0:00:07 > 0:00:15It is dawn and the sun is rising, as it has every day for the last five billion years.
0:00:15 > 0:00:24For millennia it has been a constant golden disk shining its unchanging light onto the Earth.
0:00:24 > 0:00:29But look through the glare and the true face of the sun is revealed.
0:00:29 > 0:00:32Not constant, but constantly changing.
0:00:33 > 0:00:37Turbulent and violent.
0:00:37 > 0:00:41Its worst tantrums can wreak havoc on the Earth.
0:00:41 > 0:00:49To understand the sun is to understand the forces that drive the universe.
0:00:49 > 0:00:54If we can control those forces, we can unlock the power of the stars.
0:00:57 > 0:01:00The power of our sun.
0:01:10 > 0:01:15The story of the sun starts 13 billion years ago with the big bang.
0:01:19 > 0:01:27In an instant, the universe was born, and since then it's been expanding at the speed of light.
0:01:27 > 0:01:31Within the universe there are 100 billion galaxies.
0:01:31 > 0:01:34Our galaxy is but one of them.
0:01:34 > 0:01:37In it, there are 100 billion stars.
0:01:37 > 0:01:43And towards the edge of one of the spiral arms is an almost insignificant dot.
0:01:43 > 0:01:48A medium-sized, not very bright, undistinguished star.
0:01:50 > 0:01:54Up close, it's a different story.
0:01:54 > 0:02:01On the planets closest to the sun, Mercury and Venus, the heat is intense, their surfaces scorched.
0:02:05 > 0:02:09Further out through the solar system, the sun's rays weaken,
0:02:09 > 0:02:13until they are powerless against the chill of space.
0:02:15 > 0:02:17The outer planets are frozen.
0:02:19 > 0:02:23But in the middle lies the Goldilocks planet.
0:02:23 > 0:02:26Not too hot, and not too cold.
0:02:26 > 0:02:32In fact it's just right, and life has flourished in the warm glow.
0:02:39 > 0:02:44All life on Earth owes its existence to the sun.
0:02:44 > 0:02:49It powers every natural system and sustains every plant and animal.
0:02:53 > 0:02:58Without the sun, the planet would be a barren, lifeless ball of rock.
0:03:00 > 0:03:05Recognising that power, humans have always worshipped the sun.
0:03:07 > 0:03:11But we have also always striven to understand it.
0:03:16 > 0:03:19These monuments are more than just temples.
0:03:19 > 0:03:22They are calendars and observatories.
0:03:22 > 0:03:24Tools for studying the sun.
0:03:27 > 0:03:30Some of them are still operational.
0:03:36 > 0:03:38This is Orkney.
0:03:38 > 0:03:42To live here is to know the importance of the sun.
0:03:42 > 0:03:46In the summer, the days are long and full of light.
0:03:49 > 0:03:53In December it's a different story.
0:03:53 > 0:03:55It's mid-winter.
0:03:55 > 0:03:59It's about 11 in the morning and it's still not light completely.
0:03:59 > 0:04:05There's a strong wind coming off the Atlantic and it's cold and it's wet.
0:04:05 > 0:04:09That's pretty much typical of this time of the year up here.
0:04:16 > 0:04:23Yet, despite the cold, in the Stone Age, 5000 years ago, a civilisation thrived here.
0:04:23 > 0:04:26The island is covered in the remains of their society.
0:04:29 > 0:04:32The ruins are full of mystery.
0:04:32 > 0:04:35We know little about the people who lived here,
0:04:35 > 0:04:41but they did leave evidence of the important role the sun played in their lives.
0:04:42 > 0:04:46Maeshowe, 1,000 years older than the Pyramids,
0:04:46 > 0:04:49is one of finest examples of Stone Age architecture.
0:04:51 > 0:04:54Entering Maeshowe,
0:04:54 > 0:04:58you have to crouch right down and are confronted with a passage
0:04:58 > 0:05:02that seems to go on and on and on.
0:05:02 > 0:05:07Slightly feel an impression of going uphill, up a slope.
0:05:07 > 0:05:10Coming through clearly another doorway,
0:05:11 > 0:05:13suddenly...
0:05:13 > 0:05:18the whole thing opens out into the most amazing chamber.
0:05:18 > 0:05:22This alone is probably the highest and largest enclosed space
0:05:22 > 0:05:26that Neolithic Orcadians would have experienced.
0:05:27 > 0:05:31When it was excavated, back in the 19th century,
0:05:31 > 0:05:37the clay floor was littered with broken pieces of human skull.
0:05:37 > 0:05:39This is a place of the dead.
0:05:39 > 0:05:41This is a house of the dead.
0:05:45 > 0:05:49Most of the time the occupants of the tomb were left in complete darkness.
0:05:53 > 0:05:56Then, at sunset on the Winter Solstice,
0:05:56 > 0:05:59the shortest day of the year, something amazing happens.
0:06:07 > 0:06:11The light of the setting sun shines straight up the entrance tunnel
0:06:11 > 0:06:13and illuminates the interior.
0:06:14 > 0:06:22The significance is that it's marking the shortest time of the year, with the least light,
0:06:22 > 0:06:24and from that point on, slowly and gradually,
0:06:24 > 0:06:28light is going to increase, the days are going to grow longer.
0:06:28 > 0:06:33So what's happening here is that the dead, the ancestors,
0:06:33 > 0:06:36are being awoken on that shortest day.
0:06:40 > 0:06:44The Winter Solstice events at Maeshowe demonstrate
0:06:44 > 0:06:48an intimate and precise knowledge of the sun's movements through the sky.
0:06:51 > 0:06:54It was the first step on our journey
0:06:54 > 0:06:57to understand the sun and its many effects on us.
0:06:59 > 0:07:02To complete that journey, we've had to travel
0:07:02 > 0:07:04to the furthest depths of space
0:07:04 > 0:07:06and to the heart of the smallest atom.
0:07:09 > 0:07:12And with every closer look, the sun has always surprised us.
0:07:15 > 0:07:20To our ancestors, its power was its reliability.
0:07:20 > 0:07:21Always on time.
0:07:21 > 0:07:23Never changing.
0:07:26 > 0:07:30But the reality is proving to be very different.
0:07:30 > 0:07:35Most people think of the sun as quite a boring, constant sort of thing, but it's not at all.
0:07:35 > 0:07:37It's changing all the time.
0:07:37 > 0:07:40If you look, you can changes in a matter of minutes or hours.
0:07:40 > 0:07:43It's far from static and boring.
0:07:43 > 0:07:46It's changing and it's got a life of its own.
