"We live on a world of wonders." "A place of astonishing beauty and complexity." "We have vast oceans and incredible weather." "Giant mountains and breathtaking landscapes." "If you think that this is all there is, that our planet exists in magnificent isolation, then you're wrong." "As a physicist, I'm fascinated by how the laws of nature that shaped all this also shaped the worlds beyond our home planet." "I think we're living through the greatest age of discovery our civilisation has known." "We've voyaged to the farthest reaches of the solar system." "We've photographed strange new worlds, stood in unfamiliar landscapes, tasted alien air." "And at the heart of it all is the powerhouse." "A vast wonder that we greet each day." "A star that controls each and every world in its thrall." "Look at that!" "'The sun.'" "And when it goes, it really will be the end of us all." "This is Varanasi." "For Hindus, it's one of the holiest sites in all of India." "Part of what makes it so special is the orientation of its sacred river as it flows past the city." "This is the one place on the Ganges where you can bathe in the river on this shore and you can see the sunrise on the eastern shore." "It's the only place where the Ganges turns around to the north so you can do that." "When the sun rises tomorrow, a truly extraordinary phenomenon will take place:" "a total eclipse of the sun." "It's an auspicious occasion for a place that ancient Hindus knew as the Solar City." "Science is different to all the other systems of thought, the belief systems that have been practised in this city for millennia, because you don't need faith in it." "You can check that it works." "So, for example, I can tell you that tomorrow morning at precisely 6:24am the moon will cover the face of the sun and there will be a total solar eclipse." "I can tell you that in 2904 there will be five solar eclipses on the earth and I can tell you that on July 16th, 2186 there will be the longest solar eclipse for 5,000 - seven minutes." "The sun reigns over a vast empire of worlds, all moving like clockwork." "Everything within its realm obeys the laws of celestial mechanics defined by Sir Isaac Newton in the 17th century." "These laws allow us to predict exactly where each world will be for centuries to come." "And wherever you happen to be, if there's a moon between you and the sun, there will be an eclipse." "Of course, Jupiter, plenty of moons, and this is a rare picture taken by the Hubble space telescope in spring 2004 where you can see the shadows of three moons on the surface, three eclipses simultaneously." "Now, this kind of event only happens once every few decades." "Saturn, plenty of moons." "I think these are my favourite of all the pictures of eclipses in the solar system because these are pictures taken from the surface of Mars by the Opportunity rover looking up at the sun." "And you can see Mars's moon, Phobos, as it makes its way across the disk of the sun." "So this is a solar eclipse, partial solar eclipse, from the surface of another world." "The astronomers of the future will discover that these partial eclipses can never measure up to the ones back home." "And that's because, here on Earth, humans have the best seat in the solar system from which to enjoy the spectacle of a total eclipse of the sun." "All thanks to a wonderful quirk of fate." "The sun is 400 times the diameter of the moon but, by sheer coincidence, it's 400 times further away from the earth." "So when our moon passes in front of the sun, then it can completely obscure it." "Now there's something like between, what, 145 and 167 moons in the solar system, depending on how you count them, but none of them produce such perfect eclipses as the earth's moon." "This accidental arrangement of the solar system means we're living in exactly the right place and, tomorrow morning, exactly the right time to enjoy the most precious of astronomical events." "Our closest star is the strangest, most alien world in the solar system." "It's a place we can never hope to visit but I want to show you that, through space exploration and a few chance discoveries, our generation is getting to know the sun in exquisite new detail." "For us, it's everything and yet it's just one ordinary star amongst 200 billion starry wonders that make up our galaxy." "This is the remote frontier of the solar system, a dwarf planet known as Sedna." "Seen from out here, 13 billion kilometres away from Earth, the sun is just another star." "Uranus is 10 billion kilometres closer in, but even so, sunrise is barely perceptible." "The sun hangs in the sky 300 times smaller than it appears on Earth." "Further in, we come to Saturn." "Its spectacular rings reflect the sun's light onto its dark side." "This planet is bathed, not