlight at all 432 00:29:50,889 --> 00:29:53,187 between November and February. 433 00:29:54,058 --> 00:29:57,516 During those winter months the sun never rises high enough 434 00:29:57,762 --> 00:30:00,526 to clear the brow of Rat mountain. 435 00:30:02,200 --> 00:30:05,192 And the town lies in permanent shadow, 436 00:30:06,104 --> 00:30:10,473 while it's neighbour across the river basks in the sunshine. 437 00:30:10,842 --> 00:30:12,707 In winter of course it's very cold, 438 00:30:12,944 --> 00:30:17,005 it's shadow and as you can imagine it's cold, 439 00:30:17,248 --> 00:30:19,773 we are freezing and if you want to have some sun 440 00:30:20,018 --> 00:30:22,714 you have to move to the next village. 441 00:30:22,987 --> 00:30:25,114 It makes you happier to sit in the sunlight 442 00:30:25,356 --> 00:30:27,881 and not to freeze in the shadow. 443 00:30:31,062 --> 00:30:34,054 Frozen and in the dark the residents have been 444 00:30:34,299 --> 00:30:35,789 forced to take desperate measures to bring 445 00:30:36,034 --> 00:30:38,502 some light into their lives. 446 00:30:42,674 --> 00:30:45,973 Helmar Zangirl is a lighting expert who specialises 447 00:30:46,211 --> 00:30:48,236 in bringing natural light in to some of 448 00:30:48,479 --> 00:30:50,879 the world's biggest buildings. 449 00:30:51,549 --> 00:30:55,041 He may be the salvation of Rattenburg. 450 00:30:57,555 --> 00:30:59,216 Evolutionary speaking, 451 00:30:59,457 --> 00:31:03,689 man has adapted to natural light and has adapted to the sun, 452 00:31:03,928 --> 00:31:06,897 and if you deprive man of the sun er, 453 00:31:07,131 --> 00:31:12,000 clearly its, it's a different quality of life. 454 00:31:12,804 --> 00:31:15,170 How do you feel if you sit for one week in a, 455 00:31:15,406 --> 00:31:17,806 a place with fog? 456 00:31:18,610 --> 00:31:21,272 And how do you feel when you sit for one day 457 00:31:21,512 --> 00:31:23,537 in a place where the sun shines? 458 00:31:23,781 --> 00:31:26,011 I personally feel so much happier in the sunshine, 459 00:31:26,184 --> 00:31:27,583 I can tell you that. 460 00:31:31,256 --> 00:31:33,781 The solution for Rattenburg is simple. 461 00:31:34,058 --> 00:31:37,755 Steal some of the sunlight from the other side of the valley. 462 00:31:39,297 --> 00:31:42,630 Eventually a huge system of mirrors will reflect the light of 463 00:31:42,867 --> 00:31:47,133 the sun to a second set of mirrors on the castle above the town 464 00:31:47,972 --> 00:31:50,463 and then reflect it down into the streets 465 00:31:50,708 --> 00:31:54,041 to brighten the lives of the citizens of Rattenburg. 466 00:31:54,579 --> 00:31:56,479 Well the main effect for the people in town will be 467 00:31:56,714 --> 00:32:00,309 that er part of the facades of the buildings 468 00:32:00,551 --> 00:32:03,042 and parts of the street at least, of the main street, 469 00:32:03,288 --> 00:32:05,654 will be brightly illuminated and 470 00:32:05,890 --> 00:32:08,984 will clearly be recognised as sunlight. 471 00:32:14,098 --> 00:32:16,532 It sounds crazy but it's true. 472 00:32:16,768 --> 00:32:20,363 People will go to the extraordinary lengths for a bit of sunlight. 473 00:32:25,343 --> 00:32:28,676 But the sun is much more than a giant lightbulb. 474 00:32:31,516 --> 00:32:34,144 There are other forces at work in the sun. 475 00:32:38,156 --> 00:32:41,887 Forces that change over minutes and over years. 476 00:32:43,394 --> 00:32:46,591 Forces that tear the surface apart. 477 00:32:47,899 --> 00:32:50,424 We are only now beginning to understand these forces 478 00:32:50,668 --> 00:32:53,228 and the effects they have on the Earth. 479 00:32:53,638 --> 00:32:57,039 But we have known about them for hundreds of years. 480 00:32:57,241 --> 00:33:00,768 Because the sun gets spots. 