0:07:47 > 0:07:51Modern solar observatories magnify and filter the sun's light
0:07:51 > 0:07:56to get past the constant glare and give a clear view of the surface.
0:08:06 > 0:08:10This is the actual face of the sun.
0:08:11 > 0:08:14It is turbulent and boiling.
0:08:14 > 0:08:16Never the same from one second to the next,
0:08:16 > 0:08:19the surface bubbles like a giant bowl of porridge.
0:08:27 > 0:08:31Each bubble is 1,000 miles across.
0:08:34 > 0:08:40The heat and light brought to the surface raises its temperature to 6,000 degrees centigrade -
0:08:40 > 0:08:43enough to vaporise solid rock.
0:08:46 > 0:08:48And the sun is huge.
0:08:48 > 0:08:52You could fit the Earth inside it a million times over.
0:08:54 > 0:08:59Periodically, huge explosions rip through the surface,
0:08:59 > 0:09:04releasing the energy of a billion atomic bombs in seconds.
0:09:04 > 0:09:07All this is on the surface.
0:09:07 > 0:09:13To understand the sun, we must know what is going on deep inside.
0:09:13 > 0:09:16That is where the power is generated.
0:09:26 > 0:09:30So, for centuries, scientists have been devising ways
0:09:30 > 0:09:33to probe the heart of the sun.
0:09:33 > 0:09:37Some of them have been complex and some of them very simple.
0:09:41 > 0:09:45And the first step is to figure out just how powerful the sun is.
0:09:47 > 0:09:50It's easy to appreciate the power of the sun
0:09:50 > 0:09:54on a nice hot summer's day on the Texas Gulf Coast.
0:09:54 > 0:09:57You feel the power of the sun on your skin, sunscreen's on.
0:09:57 > 0:09:59But, man, the sun is just...
0:09:59 > 0:10:02the actual physics of what's going on inside the sun,
0:10:02 > 0:10:06the power of the sun, the energy it's releasing,
0:10:06 > 0:10:08is almost beyond comprehension.
0:10:09 > 0:10:13But it is only almost beyond comprehension.
0:10:15 > 0:10:20And you can measure its power output with some simple apparatus.
0:10:20 > 0:10:24One of the earliest experiments to measure the power of the sun
0:10:24 > 0:10:27was by astronomer William Herschel in the 19th century,
0:10:27 > 0:10:32where he had the brilliant idea of watching ice melt to see how long it would take.
0:10:32 > 0:10:35Therefore, from the properties of the ice,
0:10:35 > 0:10:38he worked out how much sunlight was coming to the ground.
0:10:46 > 0:10:49As a demonstration of the sun's power,
0:10:49 > 0:10:51it doesn't look that impressive.
0:10:51 > 0:10:55But Hershel realized that he could use the time it takes to melt one bit of ice
0:10:55 > 0:10:59to calculate the sun's total power output.
0:11:01 > 0:11:04So here we see the ice is almost completely melted
0:11:04 > 0:11:07in roughly 29 minutes - almost half an hour.
0:11:07 > 0:11:11Herschel was able to use this experiment and the time that it took to melt the ice
0:11:11 > 0:11:13to work out basic properties of the sun.
0:11:14 > 0:11:18Here's how Herschel's thinking worked.
0:11:18 > 0:11:21In the time it takes to melt a slab of ice on Earth,
0:11:21 > 0:11:24the sun is radiating heat in all directions -
0:11:24 > 0:11:27enough to melt a complete shell of ice around it,
0:11:27 > 0:11:30a diameter of 300 million kilometres.
0:11:30 > 0:11:32A shell half a centimetre thick
0:11:32 > 0:11:36and 300 million kilometres across contains a lot of ice -
0:11:36 > 0:11:40enough to make an ice cube bigger than the Earth.
0:11:40 > 0:11:43To melt that much ice in just 30 minutes
0:11:43 > 0:11:48would take an energy input of a billion billion billion watts.
0:11:49 > 0:11:53It's a rough but surprisingly accurate experiment.
0:11:53 > 0:11:57Modern satellite readings confirm the figures to within a few percent.
0:12:00 > 0:12:04It's an almost unimaginable amount of energy.
0:12:04 > 0:12:08If we could harness the sun's power output for a single second,
0:12:08 > 0:12:13it would satisfy the world's energy demands for the next million years.
0:12:17 > 0:12:20But it's one thing to know how much power the sun is producing.
0:12:20 > 0:12:23It's something else to know how it's doing it.
0:12:25 > 0:12:27Until the middle of the 20th century,
0:12:27 > 0:12:30no-one had any idea what made the sun work.
0:12:30 > 0:12:34For scientists in Hershel's time, it was a mystery.
0:12:36 > 0:12:39One of the issues was what powered the sun.
0:12:39 > 0:12:43And some very clever people actually considered the fact
0:12:43 > 0:12:45that the sun might be powered by burning coal.
0:12:45 > 0:12:48It seems ludicrous, but why not coal?
0:12:48 > 0:12:51That was an important source of energy on the Earth
0:12:51 > 0:12:54in that part of the 19th century.
0:12:59 > 0:13:02If the sun was made entirely of coal,
0:13:02 > 0:13:05there would be one unfortunate consequence.
0:13:06 > 0:13:10It would burn itself out in just a few thousand years.
0:13:13 > 0:13:16Today that sounds ridiculous,
0:13:16 > 0:13:20but 200 years ago, it didn't seem so unlikely.
0:13:22 > 0:13:24It was widely believed that the Earth
0:13:24 > 0:13:27was only a few thousand years old.
0:13:32 > 0:13:36But in the mid 19th century, a new science was emerging
0:13:36 > 0:13:40that was painting a very different picture of the age of the Earth.
0:13:43 > 0:13:46By looking at the deepest layers of rocks,
0:13:46 > 0:13:50geologists were discovering that the Earth was much older
0:13:50 > 0:13:53than anyone had previously imagined.
0:13:53 > 0:13:55If that was true,
0:13:55 > 0:13:59then the sun also had to have been burning for much, much longer.
0:13:59 > 0:14:03You can see the strata and the lines in the rock
0:14:03 > 0:14:08that represent hundreds of millions of years of geological history.
0:14:08 > 0:14:10The top of Sacramento Peak, up beyond this,
0:14:10 > 0:14:13we find fossils that are 300 million years old.
0:14:13 > 0:14:17Below Sacramento Peak you've got more than a kilometre of strata
0:14:17 > 0:14:19that are far older than that.
0:14:19 > 0:14:22From the age of these strata, geologists knew that the Earth
0:14:22 > 0:14:25was at least a billion years old.