just in sunshine, but in ring-shine." "230 million kilometres out, we arrive at the first world with a more familiar view of the sun." "This is sunset on Mars, as seen by the robotic rover, Spirit." "Past Earth, 150 million kilometres out, we continue to head to the heart of the solar system." "Mercury is the closest planet, just 46 million kilometres out." "It spins so slowly that sunrise to sunrise lasts for 176 Earth days." "Beyond, there is nothing but the naked sun, a colossal fiery sphere of tortured matter, burning with a temperature at its core of over 15 million degrees Celsius." "Throughout human history, this majestic wonder has been a constant source of comfort, awe and worship." "This is Death Valley in California, regularly the hottest place on the planet, and today the car says it's 111 degrees Fahrenheit," "45 degrees Celsius." "For centuries, the finest minds in science struggled to understand the origin of the sun's seemingly endless heat and energy." "What is it made of?" "Where did it come from?" "And what is the source of its phenomenal power?" "Then, in 1838, British physicist John Herschel, took on the endeavour in his experimental attempt to catch a sunbeam." "So how much energy does fall on the surface of the earth from the sun?" "You can work it out with a beautifully simple experiment using only a thermometer, a tin full of water and an umbrella." "Basically, you let the water heat up in the tin to ambient temperature which, here in Death Valley today, is about 46 degrees Celsius." "And then you put the thermometer in the water and you take the shade away and let the sun shine on the water." "In direct sunlight, the water temperature begins to rise." "By timing how long it takes the sun to raise the water temperature by one degree Celsius, you can figure out exactly how much energy the sun has delivered into the can of water, and from that, how much energy is delivered" "to a square metre of the surface." "It turns out that, on a clear day when the sun is vertically overhead, that number is about a kilowatt." "That's ten 100 watt bulbs can be powered by the sun's energy for every metre squared of the earth's surface." "In an audacious leap of imagination, Herschel used this figure to calculate the entire energy given off by the sun." "So imagine adding up those kilowatts over this entire landscape." "And then imagine following the sun's rays as they cover the entire surface of the earth." "But then, imagine this, the earth is 150 million kilometres away from the sun, so actually, the sun is radiating energy out across a giant sphere with a radius of 150 million kilometres surrounding our star." "How much energy does that make?" "It's four x pi x the distance to the sun squared, which is about..." "It's 400 million million million million watts." "That is a million times the power consumption of the United States every year, radiated in one second." "And we worked that out by using some water, a thermometer, a tin and an umbrella." "And that's why I love physics." "It's a wonder of our star that it's managed to keep up this phenomenal rate of energy production for millennia." "Stars like the sun are incredibly long-lived and stable." "Our best estimate for the age of the universe is 13.73 billion years and the sun has been around for five billion years of that." "That's more than a third the age of the universe itself." "So what possible power source could allow the sun to shine with such intensity day after day for five billion years?" "The best way to find the answer is to go back to the very beginning." "And it all began from, well, pretty much nothing." "There was a time when this corner of the galaxy was without light." "The sun had yet to begin." "The story of how our star was born can be read in the night sky." "If you take a picture of the Milky Way, then one of the first things you notice are these dark lines, these dark clouds running through it, an absence of stars and, in fact, those dark areas are called molecular clouds." "They're clouds of molecular hydrogen and dust that are lying in between us and the stars of the Milky Way galaxy." "These dark clouds contain the raw material from which stars are made - vast stellar nurseries that are amongst the coldest and most isolated places in the galaxy." "In the centre of some of those clouds, the temperature is as low as ten degrees above absolute zero." "Now, that matters because temperature is a measure of how fast things are moving." "So, in these clouds, the clumps of hydrogen and dust are moving very slowly." "Only in this extreme cold can gravity grab hold of the clouds' constituent particles." "Over millennia, they begin to condense." "That means that the weak force of gravity can take over and begin to clump the hydrogen