481 00:33:03,481 --> 00:33:06,473 Sun spots are dark regions on the surface of the Sun, 482 00:33:06,718 --> 00:33:09,983 typically about the size of the Earth in terms of area. 483 00:33:10,154 --> 00:33:12,247 Here's a live shot of one today. 484 00:33:12,490 --> 00:33:15,288 Unfortunately we've got a very windy day with high thin clouds, 485 00:33:15,526 --> 00:33:18,154 so the picture's bouncing around and not very sharp, 486 00:33:18,396 --> 00:33:19,863 but with very high resolution images we can show 487 00:33:20,098 --> 00:33:22,623 detailed structure in the sun spot. 488 00:33:42,820 --> 00:33:44,253 The inner part of the sun spot, 489 00:33:44,489 --> 00:33:47,117 the dark umbra as we call it is dark 490 00:33:47,358 --> 00:33:49,656 only in comparison to the rest of the sun. 491 00:33:50,294 --> 00:33:52,023 It's actually bright enough that it would blind you 492 00:33:52,230 --> 00:33:54,528 if you looked at it alone. 493 00:33:56,067 --> 00:33:58,262 The spots are not static. 494 00:33:59,070 --> 00:34:02,335 These video images show the edges of the spot crawling, 495 00:34:02,573 --> 00:34:05,371 almost as if it was alive. 496 00:34:21,059 --> 00:34:25,462 The movements of sunspots have been studied for four hundrand years. 497 00:34:25,696 --> 00:34:28,859 Ever since Galileo trained his telescope on the sun 498 00:34:29,100 --> 00:34:32,729 and made the first crucial discovery about its behaviour. 499 00:34:34,705 --> 00:34:38,038 Surprised to see black dots creeping over the surface 500 00:34:38,276 --> 00:34:40,744 he kept track of them over a number of days 501 00:34:41,045 --> 00:34:44,378 and found that they were all moving in the same direction. 502 00:34:48,386 --> 00:34:50,911 To Galileo the meaning was clear 503 00:34:51,155 --> 00:34:53,089 the sun was rotating 504 00:34:53,324 --> 00:34:57,351 and was turning faster at the equator than at the poles. 505 00:34:58,563 --> 00:35:00,622 It was a discovery that was to prove critical 506 00:35:00,865 --> 00:35:04,062 in our understanding of how the sun works. 507 00:35:06,104 --> 00:35:08,698 Ever since Galileo records have been 508 00:35:09,006 --> 00:35:11,338 kept of the coming and goings of sunspots 509 00:35:11,576 --> 00:35:14,272 and variations soon became clear. 510 00:35:14,645 --> 00:35:17,978 Sometimes the sun is covered in hundreds of spots 511 00:35:18,216 --> 00:35:20,844 other times there are none at all. 512 00:35:21,619 --> 00:35:25,385 And after a while a pattern emerged. 513 00:35:26,491 --> 00:35:29,085 If you observe sun spots over several years, 514 00:35:29,327 --> 00:35:31,989 they come and go with an about an eleven year cycle. 515 00:35:32,163 --> 00:35:34,723 From solar minimum where there can be no spots at all 516 00:35:35,032 --> 00:35:37,432 on the sun for weeks or months at a time, 517 00:35:37,668 --> 00:35:40,193 to at maximum where you can have a hundred spots visible 518 00:35:40,438 --> 00:35:43,566 on the surface of the sun, and then they decline again, 519 00:35:43,808 --> 00:35:47,039 usually over about six years or so, to, back to minimum. 520 00:35:49,947 --> 00:35:54,008 Until recently no-one knew what was driving the solar cycle. 521 00:35:54,185 --> 00:35:56,585 Or where sun spots came from. 522 00:36:00,358 --> 00:36:04,021 But people had always suspected that the scars on the suns surface 523 00:36:04,262 --> 00:36:06,287 had an effect on the Earth. 524 00:36:06,531 --> 00:36:09,762 But no-one could quite put their finger on what it was. 525 00:36:11,903 --> 00:36:14,167 It has been correlated with all kinds of different things, 526 00:36:14,405 --> 00:36:17,966 er the price of wheat, the thickness of fur on animals, 527 00:36:18,142 --> 00:36:19,439 I'm inundated with it every day. 528 00:36:19,677 --> 00:36:22,407 I got a guy that comes to my website to try and predict the, 529 00:36:22,647 --> 00:36:26,014 the stock market from the daily sunspot areas. 