0:14:25 > 0:14:27At the same time,
0:14:27 > 0:14:30astronomers thought the sun was only 10,000 years old.
0:14:30 > 0:14:37If geologists were right, astronomers had to find another source for the sun producing its energy.
0:14:41 > 0:14:43The search for the source of energy
0:14:43 > 0:14:46that could power the sun for billions of years
0:14:46 > 0:14:48lasted for nearly a century.
0:14:50 > 0:14:53Eventually, scientists would find the answer
0:14:53 > 0:14:57in the forces that hold atoms together,
0:14:57 > 0:14:59and in the nature of matter itself.
0:14:59 > 0:15:03But first, you have to know what the sun is made of.
0:15:05 > 0:15:10To find that out, you need to take a very close look at sunlight.
0:15:19 > 0:15:23When you take the light from the sun and pass it through a prism,
0:15:23 > 0:15:25spread it out into the colours,
0:15:25 > 0:15:29you notice it isn't uniform - there are places that are darker.
0:15:29 > 0:15:32Each of those dark lines is due to a specific chemical element.
0:15:32 > 0:15:36Each element has its own series of lines that are specific to it.
0:15:38 > 0:15:43Each chemical element absorbs light at specific frequencies,
0:15:43 > 0:15:46removing a strip from the spectrum.
0:15:46 > 0:15:49As the light passes through the sun,
0:15:49 > 0:15:51all the elements leave their mark.
0:15:51 > 0:15:54So, when the light arrives at the Earth,
0:15:54 > 0:15:57it contains the complete chemical formula of the sun.
0:16:01 > 0:16:04If we take the spectrum and spread it out to fine details -
0:16:04 > 0:16:09and what we've done here is stacked up pieces of the spectrum on top of each other -
0:16:09 > 0:16:11you see all of these dark areas.
0:16:11 > 0:16:14The key to figuring out how much of these elements are there
0:16:14 > 0:16:17is the breadth and the depth of the line -
0:16:17 > 0:16:19how dark is the line and how broad is it?
0:16:23 > 0:16:27The composition of the sun lies in this barcode.
0:16:29 > 0:16:33All the thin lines are caused by tiny amounts of complex elements -
0:16:33 > 0:16:35metals like iron and magnesium.
0:16:35 > 0:16:38But there are three very deep, broad lines,
0:16:38 > 0:16:43and they are all caused by an enormous amount of a single element.
0:16:46 > 0:16:50There's some helium and traces of heavier elements.
0:16:50 > 0:16:54But over 90% of the sun is hydrogen.
0:16:59 > 0:17:05It's the simplest and most common element in the universe.
0:17:05 > 0:17:09The secrets of the sun's power must lie in this gas.
0:17:13 > 0:17:15Look carefully into the night sky,
0:17:15 > 0:17:20and you'll see clouds of hydrogen floating in interstellar space.
0:17:23 > 0:17:29These are nebulae, and they can be hundreds of light years across.
0:17:35 > 0:17:38They are some of the brightest areas in the sky,
0:17:38 > 0:17:43lit up by the intense light of newly-formed massive stars.
0:17:43 > 0:17:47In them, we can see stars being born.
0:17:50 > 0:17:53It's to areas like this that astronomers turn their telescopes
0:17:53 > 0:17:57when they want to study how our sun was formed.
0:17:58 > 0:18:00There she is. OK.
0:18:00 > 0:18:03So let's re-centre on her.
0:18:09 > 0:18:11By studying different nebulae,
0:18:11 > 0:18:15it's possible to piece together the stages in which stars are made.
0:18:21 > 0:18:24And it all starts in a cold, dark cloud,
0:18:24 > 0:18:27floating around waiting for something to happen.
0:18:29 > 0:18:32Cold clouds like this are actually quite stable.
0:18:32 > 0:18:34They will sit there for a very long time,
0:18:34 > 0:18:36for thousands or millions of years,
0:18:36 > 0:18:39before they will actually do anything.
0:18:39 > 0:18:43What you need to get the star formation process going is to kick it with something.
0:18:45 > 0:18:50That can be an impact on the cloud from one side by a supernova blast wave -
0:18:50 > 0:18:55a massive star nearby has gone phoom at the end of its life,
0:18:55 > 0:19:00and that sends out in all directions very energetic compression waves
0:19:00 > 0:19:03that hit the gas and compress it.
0:19:05 > 0:19:08The shock waves knock the cloud out of balance,
0:19:08 > 0:19:11causing localised clumps of hydrogen to form.
0:19:13 > 0:19:16These are the seeds from which stars grow.
0:19:18 > 0:19:23The increased gravity of the seeds sucks in more and more hydrogen
0:19:23 > 0:19:27in a runaway process that lasts for a million years.
0:19:29 > 0:19:35As more hydrogen is squeezed into the clumps, the temperature rises.
0:19:36 > 0:19:39They are not yet producing light,
0:19:39 > 0:19:43but they are well on their way to becoming stars.
0:19:43 > 0:19:46As they grow bigger and bigger, they start to spin
0:19:46 > 0:19:51and throw out a disk of debris that coalesces to form a solar system.
0:19:53 > 0:19:58This kind of process is exactly what would have formed our solar system.
0:19:58 > 0:20:01When we look at our solar system,
0:20:01 > 0:20:05all of the planets rotate around the sun in the same direction,
0:20:05 > 0:20:10and they all are in the same plane - the same flat sheet around our sun -
0:20:10 > 0:20:13and this is exactly a consequence of the fact
0:20:13 > 0:20:18that the early solar system formed out of a broad disc.
0:20:19 > 0:20:22With the solar system in place,
0:20:22 > 0:20:25all that is left is for the young star to light up.
0:20:25 > 0:20:29When it happens, it is sudden and irreversible.
0:20:31 > 0:20:34Ultimately, the process starts.
0:20:38 > 0:20:42And because it liberates so much energy with that first fusion,
0:20:42 > 0:20:45then the process takes off.
0:20:45 > 0:20:48It lights up a large area
0:20:48 > 0:20:51and it starts to shine on its own within a matter of minutes.
0:20:51 > 0:20:52It's a very quick process.
0:20:56 > 0:20:58In that first burst of light,
0:20:58 > 0:21:01the star has begun its lifelong activity
0:21:01 > 0:21:04as a factory for making other chemical elements.
0:21:07 > 0:21:12Every atom in everything around us was made in the heart of a star,
0:21:12 > 0:21:15and all were made from the same starting ingredient.
0:21:20 > 0:21:23The simplest element that we have is hydrogen,
0:21:23 > 0:21:28and it's the building block for all the other elements that we have.