together." "Now, we have a name for clumps of hydrogen collapsing under their own gravity - stars." "So, as those clouds of hydrogen collapse further and further under the force of gravity, they begin to heat up and eventually, in their cores, they become hot enough for the hydrogen to begin to fuse together into helium." "The stars ignite, the clouds are no longer black and the lifecycle of a new star has begun." "This very story played out five billion years ago when a star was born that would come to be known as the sun." "And its birth reveals the secret of our star's extraordinary resources of energy, because the sun, like every other star, was set alight by the most powerful known force in the universe." "The fusion of hydrogen into helium is the foundation of all the sun's power." "Boundless energy that reaches out and connects this wonder to all of the worlds in its realm." "This is the Iguazu River which flows into the Parana, one of the great rivers of the world, and it's these river systems that drain all the rainfall from the southern Amazonian basin eventually into the Atlantic." "Just look how much water there is." "Every molecule in this river, every molecule in every raindrop in every cloud, has been transported from the Pacific over the Andes and into the continental interior here." "Just imagine how much energy that needs." "And all that energy - every bit of it, comes from the sun." "The sun is the power that lifts all the water on the blue planet." "And in places, it comes down again to create some of the most breath-taking sights on Earth." "This is Iguazu Falls." "A quarter of a million gallons of water flow through here every second." "The spectacular energy of the falls is a wonderful example of how this planet is hard-wired to the constant and unfailing power of the sun." "The energy we see from the sun may seem utterly constant, but tiny fluctuations in its brightness can be seen with a digital camera and the right know-how." "Now, it's not too difficult to take a picture of the sun even though it's 93 million miles away because it's big." "Of course, you've got to be careful." "We've got a filter on here that takes out pretty much all of the light because focusing the light from a nuclear reactor onto your camera or your retina wouldn't be a great idea, so you've got to be careful." "I'll take a picture." "Well, this is our picture of the sun that we took on June 20th, 2009." "You can see it's a beautiful... ..orb, with not a mark on the surface." "I suppose that's pretty much what most people would expect." "It's certainly what Aristotle and the ancient astronomers expected because they thought the heavens were perfect and unchanging." "But, look at this picture taken on March 29th, 2001." "You see a completely different story." "The surface of the sun is covered in black spots - sun spots." "Some of these vast structures are large enough to engulf the entire Earth." "Space observation has allowed us to track their numbers as they ebb and flow across the face of the sun." "The greater the number of sunspots, the more powerful our star becomes, threatening everything from astronauts to the electricity grids back on Earth." "We've discovered that the sun has seasons." "For decades, scientists have sought to understand how these subtle changes in the sun's power might be affecting the earth." "It's a puzzle that led one man to look away from the sun and focus instead on the rivers around the Iguazu Falls." "Argentinean astrophysicist, Pablo Mauas." "It's a very large river." "It's the fourth river in the world." "Unlike other larger rivers than the Parana, for example, the Amazon or Congo, we have data of this river for the whole 20th century." "So you can look back to what, about 1900 or...?" "Yes, from 1900, 1904." "And this is because this is a river that can be navigated by very large ships." "Pablo brought the statistical tools of a physicist to bear on 100 years worth of precious river records." "What emerged was that the river, too, had a rhythm." "We found that the stream flow of the river goes up and down and up again and down again three times during the century." "And then we went further, trying to understand why." "The amount of water in the Parana River seems to be following a pattern." "The question is, what could be driving the change in these vast river systems?" "Pablo first looked to the 11-year sunspot cycle, but found no fit." "So instead, he turned to calculations that described the sun's underlying brightness during the last century." "He showed me what happened when you superimpose this solar data on the water levels in the river." "You see that when the sun goes up, the river goes up." "So what this is saying is, around 1925 or so, there was more solar activity, so the amount