530 00:36:26,250 --> 00:36:28,741 You know, 'oh, you didn't post them today, I gotta know! ' 531 00:36:29,020 --> 00:36:32,456 So, are you making money or what, I want some if you are. 532 00:36:37,461 --> 00:36:42,398 One effect sun spots do have on the earth is on the climate. 533 00:36:44,035 --> 00:36:46,162 But it is a subtle effect. 534 00:36:46,404 --> 00:36:47,393 Its greatest impact was 535 00:36:47,638 --> 00:36:51,267 only noticed 3 hundred years after the event. 536 00:36:56,247 --> 00:37:00,616 It was discovered in Greenwich by the astronomer Robert Maunder 537 00:37:00,851 --> 00:37:03,547 who was studying the hundreds of years of sunspot records 538 00:37:03,788 --> 00:37:06,723 held at the Royal Observatory. 539 00:37:10,461 --> 00:37:12,986 And in the late part of the 19th century he er 540 00:37:13,231 --> 00:37:15,096 became particularly interested in the sunspots. 541 00:37:15,333 --> 00:37:17,801 He discovered that there had been this peculiar effect 542 00:37:18,035 --> 00:37:20,560 in the second half of the 17th and the 18th centuries 543 00:37:20,805 --> 00:37:22,966 when the sunspot numbers diminished to a real, 544 00:37:23,140 --> 00:37:24,971 really a fraction of what they are today. 545 00:37:25,176 --> 00:37:27,736 And he described this as the Maunder minimum. 546 00:37:33,484 --> 00:37:40,253 For seventy years, from 1645-1715 sunspots disappeared. 547 00:37:40,491 --> 00:37:44,484 It was as if the engine that drives the solar cycle had stopped. 548 00:37:45,429 --> 00:37:48,455 And it correlated almost exactly with the last period 549 00:37:48,699 --> 00:37:52,396 of prolonged cold to strike the Northern hemisphere. 550 00:37:52,637 --> 00:37:55,731 They call it the Little Ice Age. 551 00:37:59,443 --> 00:38:01,377 What's interesting about a period like the little ice age is 552 00:38:01,612 --> 00:38:04,410 that you don't necessarily see a very large dip in temperatures, 553 00:38:04,649 --> 00:38:06,276 but nonetheless even a degree or two 554 00:38:06,517 --> 00:38:08,815 is enough to see some really quite dramatic effects, 555 00:38:09,053 --> 00:38:11,681 like pack ice advancing south from the north pole, 556 00:38:11,989 --> 00:38:14,981 like the Viking colonies in Greenland being wiped out 557 00:38:15,226 --> 00:38:17,126 by the changing climate and the population 558 00:38:17,361 --> 00:38:19,761 of Iceland falling by half. 559 00:38:21,732 --> 00:38:24,098 Now in Britain the weather was cold enough 560 00:38:24,335 --> 00:38:26,269 that the Thames would regularly freeze in winter 561 00:38:26,504 --> 00:38:29,564 and one of the classic depictions of life at the time is Frost Fairs, 562 00:38:29,807 --> 00:38:32,503 when the population would hold a fair on the frozen river. 563 00:38:32,743 --> 00:38:35,837 So things really must have been a lot harsher than they are today. 564 00:38:42,853 --> 00:38:46,482 When the sunspots disappeared something on the sun changed 565 00:38:46,724 --> 00:38:48,589 that cooled the Earth down. 566 00:38:49,226 --> 00:38:51,990 But it wasn't that the solar output changed. 567 00:38:52,229 --> 00:38:54,322 No matter how many sunspots there are 568 00:38:54,565 --> 00:38:57,557 the sun doesn't get any hotter or brighter. 569 00:39:03,841 --> 00:39:06,935 So the spots must have another effect. 570 00:39:07,111 --> 00:39:10,740 And to see it we need a different way to look at the sun. 571 00:39:17,888 --> 00:39:19,651 It's notjust heat and light that that the sun 572 00:39:19,890 --> 00:39:21,721 is throwing at the Earth. 573 00:39:22,593 --> 00:39:26,791 As every sunbather knows, there's ultraviolet light too. 574 00:39:29,533 --> 00:39:33,128 Enough UV reaches the surface to burn our skin, 575 00:39:33,371 --> 00:39:36,499 but it is only fraction of the sun's UV output. 576 00:39:38,342 --> 00:39:41,402 The rest is filtered out by the atmosphere. 577 00:39:43,347 --> 00:39:47,545 It means we don't get a complete picture of the sun from the Earth. 