0:00:04 > 0:00:07We live on a world of wonders.
0:00:07 > 0:00:13A place of astonishing beauty and complexity.
0:00:14 > 0:00:16We have vast oceans
0:00:16 > 0:00:19and incredible weather.
0:00:19 > 0:00:24Giant mountains and breathtaking landscapes.
0:00:24 > 0:00:26If you think that this is all there is,
0:00:26 > 0:00:30that our planet exists in magnificent isolation,
0:00:30 > 0:00:31then you're wrong.
0:00:34 > 0:00:39As a physicist, I'm fascinated by how the laws of nature
0:00:39 > 0:00:44that shaped all this also shaped the worlds beyond our home planet.
0:00:47 > 0:00:51I think we're living through the greatest age of discovery
0:00:51 > 0:00:54our civilisation has known.
0:00:54 > 0:00:58We've voyaged to the farthest reaches of the solar system.
0:00:58 > 0:01:02We've photographed strange new worlds,
0:01:02 > 0:01:06stood in unfamiliar landscapes, tasted alien air.
0:01:10 > 0:01:13And at the heart of it all is the powerhouse.
0:01:15 > 0:01:18A vast wonder that we greet each day.
0:01:22 > 0:01:27A star that controls each and every world in its thrall.
0:01:29 > 0:01:30Look at that!
0:01:30 > 0:01:32'The sun.'
0:01:38 > 0:01:43And when it goes, it really will be the end of us all.
0:02:11 > 0:02:12This is Varanasi.
0:02:12 > 0:02:16For Hindus, it's one of the holiest sites in all of India.
0:02:19 > 0:02:21Part of what makes it so special
0:02:21 > 0:02:25is the orientation of its sacred river as it flows past the city.
0:02:25 > 0:02:29This is the one place on the Ganges where you can bathe in the river
0:02:29 > 0:02:33on this shore and you can see the sunrise on the eastern shore.
0:02:33 > 0:02:39It's the only place where the Ganges turns around to the north so you can do that.
0:02:39 > 0:02:41When the sun rises tomorrow,
0:02:41 > 0:02:45a truly extraordinary phenomenon will take place:
0:02:45 > 0:02:47a total eclipse of the sun.
0:02:47 > 0:02:49It's an auspicious occasion
0:02:49 > 0:02:54for a place that ancient Hindus knew as the Solar City.
0:02:56 > 0:03:00Science is different to all the other systems of thought,
0:03:00 > 0:03:02the belief systems that have been practised
0:03:02 > 0:03:06in this city for millennia, because you don't need faith in it.
0:03:06 > 0:03:08You can check that it works.
0:03:08 > 0:03:12So, for example, I can tell you that tomorrow morning at precisely 6:24am
0:03:12 > 0:03:14the moon will cover the face of the sun
0:03:14 > 0:03:16and there will be a total solar eclipse.
0:03:16 > 0:03:18I can tell you that in 2904
0:03:18 > 0:03:22there will be five solar eclipses on the earth
0:03:22 > 0:03:25and I can tell you that on July 16th, 2186
0:03:25 > 0:03:30there will be the longest solar eclipse for 5,000 - seven minutes.
0:03:41 > 0:03:47The sun reigns over a vast empire of worlds, all moving like clockwork.
0:03:52 > 0:03:57Everything within its realm obeys the laws of celestial mechanics
0:03:57 > 0:04:00defined by Sir Isaac Newton in the 17th century.
0:04:06 > 0:04:10These laws allow us to predict exactly where each world will be
0:04:10 > 0:04:12for centuries to come.
0:04:14 > 0:04:17And wherever you happen to be,
0:04:17 > 0:04:22if there's a moon between you and the sun, there will be an eclipse.
0:04:33 > 0:04:36Of course, Jupiter, plenty of moons, and this is a rare picture
0:04:36 > 0:04:40taken by the Hubble space telescope in spring 2004
0:04:40 > 0:04:43where you can see the shadows of three moons on the surface,
0:04:43 > 0:04:46three eclipses simultaneously.