0:21:30 > 0:21:35In the heart of the sun, hydrogen nuclei - protons -
0:21:35 > 0:21:38are stuck together to make helium.
0:21:38 > 0:21:40It sounds straightforward,
0:21:40 > 0:21:44but it can only happen in the most extreme conditions.
0:21:44 > 0:21:46In order for these protons to come together,
0:21:46 > 0:21:48because they're both positively charged -
0:21:48 > 0:21:51they've actually go to be pushed together.
0:21:51 > 0:21:55In order to do this, you need very high temperatures -
0:21:55 > 0:21:59so they're moving very fast, and you also need very high pressures.
0:22:01 > 0:22:06The only part of the sun that is hot and dense enough is the core -
0:22:06 > 0:22:09an area that contains over half the star's mass
0:22:09 > 0:22:11in less than 2% of its volume.
0:22:14 > 0:22:16Here, at 15 million degrees,
0:22:16 > 0:22:21the protons are bashed together so hard that they fuse.
0:22:23 > 0:22:25A helium nucleus is a tiny bit lighter
0:22:25 > 0:22:30than the combined mass of the four protons it is made from.
0:22:33 > 0:22:35And, as Einstein tells us,
0:22:35 > 0:22:39it is that tiny bit of lost mass that provides the power.
0:22:41 > 0:22:45Energy is equal to mass times the speed of light,
0:22:45 > 0:22:47times the speed of light.
0:22:47 > 0:22:50Now, the speed of light is a very, very big number.
0:22:50 > 0:22:54So, if we take a small amount of mass, we get a huge amount of energy.
0:22:54 > 0:22:57That's the energy which powers our sun.
0:22:59 > 0:23:05Every second, five million tonnes of the sun is converted to pure energy.
0:23:05 > 0:23:08And although it has been burning for five billion years,
0:23:08 > 0:23:13it is only halfway through its supplies of hydrogen.
0:23:13 > 0:23:18The light produced in the core must travel over half a million kilometres to the surface.
0:23:18 > 0:23:20And it does so very slowly.
0:23:20 > 0:23:23The heart of the sun is so dense,
0:23:23 > 0:23:26the speed of light is less than 1mm a second.
0:23:28 > 0:23:30It can take 200,000 years
0:23:30 > 0:23:35for the light to travel from the core to the surface.
0:23:35 > 0:23:39It takes just another eight minutes to get to the Earth.
0:23:45 > 0:23:48This is what the power of nuclear fusion looks like
0:23:48 > 0:23:51from 150 million kilometres away.
0:23:55 > 0:23:58This is what it looks like close up.
0:24:01 > 0:24:06The H-bomb was man's first attempt at recreating the sun on Earth -
0:24:06 > 0:24:10a balloon full of hydrogen squeezed until it released its energy.
0:24:18 > 0:24:21In contrast to its destructive power,
0:24:21 > 0:24:24it's long been realised that controlled nuclear fusion
0:24:24 > 0:24:27could solve the world's energy problems.
0:24:29 > 0:24:34It has been one of the holy grails of science for half a century.
0:24:37 > 0:24:42This kind of power, the H-bomb, is a manmade version of this - the sun.
0:24:42 > 0:24:47In 1958, Britain announced that she could produce this power in a laboratory,
0:24:47 > 0:24:49in a machine called Zeta.
0:24:49 > 0:24:54There is a prospect of unlimited energy from controlled thermo-nuclear fusion.
0:24:55 > 0:24:58Unfortunately, it wasn't that easy.
0:24:59 > 0:25:03But now, nearly 50 years later,
0:25:03 > 0:25:06in the same laboratories in Oxfordshire,
0:25:06 > 0:25:10scientists are finally managing to create their own star on Earth.
0:25:19 > 0:25:22- Ready when you are.- OK, ready.
0:25:26 > 0:25:29Requiring shot 14658.
0:25:35 > 0:25:38Starting shot in five seconds.
0:25:46 > 0:25:49It might not seem like much...
0:25:51 > 0:25:57..but slowed down by 300 times, the pictures reveal how the gas plasma
0:25:57 > 0:25:59is being squeezed and heated
0:25:59 > 0:26:03to create the most extreme conditions in the solar system.
0:26:06 > 0:26:10Plasmas I always like to think of as being like naughty children.
0:26:10 > 0:26:14They're full of energy and they want to misbehave,
0:26:14 > 0:26:18and it's our job to try and control that misbehaviour.
0:26:20 > 0:26:23For the particles to fuse on Earth,
0:26:23 > 0:26:25the temperatures need to be raised
0:26:25 > 0:26:29to ten times those found at the heart of the sun.
0:26:30 > 0:26:33Bombarding the gas with a stream of fast neutrons
0:26:33 > 0:26:37raises the temperature to over 100 million degrees.
0:26:39 > 0:26:44Only then can the energy of nuclear fusion be released.
0:26:45 > 0:26:50After years of learning to control the plasma, scientists now believe
0:26:50 > 0:26:54they are within sight of harnessing the sun's power.
0:26:58 > 0:27:03The aim of it is to be able to produce cheap, clean
0:27:03 > 0:27:08and effectively an inexhaustible supply of electricity for future generations.
0:27:09 > 0:27:13This is only a small experimental reactor.
0:27:13 > 0:27:15It can only run for a few seconds
0:27:15 > 0:27:18and sucks up more energy than it creates.
0:27:20 > 0:27:24But the next generation of bigger reactors is already being built.
0:27:26 > 0:27:31When operational, they will produce ten times more energy than they use.
0:27:31 > 0:27:33They will be stars on Earth -
0:27:33 > 0:27:37power stations that won't deplete natural resources,
0:27:37 > 0:27:40or produce dangerous waste products.
0:27:40 > 0:27:45It sounds great, but recreating the sun isn't easy
0:27:45 > 0:27:47and it may be another 50 years
0:27:47 > 0:27:51before the fusion power station becomes reality.
0:27:58 > 0:28:03Until then, we'll just have to make do with the real thing.
0:28:03 > 0:28:05But that's not so bad.
0:28:05 > 0:28:08Just seeing sunlight is enough to cheer us up.
0:28:12 > 0:28:15Many people think it's the warmth of the sun
0:28:15 > 0:28:18that is associated with us feeling good.
0:28:18 > 0:28:21Of course that's true, but research has shown
0:28:21 > 0:28:25it's not really the warmth - it's the light that's important.
0:28:26 > 0:28:29Sunlight controls our daily cycle,
0:28:29 > 0:28:34making sure we wake up in the morning and go to sleep at night.
0:28:41 > 0:28:45When there's not enough light those patterns get disturbed,
0:28:45 > 0:28:47with miserable effect.