578 00:39:47,818 --> 00:39:52,755 To see the sun in all its glory you have to go into space. 579 00:40:09,240 --> 00:40:13,142 From here you can see the changing sun. 580 00:40:20,718 --> 00:40:25,519 In the extreme UV the sunspots burn a brilliant white. 581 00:40:34,331 --> 00:40:38,267 In the X-ray frequencies they look even more dramatic. 582 00:40:38,502 --> 00:40:42,598 Huge plumes of superheated gas spout from the spots. 583 00:40:48,412 --> 00:40:49,379 When you're seeing the visible 584 00:40:49,613 --> 00:40:51,308 you're really seeing the surface of the sun. 585 00:40:51,615 --> 00:40:52,445 But when you're seeing the ultraviolet 586 00:40:52,683 --> 00:40:55,345 or the x-rays you're actually seeing that very hot atmosphere, 587 00:40:55,586 --> 00:40:56,985 and that's about a million degrees, 588 00:40:57,221 --> 00:40:59,519 whereas the surface is about six thousand degrees. 589 00:40:59,757 --> 00:41:01,054 So you're seeing a different part of the sun 590 00:41:01,292 --> 00:41:05,558 And you're seeing a part that's constantly changing. 591 00:41:08,766 --> 00:41:11,462 These phenomenal displays of solar power 592 00:41:11,702 --> 00:41:17,004 were only discovered in the 1970s, by the astronauts on Skylab. 593 00:41:25,583 --> 00:41:29,110 No-one had seen the sun like this before. 594 00:41:34,692 --> 00:41:38,355 Since then a number of Space telescopes have been deployed 595 00:41:38,596 --> 00:41:41,531 whose sole purpose is to look at the sun. 596 00:41:44,101 --> 00:41:49,539 The most used is Soho the Solar and Heliospheric Observatory. 597 00:41:51,275 --> 00:41:54,108 It sits a million miles away from the Earth 598 00:41:54,345 --> 00:41:56,040 at the Lagrangian point 599 00:41:56,247 --> 00:42:00,149 where the gravitational pull from the Earth and the sun is equal. 600 00:42:00,384 --> 00:42:02,682 Fixed in space it has an uninterrupted 601 00:42:02,920 --> 00:42:06,048 view of the sun and its tantrums. 602 00:42:08,492 --> 00:42:10,858 It has completely transformed our understanding 603 00:42:11,095 --> 00:42:14,690 you can essentially see right from inside the sun, 604 00:42:14,932 --> 00:42:17,332 right through to the coronal mass ejections 605 00:42:17,568 --> 00:42:18,364 as they're leaving the sun, 606 00:42:18,602 --> 00:42:21,127 so you're seeing way out to 30 solar radii. 607 00:42:22,840 --> 00:42:25,400 Soho has played a key role in understanding 608 00:42:25,643 --> 00:42:28,612 the explosive power of the sun. 609 00:42:29,380 --> 00:42:32,838 By blocking out the discit simulates an eclipse, 610 00:42:33,083 --> 00:42:34,812 revealing the outer atmosphere and 611 00:42:35,052 --> 00:42:38,886 the true scale of the sun's largest eruptions. 612 00:42:41,659 --> 00:42:45,618 These are solar flares and coronal mass ejections 613 00:42:45,863 --> 00:42:49,026 and they erupt from the heart of sunspots. 614 00:42:53,804 --> 00:42:56,272 The temperatures in a solar flare will be tens of 615 00:42:56,507 --> 00:43:00,102 millions of degrees so it's an extremely hot, 616 00:43:00,344 --> 00:43:03,871 very dramatic change in temperature over a short period of time. 617 00:43:05,316 --> 00:43:08,080 When they erupt completely you can get masses 618 00:43:08,319 --> 00:43:09,718 which are roughly the mass of Mount Everest 619 00:43:10,020 --> 00:43:12,989 being flung out into the solar system. 620 00:43:14,925 --> 00:43:18,486 At solar minimum, flares are infrequent. 621 00:43:19,063 --> 00:43:23,727 But every 11 years when the cycle peaks, at solar max, 622 00:43:24,034 --> 00:43:29,233 the sun puts on the best firework display in the solar system. 623 00:43:46,156 --> 00:43:48,021 Solar astronomers are now beginning to 624 00:43:48,225 --> 00:43:51,319 understand the cause of these explosions. 625 00:43:53,364 --> 00:43:56,128 They are not caused by the power of fusion. 626 00:43:56,367 --> 00:43:58,892 There is another force at work. 627 00:43:59,136 --> 00:44:01,866 It is the force of magnetism. 