of, really, the solar radiation falling on the earth." "Right, there was relatively more activity, solar activity, in these three periods we can see here." "I mean, it's a beautiful correlation between the water flow, the flow in these rivers and the solar output." "Yes, it is." "We find it's a very striking correlation." "Changes in the sun seem to move weather systems elsewhere, too." "In India, the monsoon appears to follow a similar pattern to the Parana river, whereas in the Sahara, the opposite seems to occur." "More solar activity, less rain." "The exact mechanisms by which our star may affect Earth's weather remain, for now, a mystery." "We know that the energy production rate of the sun, the power released in the fusion reactions at the core, is very constant indeed." "It doesn't change as far as we can tell, and so the changes that we see must be to do with the way the energy gets out of the sun." "And, whilst it's only at the tenths of a percent level in the amount of radiation that falls onto the surface of the earth, it really does reveal the intimacy and delicacy of the connection between the sun and the earth." "And this connection is the secret to another of the sun's wonders." "Of all the stars in the universe, we know of only one where a phenomenon has arisen which feeds on starlight." "These leaves are wonderful machines, nature's way of harnessing the power of the sun." "But they're fussy eaters." "They've evolved to use just a fraction of the sunlight that makes its way through Earth's atmosphere." "Here on the surface, sunlight may appear white." "But when you pass it through a prism, you see it's made up of all the colours of the rainbow." "The prism splits sunlight into its component colours, revealing the red, green and blue photons." "And it's not just their colour that distinguishes them." "The red photons don't carry much energy, there are lots of them, whereas the blue photons, although there are fewer, carry a lot of energy." "And plants use the red bit of the spectrum, and they use the blue bit of the spectrum, but they don't use as much of the green." "That's reflected and so that's why, when you look around a forest like this on a sunny day, you just see a sea of green." "So the wonderful colour of the forest is all down to how plants have adapted to the quality of our star's light." "And it's this ability to harvest sunlight which lies at the base of the complex food chain which nourishes, well, pretty much all life on Earth." "Each and every one of us is sustained by the sun's light, an umbilical cord of sunshine that stretches across 150 million kilometres of space." "But beyond the visible power of the sun lies another realm." "These are the unseen forces by which it maintains influence over its domain." "And, very occasionally, the solar system arranges itself so that we can glimpse this invisible kingdom with our own eyes." "It's 5.28, so that's time of first contact and you can't see the disc of the sun at the moment, it's obscured by low cloud." "The edge of the moon is, at this point, just beginning to touch the disc of the sun." "You can see the sun emerging through the clouds, see the disc." "Oh, and you can see the moon." "Can you see the moon on the top?" "Oh, yeah!" "It just vanished." "Can you see the rim of the moon there?" "Absolutely fantastic." "Yeah?" "See the sun?" "CROWD CHATTERS" "You can see the celestial mechanics, the clockwork of the solar system at work." "The alignment is absolutely perfect." "CHATTERING STOPS" "Look at that!" "If you EVER needed convincing that we live in a solar system, that we are on a ball of rock orbiting around the sun with other balls of rock, then look at that." "That's the solar system coming down and grabbing you by the throat." "'The sun's face is now completely shrouded by the moon." "'Only now, during totality, is the hidden wonder of the sun revealed.'" "Look, I mean, that's the sun's atmosphere, that's not clouds." "There are no clouds there now." "That's the solar corona." "That's the atmosphere of our star shining out." "The sun's atmosphere is strange." "It's made up of a thin collection of charged particles, protons and electrons." "Through mechanisms that we don't yet fully understand, the corona is much hotter than the surface." "Here, temperatures soar to over a million degrees Celsius, some 200 times hotter than the visible surface." "Each and every day, right at the very top of the atmosphere, some of the most energetic coronal particles are escaping." "The sun leaks nearly seven billion tons of corona every hour into space, a vast, superheated, supersonic collection of smashed atoms that en masse are known as the solar wind." "This is the beginning of an epic journey that will see the sun's breath reach out to the