0:04:46 > 0:04:50Now, this kind of event only happens once every few decades.
0:04:50 > 0:04:52Saturn, plenty of moons.
0:04:52 > 0:04:56I think these are my favourite of all the pictures of eclipses
0:04:56 > 0:04:57in the solar system
0:04:57 > 0:05:00because these are pictures taken from the surface of Mars
0:05:00 > 0:05:03by the Opportunity rover looking up at the sun.
0:05:03 > 0:05:06And you can see Mars's moon, Phobos,
0:05:06 > 0:05:09as it makes its way across the disk of the sun.
0:05:09 > 0:05:13So this is a solar eclipse, partial solar eclipse,
0:05:13 > 0:05:16from the surface of another world.
0:05:20 > 0:05:25The astronomers of the future will discover that these partial eclipses
0:05:25 > 0:05:29can never measure up to the ones back home.
0:05:33 > 0:05:36And that's because, here on Earth,
0:05:36 > 0:05:39humans have the best seat in the solar system
0:05:39 > 0:05:44from which to enjoy the spectacle of a total eclipse of the sun.
0:05:44 > 0:05:48All thanks to a wonderful quirk of fate.
0:05:48 > 0:05:52The sun is 400 times the diameter of the moon but,
0:05:52 > 0:05:57by sheer coincidence, it's 400 times further away from the earth.
0:05:57 > 0:06:00So when our moon passes in front of the sun,
0:06:00 > 0:06:04then it can completely obscure it.
0:06:04 > 0:06:07Now there's something like between, what,
0:06:07 > 0:06:10145 and 167 moons in the solar system,
0:06:10 > 0:06:12depending on how you count them,
0:06:12 > 0:06:17but none of them produce such perfect eclipses as the earth's moon.
0:06:23 > 0:06:26This accidental arrangement of the solar system
0:06:26 > 0:06:29means we're living in exactly the right place
0:06:29 > 0:06:33and, tomorrow morning, exactly the right time
0:06:33 > 0:06:36to enjoy the most precious of astronomical events.
0:06:41 > 0:06:44Our closest star is the strangest,
0:06:44 > 0:06:46most alien world in the solar system.
0:06:46 > 0:06:51It's a place we can never hope to visit but I want to show you that,
0:06:51 > 0:06:55through space exploration and a few chance discoveries,
0:06:55 > 0:07:00our generation is getting to know the sun in exquisite new detail.
0:07:03 > 0:07:08For us, it's everything and yet it's just one ordinary star
0:07:08 > 0:07:13amongst 200 billion starry wonders that make up our galaxy.
0:07:22 > 0:07:27This is the remote frontier of the solar system,
0:07:27 > 0:07:29a dwarf planet known as Sedna.
0:07:36 > 0:07:41Seen from out here, 13 billion kilometres away from Earth,
0:07:41 > 0:07:44the sun is just another star.
0:07:51 > 0:07:54Uranus is 10 billion kilometres closer in,
0:07:54 > 0:07:59but even so, sunrise is barely perceptible.
0:07:59 > 0:08:04The sun hangs in the sky 300 times smaller than it appears on Earth.
0:08:10 > 0:08:13Further in, we come to Saturn.
0:08:13 > 0:08:18Its spectacular rings reflect the sun's light onto its dark side.
0:08:18 > 0:08:23This planet is bathed, not just in sunshine, but in ring-shine.
0:08:28 > 0:08:30230 million kilometres out,
0:08:30 > 0:08:33we arrive at the first world
0:08:33 > 0:08:36with a more familiar view of the sun.
0:08:36 > 0:08:42This is sunset on Mars, as seen by the robotic rover, Spirit.
0:08:49 > 0:08:52Past Earth, 150 million kilometres out,
0:08:52 > 0:08:57we continue to head to the heart of the solar system.
0:09:02 > 0:09:07Mercury is the closest planet, just 46 million kilometres out.