628 00:44:03,040 --> 00:44:07,534 The sun is covered in a complex network magnetic fields. 629 00:44:07,778 --> 00:44:10,770 A magnetic map of the sun a familiar patchwork 630 00:44:11,015 --> 00:44:13,142 on the face of the sun. 631 00:44:14,084 --> 00:44:17,451 The areas of the strongest fields coincide exactly 632 00:44:17,688 --> 00:44:20,054 with the position of sunspots. 633 00:44:22,092 --> 00:44:27,553 Here the magnetic field strength can be amplified 10,000 times. 634 00:44:29,733 --> 00:44:32,531 It turns out that the regions of the strongest magnetic field 635 00:44:32,770 --> 00:44:35,238 on the sun are in the sunspots. 636 00:44:35,472 --> 00:44:37,804 And in the units that we use sunspot magnetic fields 637 00:44:38,042 --> 00:44:40,010 are roughly a thousand, 638 00:44:40,177 --> 00:44:42,304 two thousand, maybe three thousand gauss. 639 00:44:42,546 --> 00:44:44,912 But if you look at magnets like the ones I'm playing with here, 640 00:44:45,149 --> 00:44:46,207 the magnetic field in these magnets 641 00:44:46,450 --> 00:44:48,816 is about a thousand to 1500 gauss. 642 00:44:49,053 --> 00:44:50,111 So these have roughly the same 643 00:44:50,354 --> 00:44:53,653 magnetic field strength as a sunspot. 644 00:44:54,058 --> 00:44:56,026 They key difference of course is that a sunspot's 645 00:44:56,260 --> 00:44:58,023 an awful lot bigger and so the total energy, 646 00:44:58,228 --> 00:44:59,923 or the amount of energy in the magnetic field 647 00:45:00,097 --> 00:45:03,157 on the sun is enormous but the field strength 648 00:45:03,400 --> 00:45:06,801 at any given locationis something you can hold in your hand. 649 00:45:09,807 --> 00:45:13,334 Sun spots are just the visible effect of magnetic fields 650 00:45:13,577 --> 00:45:15,636 so strong that they can prevent the heat 651 00:45:15,879 --> 00:45:19,007 and light rising from the sun's interior. 652 00:45:24,321 --> 00:45:29,281 With the right viewing equipment you can even see the magnetic fields. 653 00:45:30,327 --> 00:45:33,660 Magnetic loops arch off the surface, 654 00:45:33,897 --> 00:45:36,661 like iron filings around a bar magnet they're shapes 655 00:45:36,900 --> 00:45:40,996 are mapped out by plasma heated to a million degrees. 656 00:45:41,205 --> 00:45:44,766 The largest are 200,000 kilometres high. 657 00:45:45,042 --> 00:45:48,034 And they are packed full of unstable energy. 658 00:45:49,046 --> 00:45:51,276 When you add up the total energy content 659 00:45:51,515 --> 00:45:54,780 in these loops it comes out to roughly 10 to the 21 joules 660 00:45:55,052 --> 00:45:59,284 of energy and that's roughly ten times the annual energy 661 00:45:59,523 --> 00:46:02,014 consumption of the united states. 662 00:46:02,626 --> 00:46:05,527 Of course we can see thousands of them at any one time. 663 00:46:11,301 --> 00:46:12,734 The loops are caused by the twisting 664 00:46:13,003 --> 00:46:16,131 of the sun's basic magnetic field. 665 00:46:19,009 --> 00:46:21,204 Because the sun rotates faster at the equator 666 00:46:21,445 --> 00:46:24,972 than at the poles it drags the field lines with it 667 00:46:25,149 --> 00:46:28,676 stretching and twisting them like elastic bands. 668 00:46:30,020 --> 00:46:32,989 As the solar cycle goes on the fields get more 669 00:46:33,190 --> 00:46:36,819 and more twisted and break through the surface. 670 00:46:38,729 --> 00:46:41,630 Until at Solar Max the whole sun is covered 671 00:46:41,865 --> 00:46:45,130 in loops stretched to breaking point. 672 00:46:47,838 --> 00:46:49,305 Solar flares are what happen 673 00:46:49,540 --> 00:46:53,442 when the strain gets too much and the loops snap. 674 00:46:56,680 --> 00:46:59,046 Basically all that energy comes out of the catastrophic 675 00:46:59,283 --> 00:47:03,049 release of energy that's been stored in the magnetic fields. 