0:28:48 > 0:28:52It's a clinical fact that depression is more common in winter
0:28:52 > 0:28:54because of the lack of sunlight.
0:28:54 > 0:28:58They call it SAD - Seasonal Affective Disorder.
0:29:01 > 0:29:04Seasonal Affective Disorder is a depressive illness.
0:29:04 > 0:29:08It the starts during the autumn and early winter
0:29:08 > 0:29:12and usually goes away completely during spring and early summer.
0:29:13 > 0:29:17Some people feel quite miserable, depressed and gloomy
0:29:17 > 0:29:21during the winter months and some people - a small proportion -
0:29:21 > 0:29:25will go on to develop clinically significant depression,
0:29:25 > 0:29:27which requires treatment.
0:29:38 > 0:29:42This is Rattenburg, a fairytale Austrian village
0:29:42 > 0:29:44cursed by a lack of sunlight.
0:29:46 > 0:29:48Due to a quirk of geology,
0:29:48 > 0:29:53it gets no sunlight at all between November and February.
0:29:53 > 0:29:58During those winter months, the sun never rises high enough
0:29:58 > 0:30:01to clear the brow of Rat Mountain.
0:30:02 > 0:30:05And the town lies in permanent shadow,
0:30:05 > 0:30:10while it's neighbour across the river basks in the sunshine.
0:30:10 > 0:30:12In winter, of course, it's very cold.
0:30:12 > 0:30:17It's shadow and, as you can imagine, it's cold.
0:30:17 > 0:30:22We are freezing and if you want to have some sun, you have to move to the next village.
0:30:22 > 0:30:25It makes you happier to sit in the sunlight
0:30:25 > 0:30:28and not to freeze in the shadow.
0:30:30 > 0:30:34Frozen and in the dark, the residents have been forced
0:30:34 > 0:30:39to take desperate measures to bring some light into their lives.
0:30:43 > 0:30:46Helmar Zangirl is a lighting expert who specialises
0:30:46 > 0:30:50in bringing natural light into some of the world's biggest buildings.
0:30:50 > 0:30:55He may be the salvation of Rattenburg.
0:30:57 > 0:30:59Evolutionary speaking,
0:30:59 > 0:31:01man has adapted to natural light,
0:31:01 > 0:31:07and has adapted to the sun, and if you deprive man of the sun,
0:31:07 > 0:31:11clearly it's a different quality of life.
0:31:13 > 0:31:18How do you feel if you sit for one week in a place with fog?
0:31:18 > 0:31:23And how do you feel if you sit for one day in a place where the sun shines?
0:31:23 > 0:31:27I personally feel so much happier in sunshine, I can tell you that.
0:31:31 > 0:31:33The solution for Rattenburg is simple -
0:31:33 > 0:31:37steal some of the sunlight from the other side of the valley.
0:31:39 > 0:31:43Eventually, a huge system of mirrors will reflect the light of the sun
0:31:43 > 0:31:47to a second set of mirrors on the castle above the town,
0:31:47 > 0:31:49and then reflect it down into the streets
0:31:49 > 0:31:54to brighten the lives of the citizens of Rattenburg.
0:31:54 > 0:31:57The main effect for the people in town will be
0:31:57 > 0:32:00that part of the facades of buildings
0:32:00 > 0:32:03and parts of the street, at least of the main street,
0:32:03 > 0:32:05will be brightly illuminated,
0:32:05 > 0:32:08and will clearly be recognised as sunlight.
0:32:13 > 0:32:16It sounds crazy, but it's true.
0:32:16 > 0:32:20People will go to extraordinary lengths for a bit of sunlight.
0:32:25 > 0:32:28But the sun is much more than a giant light bulb.
0:32:31 > 0:32:34There are other forces at work in the sun.
0:32:38 > 0:32:42Forces that change over minutes and over years.
0:32:43 > 0:32:47Forces that tear the surface apart.
0:32:47 > 0:32:51We are only now beginning to understand these forces
0:32:51 > 0:32:53and the effects they have on the Earth.
0:32:53 > 0:32:57But we've known about them for hundreds of years...
0:32:57 > 0:33:00because the sun gets spots.
0:33:03 > 0:33:06Sun spots are dark regions on the surface of the sun,
0:33:06 > 0:33:10typically about the size of the Earth, in terms of area.
0:33:10 > 0:33:13Here's a live shot of one today.
0:33:13 > 0:33:18Unfortunately, we've got a very windy day with high thin clouds, so the picture's not very sharp.
0:33:18 > 0:33:22With very high resolution images, we can see detailed structure.
0:33:42 > 0:33:45The inner part of the sun spot, the dark umbra,
0:33:45 > 0:33:49is dark only in comparison to the rest of the Sun.
0:33:49 > 0:33:54It's actually bright enough to blind you if you looked at it alone.
0:33:55 > 0:33:58The spots are not static.
0:33:58 > 0:34:02These video images show the edges crawling,
0:34:02 > 0:34:05almost as if it was alive.
0:34:20 > 0:34:25The movements of sun spots have been studied for 400 years,
0:34:25 > 0:34:29ever since Galileo trained his telescope on the sun
0:34:29 > 0:34:32and made the first crucial discovery about its behaviour.
0:34:34 > 0:34:38Surprised to see black dots creeping over the surface,
0:34:38 > 0:34:41he kept track of them over a number of days,
0:34:41 > 0:34:44and found that they were all moving in the same direction.
0:34:48 > 0:34:51To Galileo, the meaning was clear -
0:34:51 > 0:34:53the sun was rotating,
0:34:53 > 0:34:57and was turning faster at the equator than at the poles.
0:34:58 > 0:35:03It was a discovery that was to prove critical in our understanding of how the sun works.
0:35:05 > 0:35:07Ever since Galileo,
0:35:07 > 0:35:12records have been kept of the coming and goings of sun spots
0:35:12 > 0:35:14and variations soon became clear.
0:35:14 > 0:35:18Sometimes the sun is covered in hundreds of spots.
0:35:18 > 0:35:21Other times, there are none at all.
0:35:21 > 0:35:25And after a while, a pattern emerged.
0:35:26 > 0:35:29If you observe sun spots over several years,
0:35:29 > 0:35:32they come and go with about an 11-year cycle.
0:35:32 > 0:35:37From a minimum, where there can be no spots at all on the sun for weeks or months at a time,
0:35:37 > 0:35:42to a maximum where you can have 100 spots visible on the surface of the sun,
0:35:42 > 0:35:47and then a decline again, usually over about six years or so, back to minimum.
0:35:50 > 0:35:54Until recently, no-one knew what was driving the solar cycle.