furthest parts of the solar system." "Look at that!" "CHEERING AND APPLAUSE" "'All too soon, this brief glimpse of the solar wind's origin is gone.'" "It's the most incredible thing I've ever seen, actually." "Amazing when, when the sun re-emerged from behind the moon." "Everybody just..." "like that..." "Goes..." "Wow!" "The solar wind may be invisible to us, but each day, tiny pieces of our star are constantly blowing our way." "Now, by the time the solar wind reaches the Earth, it's pretty dilute." "You know if you were to go out into space close to the Earth and hold your hand up there, you wouldn't feel anything." "In fact there are about five protons and five electrons for every sugar cube's worth bit of space, but still they're travelling very fast and they carry a lot of energy, enough energy in fact over time to blow the earth's atmosphere off into space." "So how does life on our planet survive this lethal gale?" "'To find the answer, I need to head north." "'On a beautiful sunny winter's day in the Arctic, it's hard to imagine that our star could be a threat." "'But high above us, deadly solar particles are streaming 'our way at speeds topping a million kilometres an hour.'" "Down here on the Earth's surface, we're protected from that intense solar wind that's battering our planet because the Earth has a natural shield that deflects most of the solar wind around it." "And to see that shield, you just need a simple shield detector which is a compass." "And that's because the earth's force field is magnetic, an invisible shell that surrounds the planet in a protective cocoon." "It's very similar to the shape of the field around the bar magnets and you can see that shape by moving a compass around it." "The compass needle follows the magnetic field lines, and the Earth field is actually very similar in shape to this one." "The magnetic field emanates from deep within our planet's spinning iron-rich core." "And it's this gigantic force field, known as the magnetosphere, that deflects most of the lethal solar wind harmlessly away into space." "But the planet doesn't escape completely." "When the solar wind hits the Earth's magnetic field, it distorts it." "It stretches the field out on the night side of the planet and in some ways it's like stretching a piece of elastic." "More and more energy goes into the field." "Over time, this energy builds up stretching the tail, until it can no longer hold onto it all." "Eventually, the energy is released, accelerating a stream of electrically charged particles down the field lines towards the poles." "And when these particles that have been energised by the solar wind hit the Earth's atmosphere, they create one of the most beautiful sights in nature - the aurora borealis, or Northern Lights." "'I've come to the far north of Norway 'in hope of seeing the solar wind's influence on our planet for myself, 'to see the mystical aurora for the first time.'" "Seeing the aurora on any given night is far from certain." "'So to shorten the odds, I've recruited the help of an astrophysicist," "'Professor Mike Lockwood.'" "So Mike, not that I'm complaining, but other than for reasons of pure enjoyment, why did we have to come to the Arctic Circle on snowmobiles?" "The city street lights produce a light pollution that actually make it hard to see the aurora and it's good we've come at the end of winter because the energy we take out the solar wind is stronger." "Yes, so this is, I suppose then, the perfect day because we're in late March, completely blue sky." "Fabulous." "If this stays, we've got 80% chance tonight." "Soon after dusk, and despite clear skies, there's no early performance from the aurora." "So while we wait, Mike runs a film loop of the Northern Lights as seen from an extraterrestrial perspective." "So that's a beautiful image." "I haven't seen an image like that before." "It was taken from above the pole?" "Yeah, that's a spacecraft in orbit around the planet, yes, going from pole to pole." "'From space, you can really see the impact of the solar wind." "'Its energy feeds an unbroken circuit of aurora that surrounds the pole.'" "And we will feel that it's a display put on just for us here." "When you see the pictures from space, you realise everybody on that oval is getting the display." "Well, my hope is that we'll be directly underneath that tiny thin band tonight here in Tromso." "Thankfully, our luck holds and the skies remain crystal clear, until at last, energy brought by the solar wind sets the upper atmosphere alight." "Absolutely amazing sight." "Arcs, but more like curtains of green." "It doesn't look to me like it's cascading down." "It looks like it's rising up from the ground." "It is quite incredibly beautiful, and I thought before I'd seen it that I would