676 00:47:03,287 --> 00:47:05,687 So like if you wind up an elastic band too much, 677 00:47:05,989 --> 00:47:07,251 if you let it go with your fingers 678 00:47:07,491 --> 00:47:10,358 that elastic band flies across the room. 679 00:47:23,273 --> 00:47:26,674 When the energy bound within sunspots is released, 680 00:47:26,910 --> 00:47:32,177 billions of tonnes of plasma are fired far into space at huge speeds. 681 00:47:33,617 --> 00:47:38,077 And sometimes they are aimed straight forthe Earth. 682 00:47:42,226 --> 00:47:45,855 The flares fly through space for 2 days. 683 00:47:48,332 --> 00:47:49,629 When they reach us 684 00:47:49,867 --> 00:47:53,769 the earth's own magnetic field deflects most of the blow. 685 00:47:54,872 --> 00:47:57,306 But it is the impact on the magnetic field 686 00:47:57,541 --> 00:47:59,975 which causes the effects on Earth. 687 00:48:01,178 --> 00:48:06,445 It's called Space weather and the best of its effects are magical. 688 00:48:08,585 --> 00:48:12,214 The auroras dancing displays of celestial light 689 00:48:12,456 --> 00:48:15,653 are caused by particles from the solar storm smashing 690 00:48:15,893 --> 00:48:18,691 through the magnetic field at the poles. 691 00:48:21,798 --> 00:48:23,789 When they strike the upper atmosphere 692 00:48:24,034 --> 00:48:26,832 they light up the polar skies. 693 00:48:34,077 --> 00:48:36,238 In the strongest storms at the peak of the solar 694 00:48:36,480 --> 00:48:38,812 cycle the Northern lights can be seen 695 00:48:39,049 --> 00:48:42,143 as far south as Athens and Cuba. 696 00:48:45,255 --> 00:48:50,022 But the buffeting of the magnetic field has other unseen effects. 697 00:48:56,733 --> 00:49:00,100 Migratory animals that navigate using the magnetic field 698 00:49:00,337 --> 00:49:02,464 can lose their bearings. 699 00:49:04,074 --> 00:49:06,804 Racing pigeons don't come home. 700 00:49:11,515 --> 00:49:13,210 And whale strandings have been 701 00:49:13,450 --> 00:49:16,715 seen to increase with solar activity. 702 00:49:20,023 --> 00:49:22,548 But most worrying for us is the effect 703 00:49:22,793 --> 00:49:26,752 that the disrupted magnetic field can have on electronics. 704 00:49:35,439 --> 00:49:37,100 The strongest storms can damage 705 00:49:37,341 --> 00:49:41,744 or destroy satellites with devastating effects. 706 00:49:44,314 --> 00:49:46,179 We're sort of more sensitive to the sun 707 00:49:46,416 --> 00:49:49,749 than we probably realise because when the sun releases these, 708 00:49:50,020 --> 00:49:52,284 this magnetic energy in the form of solar flares and, 709 00:49:52,522 --> 00:49:54,217 and coronal mass ejections, 710 00:49:54,458 --> 00:49:57,256 maybe you don't notice it at first, but um, 711 00:49:57,494 --> 00:50:00,327 the crackle on your cell phone or your cell phone going out 712 00:50:00,564 --> 00:50:04,660 may actually be caused by enhanced activity on the sun. 713 00:50:11,575 --> 00:50:13,839 Mobile telephones, television, 714 00:50:14,077 --> 00:50:17,604 airplane navigation even weapons guidance systems 715 00:50:17,848 --> 00:50:20,373 all rely on satellite communication 716 00:50:20,617 --> 00:50:23,814 and all can be disturbed by space weather. 717 00:50:26,556 --> 00:50:28,888 The more we are reliant on these systems 718 00:50:29,126 --> 00:50:33,153 the more we will feel the effects of the sun's tantrums. 719 00:50:40,137 --> 00:50:44,437 But we still don't understand all of the effects of Space Weather. 720 00:50:46,309 --> 00:50:49,335 No-one can explain the effect on the climate. 721 00:50:50,047 --> 00:50:54,279 Or why the disappearance of sunspots should cause an ice age. 722 00:50:57,587 --> 00:50:59,248 It may not matter. 723 00:50:59,489 --> 00:51:02,754 The small effect that solar variation has on the climate 724 00:51:03,026 --> 00:51:07,827 has long since been drowned out by man-made global warming. 