0:09:07 > 0:09:15It spins so slowly that sunrise to sunrise lasts for 176 Earth days.
0:09:18 > 0:09:22Beyond, there is nothing but the naked sun,
0:09:24 > 0:09:27a colossal fiery sphere of tortured matter,
0:09:27 > 0:09:31burning with a temperature at its core
0:09:31 > 0:09:33of over 15 million degrees Celsius.
0:09:36 > 0:09:40Throughout human history, this majestic wonder
0:09:40 > 0:09:44has been a constant source of comfort, awe and worship.
0:09:56 > 0:09:58This is Death Valley in California,
0:09:58 > 0:10:00regularly the hottest place on the planet,
0:10:00 > 0:10:04and today the car says it's 111 degrees Fahrenheit,
0:10:04 > 0:10:0745 degrees Celsius.
0:10:08 > 0:10:14For centuries, the finest minds in science struggled to understand
0:10:14 > 0:10:18the origin of the sun's seemingly endless heat and energy.
0:10:18 > 0:10:20What is it made of?
0:10:20 > 0:10:21Where did it come from?
0:10:21 > 0:10:24And what is the source of its phenomenal power?
0:10:30 > 0:10:35Then, in 1838, British physicist John Herschel, took on the endeavour
0:10:35 > 0:10:40in his experimental attempt to catch a sunbeam.
0:10:41 > 0:10:45So how much energy does fall on the surface of the earth from the sun?
0:10:45 > 0:10:49You can work it out with a beautifully simple experiment
0:10:49 > 0:10:53using only a thermometer, a tin full of water and an umbrella.
0:10:53 > 0:10:56Basically, you let the water heat up in the tin to ambient temperature
0:10:56 > 0:11:02which, here in Death Valley today, is about 46 degrees Celsius.
0:11:02 > 0:11:07And then you put the thermometer in the water
0:11:07 > 0:11:09and you take the shade away
0:11:09 > 0:11:12and let the sun shine on the water.
0:11:13 > 0:11:18In direct sunlight, the water temperature begins to rise.
0:11:18 > 0:11:20By timing how long it takes the sun
0:11:20 > 0:11:23to raise the water temperature by one degree Celsius,
0:11:23 > 0:11:26you can figure out exactly how much energy
0:11:26 > 0:11:29the sun has delivered into the can of water,
0:11:29 > 0:11:32and from that, how much energy is delivered
0:11:32 > 0:11:34to a square metre of the surface.
0:11:34 > 0:11:38It turns out that, on a clear day when the sun is vertically overhead,
0:11:38 > 0:11:40that number is about a kilowatt.
0:11:40 > 0:11:44That's ten 100 watt bulbs can be powered by the sun's energy
0:11:44 > 0:11:47for every metre squared of the earth's surface.
0:11:52 > 0:11:57In an audacious leap of imagination, Herschel used this figure
0:11:57 > 0:12:01to calculate the entire energy given off by the sun.
0:12:04 > 0:12:09So imagine adding up those kilowatts over this entire landscape.
0:12:13 > 0:12:16And then imagine following the sun's rays
0:12:16 > 0:12:19as they cover the entire surface of the earth.
0:12:24 > 0:12:26But then, imagine this,
0:12:26 > 0:12:31the earth is 150 million kilometres away from the sun,
0:12:31 > 0:12:36so actually, the sun is radiating energy out across a giant sphere
0:12:36 > 0:12:42with a radius of 150 million kilometres surrounding our star.
0:12:42 > 0:12:44How much energy does that make?
0:12:44 > 0:12:50It's four x pi x the distance to the sun squared, which is about...
0:12:55 > 0:13:02It's 400 million million million million watts.
0:13:07 > 0:13:11That is a million times the power consumption
0:13:11 > 0:13:16of the United States every year, radiated in one second.
0:13:16 > 0:13:21And we worked that out by using some water,
0:13:21 > 0:13:25a thermometer, a tin and an umbrella.