think it was all the more wonderful because I knew that I was seeing a visual manifestation of the earth's magnetic field protecting us from the solar wind," "but I don't think that." "Actually over there, there's a green shaft of light that looks like it's rising up out of the mountain in the distance and it looks like spirits drifting up from the mountain into heaven." "Absolutely magnificent." "Our environment doesn't stop at the edge of our atmosphere." "In fact our environment stretches at least as far as the sun which is an obvious statement to make in the daytime because you can feel the heat of the sun, but in the night time, you see this other side." "You see this unseen and constant solar wind." "Beyond earth, the solar wind continues to race out into the solar system and wherever it encounters a planet with a magnetosphere, aurora spring up." "Jupiter's magnetic field is the largest and most powerful in the solar system." "Seen from the Hubble space telescope, the aurora here are a permanent fixture over the Jovian poles." "Saturn, too, puts on an impressive display as seen in this remarkable footage." "Eventually, though, way beyond the planets, the solar wind begins to run out of steam." "It's travelled non-stop for 16 billion kilometres, over 100 times the distance of the Earth from the sun." "And incredibly, we have a probe out there which is about to discover exactly where the wind from the sun ends." "When I was about five, I collected these cards, the Race Into Space." "It starts with Sputnik and it's a history of space, and right at the end there's the speculative stuff about moon base and then a manned mission to Mars, on November 12th 1981, it was going to leave." "In there is the Grand Tour proposal by NASA to go to Jupiter, Saturn, Uranus, Neptune and it actually went." "I remember in '77 being excited and watching the launch and thinking this is, my card has come to pass, it's come to be." "And astonishingly, I think, we're still in contact with this thing now." "A pair of spacecraft were sent out on the Grand Tour, Voyagers one and two." "Both are alive and well, and Voyager one reports back to earth here." "Now, also in my book was this picture, the Goldstone Mars station in the Mojave desert." "And there it is, 210 feet or it was at the time this book was written." "It's been expanded since and it's one of the few telescopes in the world that's capable of communicating with Voyager which is ten billion miles from the Earth." "Today, the Goldstone station is listening out for the faintest whisper from Voyager one." "Call 233, oh, it's almost there now, so we should be seeing it coming in." "'Voyager is so far away that it takes the signal 'around 15 hours to arrive, travelling at the speed of light.'" "Oh, that triangle?" "Yeah, that's it, right there." "There." "'It may appear as little more than a blip on a screen but for me, it's beautiful.'" "I mean, you just have to think about it, this little thing, it's no bigger than a double-decker bus, designed in the late '60s, launched in the mid-'70s and still functioning 32 years later," "and good science data is still coming out of that little space craft." "I think it's absolutely wonderful." "Both Voyager spacecraft are constantly measuring the solar wind as it fades away." "One day soon, they will find the place where the sun's last physical trace finally runs out." "They'll leave the star that raised them behind and head off into interstellar space." "But even at that place, ten billion miles away where the solar wind meets the interstellar wind, that isn't the end of the story." "That isn't the edge of the sun's influence." "'The sun has a final invisible force that reaches out much further." "'Our star is, by far, the largest wonder in the solar system." "'In fact, it alone is 99% of the solar system's mass." "'It's this immensity that gives the sun its furthest reaching influence... ..gravity." "So its gravitational field dominates and all the planets are bound gravitationally to it." "The Earth for example, 93 million miles away, also known as one astronomical unit so let's represent that by one centimetre..." "And the most distant planet, Neptune, 30 astronomical units so 30 centimetres." "We then meet the Kuiper belt objects of which Pluto, the ex-planet, is a member." "They inhabit a region around 50 astronomical units so that is the size of the solar system in terms of... well, all the planets and all the Kuiper belt objects out to Pluto, but it doesn't stop there." "'Beyond Pluto, space is a cocktail of extremely dilute gas and dust,' mostly just hydrogen and helium left over from the universe's beginning at the Big Bang." "But every now and then, you encounter lumps of ice in vast orbits that take millennia to loop around the sun." "And