0:35:54 > 0:35:56Or where sun spots came from.
0:36:00 > 0:36:04But people had always suspected that the scars on the sun's surface
0:36:04 > 0:36:06had an effect on the Earth.
0:36:06 > 0:36:10But no-one could quite put their finger on what it was.
0:36:10 > 0:36:14It has been correlated with all kinds of different things -
0:36:14 > 0:36:18the price of wheat, the thickness of fur on animals.
0:36:18 > 0:36:23I get a guy that comes to my website trying to predict the stock market
0:36:23 > 0:36:26from the daily sun spot areas.
0:36:26 > 0:36:29"Oh, you didn't post them today! I gotta know!"
0:36:29 > 0:36:33"You making money or what?! I want some if you are!"
0:36:37 > 0:36:42One effect sun spots do have on the Earth is on the climate.
0:36:43 > 0:36:46But it is a subtle effect.
0:36:46 > 0:36:51Its greatest impact was only noticed 300 years after the event.
0:36:56 > 0:37:00It was discovered in Greenwich by the astronomer Robert Maunder,
0:37:00 > 0:37:04who was studying the hundreds of years of sun spot records
0:37:04 > 0:37:06held at the Royal Observatory.
0:37:10 > 0:37:12In the late part of the 19th century,
0:37:12 > 0:37:16he became particularly interested in sun spots.
0:37:16 > 0:37:21He discovered there had been a peculiar effect in the second part of the 17th and 18th centuries
0:37:21 > 0:37:25when sun spot numbers diminished to a fraction of what they are today.
0:37:25 > 0:37:28He described this as the Maunder Minimum.
0:37:32 > 0:37:38For 70 years, from 1645-1715,
0:37:38 > 0:37:40sun spots disappeared.
0:37:40 > 0:37:44It was as if the engine that drives the solar cycle had stopped.
0:37:44 > 0:37:47And it correlated almost exactly
0:37:47 > 0:37:50with the last period of prolonged cold
0:37:50 > 0:37:52to strike the northern hemisphere.
0:37:52 > 0:37:55They call it the little ice age.
0:37:59 > 0:38:02What's interesting about a period like the little ice age
0:38:02 > 0:38:05is that you don't see a very large dip in temperatures
0:38:05 > 0:38:09but even a degree or two is enough to see some really quite dramatic effects.
0:38:09 > 0:38:12Like pack ice advancing south from the North Pole,
0:38:12 > 0:38:16like the Viking colonies in Greenland being wiped out by the changing climate
0:38:16 > 0:38:19and the population of Iceland falling by half.
0:38:21 > 0:38:24In Britain, the weather was cold enough
0:38:24 > 0:38:26the Thames would freeze in winter,
0:38:26 > 0:38:30and one of the classic depictions of life at the time is frost fairs,
0:38:30 > 0:38:32when the population held a fair on the frozen river.
0:38:32 > 0:38:35So things must have been a lot harsher than today.
0:38:42 > 0:38:45When the sun spots disappeared,
0:38:45 > 0:38:49something on the sun changed that cooled the Earth down.
0:38:49 > 0:38:52But it wasn't that the solar output changed.
0:38:52 > 0:38:54No matter how many sun spots there are,
0:38:54 > 0:38:57the sun doesn't get any hotter or brighter.
0:39:04 > 0:39:07So the spots must have another effect.
0:39:07 > 0:39:10And to see it, we need a different way to look at the sun.
0:39:18 > 0:39:22It's not just heat and light that the sun is throwing at the Earth.
0:39:22 > 0:39:27As every sunbather knows, there's ultraviolet light too.
0:39:29 > 0:39:32Enough UV reaches the surface to burn our skin,
0:39:32 > 0:39:36but it is only a fraction of the sun's UV output.
0:39:38 > 0:39:42The rest is filtered out by the atmosphere.
0:39:43 > 0:39:47It means we don't get a complete picture of the sun from the Earth.
0:39:47 > 0:39:53To see it in all its glory, you have to go into space.
0:40:09 > 0:40:12From here, you can really see the changing sun.
0:40:20 > 0:40:25In the extreme UV, the sun spots burn a brilliant white.
0:40:34 > 0:40:38In the X-ray frequencies they look even more dramatic.
0:40:38 > 0:40:42Huge plumes of superheated gas spout from the spots.
0:40:48 > 0:40:51When you're seeing the visible, you're seeing the surface of the sun.
0:40:51 > 0:40:54When you see the ultraviolet with X-rays,
0:40:54 > 0:40:57you're seeing that hot atmosphere - a million degrees.
0:40:57 > 0:40:59The surface is about 6,000 degrees.
0:40:59 > 0:41:02So you're seeing a different part of the sun
0:41:02 > 0:41:05and you're seeing a part that's constantly changing.
0:41:08 > 0:41:12These phenomenal displays of solar power
0:41:12 > 0:41:16were only discovered in the 1970s by the astronauts on Skylab.
0:41:25 > 0:41:28No-one had seen the sun like this before.
0:41:34 > 0:41:38Since then, a number of space telescopes have been deployed,
0:41:38 > 0:41:41whose sole purpose is to look at the sun.
0:41:43 > 0:41:45The most used is SOHO -
0:41:45 > 0:41:49the Solar and Heliospheric Observatory.
0:41:51 > 0:41:56It sits a million miles away from the Earth, at the Lagrangian point,
0:41:56 > 0:42:00where the gravitational pull from the Earth and the sun is equal.
0:42:00 > 0:42:05Fixed in space, it has an uninterrupted view of the sun and its tantrums.
0:42:08 > 0:42:11It has completely transformed our understanding.
0:42:11 > 0:42:13You can essentially see right from
0:42:13 > 0:42:17inside the sun, right through to the coronal mass ejections
0:42:17 > 0:42:20as they're leaving the sun, so you're seeing out to 30 solar radii.
0:42:22 > 0:42:28SOHO has played a key role in understanding the explosive power of the sun.
0:42:29 > 0:42:32By blocking out the disc, it simulates an eclipse,
0:42:32 > 0:42:35revealing the outer atmosphere
0:42:35 > 0:42:39and the true scale of the sun's largest eruptions.
0:42:41 > 0:42:44These are solar flares and coronal mass ejections
0:42:44 > 0:42:48and they erupt from the heart of sun spots.
0:42:53 > 0:42:57The temperatures in a solar flare will be tens of millions of degrees,
0:42:57 > 0:43:03so it's an extremely hot, very dramatic change in temperature over a short period of time.
0:43:03 > 0:43:06When they erupt completely,
0:43:06 > 0:43:10you can get masses which are roughly the mass of Mount Everest
0:43:10 > 0:43:12being flung out into the solar system.