725 00:51:11,535 --> 00:51:13,264 As the world warms up, 726 00:51:13,503 --> 00:51:16,995 the sun may yet prove an unlikely source of cooling. 727 00:51:17,441 --> 00:51:21,673 The greenhouse effect could be stopped by harnessing its heat. 728 00:51:30,053 --> 00:51:32,578 The American Indians of the Southwest deserts 729 00:51:32,823 --> 00:51:35,121 have understood the importance of living sustainably 730 00:51:35,358 --> 00:51:38,486 with their environment for 100s of years. 731 00:51:41,665 --> 00:51:45,499 We have these natural disasters like the big old fires, 732 00:51:45,735 --> 00:51:47,134 the volcano's erupting, 733 00:51:47,370 --> 00:51:49,770 the big old earth quakes, the tsunami. 734 00:51:50,073 --> 00:51:53,531 That's the earth telling us that it's getting pretty tired. 735 00:51:53,910 --> 00:51:56,538 It's warning us that we need to slow down. 736 00:52:08,058 --> 00:52:09,821 On the Mesas of Arizona, 737 00:52:10,060 --> 00:52:14,895 far beyond the reach of the electricity grid lies Old Oraibi. 738 00:52:15,132 --> 00:52:18,226 The oldest occupied settlement in North America. 739 00:52:18,568 --> 00:52:22,004 For 1000 years the Hopi Indians have lived here in harmony 740 00:52:22,239 --> 00:52:24,002 with their environment. 741 00:52:29,045 --> 00:52:30,376 But that doesn't mean that they have to live 742 00:52:30,614 --> 00:52:33,583 without the conveniences of modern life. 743 00:52:33,817 --> 00:52:36,081 They have just realized that they are already 744 00:52:36,319 --> 00:52:38,844 getting all the power they need. 745 00:52:42,058 --> 00:52:44,253 Under the clear skies of the desert a family 746 00:52:44,494 --> 00:52:48,931 can be supplied with electricity from a couple of solar panels. 747 00:52:51,067 --> 00:52:53,331 Being that we pray to the sun every day, 748 00:52:53,570 --> 00:52:58,269 it's got our heart felt desires, he receives it every day, 749 00:52:59,442 --> 00:53:04,311 we thought the best source of energy should come from the sun. 750 00:53:08,385 --> 00:53:11,843 A few miles across the desert the idea is finally catching on 751 00:53:12,088 --> 00:53:14,852 with the rest of American civilization. 752 00:53:15,091 --> 00:53:18,652 But, naturally, it's on a much bigger scale. 753 00:53:22,098 --> 00:53:27,730 These are Stirling Dishes the Daddy of solar power systems. 754 00:53:28,038 --> 00:53:30,632 And they may be about to solve the energy crisis 755 00:53:30,874 --> 00:53:34,401 facing the cities of the American west. 756 00:53:36,046 --> 00:53:37,411 People want to run their air conditioners, 757 00:53:37,647 --> 00:53:39,842 their computers, their lights during the day 758 00:53:40,083 --> 00:53:42,483 and we run out of energy. 759 00:53:44,688 --> 00:53:47,282 We have a solar furnace 90million miles away 760 00:53:47,524 --> 00:53:49,549 that provides life for all of Earth. 761 00:53:49,793 --> 00:53:52,853 In the past we have been unable to harness that potential 762 00:53:53,096 --> 00:53:55,462 because the efficiency, the cost etc. 763 00:53:55,699 --> 00:53:57,360 Of the systems didn't make it viable 764 00:53:57,601 --> 00:53:59,569 what's changed is technology. 765 00:53:59,803 --> 00:54:03,295 The technology now allows us to build large scale, 766 00:54:03,540 --> 00:54:06,304 highly efficient, cost effective systems. 767 00:54:08,311 --> 00:54:12,213 Each dish tracks the movement of the sun across the sky, 768 00:54:12,449 --> 00:54:14,974 focusing the heat onto a single point. 769 00:54:15,151 --> 00:54:17,619 Where it is converted to electricity. 770 00:54:21,124 --> 00:54:25,151 They are twice as efficient as any other solar power system. 771 00:54:25,662 --> 00:54:28,290 With one you could power a small village. 772 00:54:28,531 --> 00:54:31,557 A fieldof them could power a city. 773 00:54:34,137 --> 00:54:36,628 Each system produces about 25 kw 774 00:54:36,873 --> 00:54:39,239 which is enough to power about 10 homes. 