that cloud of snowballs is called the Oort cloud." "'And astonishingly, the sun's grip is so strong 'that objects in the Oort cloud keep popping up all the way to out here.'" "Now, that cloud of dirty snowballs, still gravitationally bound to the sun, extends out 50,000 astronomical units." "On our scale, that's half a kilometre from the sun and remember, the Earth was one centimetre away." "This, then, is the full extent of the sun's empire, the lightest gravitational touch which retains a cloud of ice, enclosing the sun in a colossal sphere." "Beyond the Oort cloud, there is nothing." "Only sunlight escapes, light that will take four years before it reaches even the sun's closest neighbour, Proxima Centauri, a red dwarf star among the 200 billion others that make up the Milky Way." "And it's by looking here, deep into our local galactic neighbourhood, that we're learning to read the story of our own star's ultimate fate." "The sun's empire is so vast and so ancient and its power so immense, it seems like an audacious thought to think that we could even begin to comprehend its end - the death of our sun." "But that's what astronomers are trying to do and many of them come here to the most arid and barren desert on earth, the Atacama in Chile, and that's because the skies here are some of the clearest on earth." "'It's the end of my journey through the empire of the sun.'" "I've come to Paranal, high up on an extinct volcano." "It's home to the world's most powerful array of telescopes." "I've got to tell you this." "This is great." "You get important information you should know for a safe stay on Paranal because it's about 2,500 metres, two and a half kilometres in the air, and it says here that if during your stay you experience any of the following, consult a paramedic immediately..." "So there's headache and dizziness, breathing problems, ringing or blocking of the ears..." "SEEING STARS." "It honestly says 'If you see stars at the Paranal Observatory, consult a paramedic immediately!" "'" "'Perched high above the clouds, four colossal instruments 'make up the European Southern Observatory's Very Large Telescope, or VLT.'" "Even with the naked eye, the seeing here is spectacular." "The first thing you notice streaking across the sky is the Milky Way." "You can have no doubt when you look at that that we live in a galaxy of billions of stars." "The next thing you notice, if you look a little bit more carefully, is the stars are not just white points of light against the blackness of the sky." "They're actually coloured." "You see orangey-red stars, yellow stars and bluey-white stars." "Absolutely beautiful." "Astronomers have gazed upon the galaxy full of stars at all stages of their lives, from youthful, bright stars to middle-aged yellow stars very similar to the sun." "They've meticulously charted the nearest 10,000 of them, and then arranged each according to its colour and brightness." "What emerges is one of the most powerful and elegant tools in the whole of astronomy, the Hertzsprung-Russell diagram." "And so this diagram allows astronomers to predict the history and evolution of stars, and in particular, the future life of our sun." "There's real structure here." "There's this line that goes up from red stars through yellow stars to white stars, and this is called the main sequence." "The sun will spend most of its life in the main sequence, steadily burning its vast reserves of hydrogen fuel which will last for at least another five billion years." "But eventually the fuel will run out and its core will collapse." "'Then something remarkable will happen.'" "The sun's outer layers will expand and its colour will shift." "Mercury will be little more than a memory as it's engulfed by the expanding red sun." "It will grow to 200 times its size today, stretching all the way out to the Earth's orbit where our own planet's prospects are dim." "The wonder that has remained so constant throughout all of its ten billion years of life will end its days as a red giant star." "For a few brief instants, it will be 2,000 times as bright as it is now but that won't last for long." "Eventually it'll shed its outer layers and all that will be left will be its cooling core, a faint cinder that will glow, well, pretty much to the end of time." "And all its wonders, the aurora that danced through the atmospheres of planets of the solar system, and its light that sustains all the life here on earth, will be gone." "'But the gas and dust of the dying sun will drift off into space, 'in time to form a vast dark cloud primed and full of possibilities." "Until one day, another star will be born, perhaps, with a similar story to tell, the greatest story of the cosmos." "Subtitles by Red Bee Media Ltd" "E-mail subtitling@bbc.co.uk"