0:43:14 > 0:43:18At solar minimum, flares are infrequent.
0:43:18 > 0:43:22But every 11 years, when the cycle peaks at solar max,
0:43:22 > 0:43:28the sun puts on the best firework display in the solar system.
0:43:45 > 0:43:51Solar astronomers are now beginning to understand the cause of these explosions.
0:43:53 > 0:43:56They are not caused by the power of fusion.
0:43:56 > 0:43:59There is another force at work.
0:43:59 > 0:44:01It is the force of magnetism.
0:44:03 > 0:44:07The sun is covered in a complex network of magnetic fields.
0:44:07 > 0:44:12A magnetic map shows a familiar patchwork on the face of the sun.
0:44:14 > 0:44:20The areas of the strongest fields coincide exactly with the position of sun spots.
0:44:22 > 0:44:27Here, the magnetic field strength can be amplified 10,000 times
0:44:29 > 0:44:32The regions that have the strongest magnetic field
0:44:32 > 0:44:35on the sun are in the sun spots.
0:44:35 > 0:44:37And in the units that we use,
0:44:37 > 0:44:42sun spot magnetic fields are roughly 1,000, 2,000, maybe 3,000 gauss.
0:44:42 > 0:44:45But if you look at magnets like the ones I'm playing with here,
0:44:45 > 0:44:49the magnetic field of these is about 1,000 - 1,500 gauss,
0:44:49 > 0:44:54so these have the same magnetic field strength as a sun spot.
0:44:54 > 0:44:57The key difference is that a sun spot is an awful lot bigger,
0:44:57 > 0:45:03so the total energy - the amount of energy in the magnetic field on the sun - is enormous.
0:45:03 > 0:45:05But the field strength in any given location
0:45:05 > 0:45:07is something you can hold in your hand.
0:45:09 > 0:45:14Sun spots are just the visible effect of magnetic fields so strong
0:45:14 > 0:45:18that they can prevent heat and light rising from the sun's interior.
0:45:24 > 0:45:27With the right viewing equipment,
0:45:27 > 0:45:30you can even see the magnetic fields.
0:45:30 > 0:45:33Magnetic loops arch off the surface,
0:45:33 > 0:45:36like iron filings around a bar magnet,
0:45:36 > 0:45:40their shapes are mapped out by plasma heated to a million degrees.
0:45:40 > 0:45:45The largest are 200,000 kilometres high.
0:45:45 > 0:45:48And they are packed full of unstable energy.
0:45:48 > 0:45:52When you add up the total energy content in these loops,
0:45:52 > 0:45:56it comes out to roughly 10 to the 21 joules of energy.
0:45:56 > 0:46:01That's roughly ten times the annual energy consumption of the United States.
0:46:01 > 0:46:05Of course, we can see thousands of them at any one time.
0:46:10 > 0:46:15The loops are caused by the twisting of the sun's basic magnetic field.
0:46:18 > 0:46:23Because the sun rotates faster at the equator than at the poles,
0:46:23 > 0:46:25it drags the field lines with it,
0:46:25 > 0:46:28stretching and twisting them like elastic bands.
0:46:30 > 0:46:32As the solar cycle goes on,
0:46:32 > 0:46:34the fields get more and more twisted
0:46:34 > 0:46:36and break through the surface.
0:46:38 > 0:46:40Until, at solar max,
0:46:40 > 0:46:44the whole sun is covered in loops stretched to breaking point.
0:46:47 > 0:46:51Solar flares are what happen when the strain gets too much
0:46:51 > 0:46:53and the loops snap.
0:46:56 > 0:47:00Basically, all that energy comes out of the catastrophic release
0:47:00 > 0:47:03of energy that's been stored in the magnetic field.
0:47:03 > 0:47:06So, like if you wind up an elastic band too much
0:47:06 > 0:47:10and let it go with your fingers, that band flies across the room.
0:47:23 > 0:47:27When the energy bound within sun spots is released,
0:47:27 > 0:47:31billions of tonnes of plasma are fired far into space at huge speeds.
0:47:33 > 0:47:38And sometimes they are aimed straight for the Earth.
0:47:41 > 0:47:45The flares fly through space for two days.
0:47:48 > 0:47:50When they reach us,
0:47:50 > 0:47:54the Earth's own magnetic field deflects most of the blow.
0:47:54 > 0:48:00But it's the impact on the magnetic field which affects on Earth.
0:48:00 > 0:48:02It's called space weather
0:48:02 > 0:48:06and the best of its effects are magical.
0:48:08 > 0:48:12The auroras, dancing displays of celestial light,
0:48:12 > 0:48:15are caused by particles from the solar storm
0:48:15 > 0:48:18smashing through the magnetic field at the poles.
0:48:21 > 0:48:24When they strike the upper atmosphere,
0:48:24 > 0:48:26they light up the polar skies.
0:48:33 > 0:48:37In the strongest storms, at the peak of the solar cycle,
0:48:37 > 0:48:41the northern lights can be seen as far south as Athens and Cuba.
0:48:45 > 0:48:50But the buffeting of the magnetic field has other unseen effects.
0:48:56 > 0:49:02Migratory animals that navigate using the magnetic field can lose their bearings.
0:49:03 > 0:49:06Racing pigeons don't come home.
0:49:11 > 0:49:16And whale strandings have been seen to increase with solar activity.
0:49:19 > 0:49:26But most worryingly for us is the effect that the disrupted magnetic field can have on electronics.
0:49:35 > 0:49:39The strongest storms can damage or destroy satellites
0:49:39 > 0:49:41with devastating effects.
0:49:44 > 0:49:48We're more sensitive to the sun than we probably realise
0:49:48 > 0:49:51because when the sun releases this magnetic energy,
0:49:51 > 0:49:54in the form of solar flares and coronal mass ejections,
0:49:54 > 0:49:56maybe you don't notice it at first,
0:49:56 > 0:49:59but a crackle on your cell phone, or your cell phone going out,
0:49:59 > 0:50:04may actually be caused by enhanced activity on the sun.
0:50:11 > 0:50:14Mobile telephones, television,
0:50:14 > 0:50:17aeroplane navigation, even weapons guidance systems,
0:50:17 > 0:50:21all rely on satellite communication
0:50:21 > 0:50:24and all can be disturbed by space weather.
0:50:25 > 0:50:29The more we are reliant on these systems,
0:50:29 > 0:50:32the more we will feel the effects of the sun's tantrums.
0:50:39 > 0:50:44But we still don't understand all of the effects of space weather.