775 00:54:39,476 --> 00:54:42,138 However we plan to deploy these on a large scale. 776 00:54:42,379 --> 00:54:43,311 20,000 of these, 777 00:54:43,546 --> 00:54:45,844 which is massive about five hundred megawatts 778 00:54:46,082 --> 00:54:47,640 which is the equivalent to a coal fired plant, 779 00:54:47,884 --> 00:54:49,852 or maybe even a nuclear plant. 780 00:54:51,421 --> 00:54:53,582 The ink is just drying on the contract to 781 00:54:53,823 --> 00:54:57,020 build the first commercial solar power station. 782 00:54:59,095 --> 00:55:02,326 It will fill 5 square miles of the vast Californian desert 783 00:55:02,565 --> 00:55:05,398 with mirrors and will supply electricity 784 00:55:05,635 --> 00:55:07,967 to the city of San Diego. 785 00:55:08,138 --> 00:55:10,299 In time, as the technology and efficiency 786 00:55:10,540 --> 00:55:15,341 improves systems like these may spread around the world. 787 00:55:21,217 --> 00:55:23,481 These dishes are direct descendents 788 00:55:23,720 --> 00:55:27,588 of the stone monuments of Stonehenge and Orkney. 789 00:55:30,593 --> 00:55:33,858 Separated by 5000 years they all embody 790 00:55:34,097 --> 00:55:36,497 our desire to understand the sun, 791 00:55:36,733 --> 00:55:41,727 to be bathed in its light and to tap into its awesome power. 792 00:55:43,573 --> 00:55:47,805 He's quiet, he's clean, he's powerful. 793 00:55:48,778 --> 00:55:50,769 This was the way I was raised. 794 00:55:51,047 --> 00:55:57,111 Raised to respect him and to offer those prayers to him for keeping us 795 00:55:57,354 --> 00:55:59,447 for the length of time that he has. 796 00:55:59,689 --> 00:56:00,951 He's done this for generations, 797 00:56:01,191 --> 00:56:05,958 and generations and hopefully he will you know in the future. 798 00:56:09,733 --> 00:56:13,032 The sun will probably shine down on our civilisations 799 00:56:13,269 --> 00:56:15,567 for as long as they exist. 800 00:56:15,805 --> 00:56:18,330 If we survive for another billion years 801 00:56:18,575 --> 00:56:21,169 the sun will still be there. 802 00:56:25,014 --> 00:56:29,474 Butjust as the sun was once born, it will one day die. 803 00:56:29,719 --> 00:56:33,587 And when it does so, it will take the Earth with it. 804 00:56:36,159 --> 00:56:41,324 In about 5 billion years time the sun will run out of hydrogen. 805 00:56:44,734 --> 00:56:48,670 When it does it will become a red giant. 806 00:56:50,306 --> 00:56:53,332 Deprived of fuel the core will shrink. 807 00:56:53,576 --> 00:56:55,908 Generating so much heat that the outer layers 808 00:56:56,146 --> 00:56:58,842 will balloon into the solar system. 809 00:56:59,082 --> 00:57:01,983 The inner planets will be swept up. 810 00:57:04,687 --> 00:57:07,554 It may even swallow the Earth. 811 00:57:08,591 --> 00:57:13,028 Whether it is engulfed or not the Earth is doomed. 812 00:57:14,531 --> 00:57:18,365 The sun, burning 2000 times hotter than it does now 813 00:57:18,601 --> 00:57:22,128 will melt and seal the outer layers of the planet. 814 00:57:27,010 --> 00:57:30,468 Then suddenly the sun will stop burning. 815 00:57:34,350 --> 00:57:38,184 As the remains of the solar system is plunged into darkness 816 00:57:38,421 --> 00:57:42,050 the sun's core will collapse and with its last gasp it 817 00:57:42,292 --> 00:57:46,490 will blow its remaining shroud of gas into space. 818 00:57:48,298 --> 00:57:51,495 It will be forever night. 819 00:57:51,835 --> 00:57:55,635 The story of the sun and the earth will have ended. 820 00:57:55,872 --> 00:57:59,000 And a small part of the outer arm of the Milky Way 821 00:57:59,175 --> 00:58:01,700 will be a little bit darker. 822 00:58:03,313 --> 00:58:06,248 But around it in the rest of the universe 823 00:58:06,483 --> 00:58:08,610 the same story will be being told 824 00:58:08,852 --> 00:58:12,549 by a billion other small insignificant stars 825 00:58:12,789 --> 00:58:16,691 twinkling in the vastness of space.