0:50:46 > 0:50:50No-one can explain the effect on the climate
0:50:50 > 0:50:54or why the disappearance of sun spots should cause an ice age.
0:50:57 > 0:50:59It may not matter.
0:50:59 > 0:51:03The small effect that solar variation has on the climate
0:51:03 > 0:51:07has long since been drowned out by man-made global warming.
0:51:11 > 0:51:13As the world warms up,
0:51:13 > 0:51:17the sun may yet prove an unlikely source of cooling.
0:51:17 > 0:51:21The greenhouse effect could be stopped by harnessing its heat.
0:51:21 > 0:51:24DRUMS AND CHANTING
0:51:30 > 0:51:32The American Indians of the south-west deserts
0:51:32 > 0:51:38have understood the importance of living sustainably with their environment for hundreds of years.
0:51:41 > 0:51:45We have these natural disasters, like the big old fires,
0:51:45 > 0:51:50the volcanoes erupting, the big old earthquakes, the tsunami.
0:51:50 > 0:51:53That's the Earth telling us that it's getting pretty tired.
0:51:53 > 0:51:56It's warning us that we need to slow down.
0:52:07 > 0:52:15On the Mesas of Arizona, far beyond the reach of the electricity grid, lies Old Oraibi -
0:52:15 > 0:52:18the oldest occupied settlement in North America.
0:52:18 > 0:52:23For 1,000 years, the Hopi Indians have lived here in harmony with their environment.
0:52:28 > 0:52:34But that doesn't mean that they have to live without the conveniences of modern life.
0:52:34 > 0:52:38They have just realized that they are already getting all the power they need.
0:52:41 > 0:52:44Under the clear skies of the desert,
0:52:44 > 0:52:48a family can be supplied with electricity from a couple of solar panels.
0:52:50 > 0:52:53Being that we pray to the sun every day,
0:52:53 > 0:52:59it's got our heartfelt desires. He receives it every day.
0:52:59 > 0:53:04We thought the best source of energy should come from the sun.
0:53:08 > 0:53:10A few miles across the desert,
0:53:10 > 0:53:15the idea is finally catching on with the rest of American civilization.
0:53:15 > 0:53:18But, naturally, it's on a much bigger scale.
0:53:21 > 0:53:27These are Stirling dishes - the daddy of solar power systems
0:53:27 > 0:53:33and they may be about to solve the energy crisis facing the cities of the American west.
0:53:35 > 0:53:38People want to run their air conditioners, their computers,
0:53:38 > 0:53:42their lights during the day and we run out of energy.
0:53:44 > 0:53:49We have a solar furnace 90 million miles away that provides life for all of Earth.
0:53:49 > 0:53:53In the past, we have been unable to harness that potential
0:53:53 > 0:53:57because the efficiency, the cost of the systems, didn't make it viable.
0:53:57 > 0:53:59What's changed is technology.
0:53:59 > 0:54:07The technology now allows us to build large-scale, highly efficient, cost effective systems.
0:54:08 > 0:54:11Each dish tracks the movement of the sun across the sky,
0:54:11 > 0:54:17focusing the heat onto a single point, where it is converted to electricity.
0:54:21 > 0:54:25They are twice as efficient as any other solar power system.
0:54:25 > 0:54:29With one, you could power a small village.
0:54:29 > 0:54:31A field of them could power a city.
0:54:34 > 0:54:39Each system produces about 25 kilowatts, which is enough to power about ten homes.
0:54:39 > 0:54:42However, we plan to deploy these on a large scale -
0:54:42 > 0:54:4920,000 of these, which is massive - the equivalent or a coal-fired plant or maybe even a nuclear plant.
0:54:51 > 0:54:57The ink is just drying on the contract to build the first commercial solar power station.
0:54:58 > 0:55:03It will fill five square miles of the vast Californian desert with mirrors
0:55:03 > 0:55:07and will supply electricity to the city of San Diego.
0:55:07 > 0:55:11In time, as the technology and efficiency improves,
0:55:11 > 0:55:15systems like these may spread around the world.
0:55:20 > 0:55:27These dishes are direct descendents of the stone monuments of Stonehenge and Orkney.
0:55:30 > 0:55:33Separated by 5,000 years,
0:55:33 > 0:55:37they all embody our desire to understand the sun,
0:55:37 > 0:55:41to be bathed in its light and to tap into its awesome power.
0:55:43 > 0:55:49He's quiet, he's clean, he's powerful.
0:55:49 > 0:55:52This is the way I was raised - I was raised to respect him
0:55:52 > 0:55:59and to offer those prayers to him for keeping us for the length of time that he has.
0:55:59 > 0:56:02He's done this for generations and generations,
0:56:02 > 0:56:05and hopefully he will, you know, in the future.
0:56:09 > 0:56:15The sun will probably shine down on our civilisations for as long as they exist.
0:56:15 > 0:56:20If we survive for another billion years, the sun will still be there.
0:56:24 > 0:56:29But, just as the sun was once born, it will one day die.
0:56:29 > 0:56:33And when it does so, it will take the Earth with it.
0:56:36 > 0:56:41In about five billion years' time, the sun will run out of hydrogen.
0:56:44 > 0:56:48When it does, it will become a red giant.
0:56:50 > 0:56:53Deprived of fuel, the core will shrink,
0:56:53 > 0:56:58generating so much heat that the outer layers will balloon into the solar system.
0:56:58 > 0:57:01The inner planets will be swept up.
0:57:04 > 0:57:07It may even swallow the Earth.
0:57:08 > 0:57:12Whether it is engulfed or not, the Earth is doomed.
0:57:14 > 0:57:19The sun, burning 2,000 times hotter than it does now,
0:57:19 > 0:57:22will melt and seal the outer layers of the planet.
0:57:26 > 0:57:30Then, suddenly, the sun will stop burning.
0:57:34 > 0:57:38As the remains of the solar system is plunged into darkness,
0:57:38 > 0:57:40the sun's core will collapse
0:57:40 > 0:57:46and, with its last gasp, it will blow its remaining shroud of gas into space.
0:57:48 > 0:57:51It will be forever night.
0:57:51 > 0:57:55The story of the sun and the Earth will have ended
0:57:55 > 0:58:01and a small part of the outer arm of the Milky Way will be a little bit darker.
0:58:03 > 0:58:06But around it, in the rest of the universe,
0:58:06 > 0:58:08the same story will be being told
0:58:08 > 0:58:12by a billion other small, insignificant stars
0:58:12 > 0:58:16twinkling in the vastness of space.
0:58:43 > 0:58:46Subtitles by Red Bee Media Ltd 2006
0:58:46 > 0:58:49E-mail subtitling@bbc.co.uk