0:13:25 > 0:13:28And that's why I love physics.
0:13:33 > 0:13:36It's a wonder of our star that it's managed to keep up
0:13:36 > 0:13:40this phenomenal rate of energy production for millennia.
0:13:47 > 0:13:51Stars like the sun are incredibly long-lived and stable.
0:13:51 > 0:13:57Our best estimate for the age of the universe is 13.73 billion years
0:13:57 > 0:14:01and the sun has been around for five billion years of that.
0:14:01 > 0:14:04That's more than a third the age of the universe itself.
0:14:09 > 0:14:13So what possible power source could allow the sun to shine
0:14:13 > 0:14:17with such intensity day after day for five billion years?
0:14:17 > 0:14:21The best way to find the answer is to go back to the very beginning.
0:14:21 > 0:14:26And it all began from, well, pretty much nothing.
0:14:32 > 0:14:35There was a time when this corner of the galaxy was without light.
0:14:35 > 0:14:38The sun had yet to begin.
0:14:47 > 0:14:52The story of how our star was born can be read in the night sky.
0:15:07 > 0:15:09If you take a picture of the Milky Way,
0:15:09 > 0:15:12then one of the first things you notice are these dark lines,
0:15:12 > 0:15:16these dark clouds running through it, an absence of stars and,
0:15:16 > 0:15:19in fact, those dark areas are called molecular clouds.
0:15:19 > 0:15:23They're clouds of molecular hydrogen and dust
0:15:23 > 0:15:28that are lying in between us and the stars of the Milky Way galaxy.
0:15:30 > 0:15:36These dark clouds contain the raw material from which stars are made -
0:15:36 > 0:15:37vast stellar nurseries
0:15:37 > 0:15:42that are amongst the coldest and most isolated places in the galaxy.
0:15:46 > 0:15:48In the centre of some of those clouds,
0:15:48 > 0:15:52the temperature is as low as ten degrees above absolute zero.
0:15:55 > 0:15:58Now, that matters because temperature is a measure
0:15:58 > 0:16:01of how fast things are moving.
0:16:01 > 0:16:04So, in these clouds, the clumps of hydrogen and dust
0:16:04 > 0:16:06are moving very slowly.
0:16:06 > 0:16:08Only in this extreme cold
0:16:08 > 0:16:13can gravity grab hold of the clouds' constituent particles.
0:16:13 > 0:16:17Over millennia, they begin to condense.
0:16:17 > 0:16:22That means that the weak force of gravity can take over
0:16:22 > 0:16:25and begin to clump the hydrogen together.
0:16:25 > 0:16:28Now, we have a name for clumps of hydrogen
0:16:28 > 0:16:31collapsing under their own gravity - stars.
0:16:38 > 0:16:42So, as those clouds of hydrogen collapse further and further
0:16:42 > 0:16:44under the force of gravity,
0:16:44 > 0:16:48they begin to heat up and eventually, in their cores,
0:16:48 > 0:16:50they become hot enough for the hydrogen
0:16:50 > 0:16:53to begin to fuse together into helium.
0:16:53 > 0:16:57The stars ignite, the clouds are no longer black
0:16:57 > 0:17:00and the lifecycle of a new star has begun.
0:17:07 > 0:17:11This very story played out five billion years ago
0:17:11 > 0:17:16when a star was born that would come to be known as the sun.
0:17:24 > 0:17:27And its birth reveals the secret of our star's
0:17:27 > 0:17:30extraordinary resources of energy,
0:17:30 > 0:17:33because the sun, like every other star,
0:17:33 > 0:17:38was set alight by the most powerful known force in the universe.
0:17:44 > 0:17:48The fusion of hydrogen into helium
0:17:48 > 0:17:52is the foundation of all the sun's power.
0:17:52 > 0:17:55Boundless energy that reaches out
0:17:55 > 0:17:59and connects this wonder to all of the worlds in its realm.
0:18:27 > 0:18:30This is the Iguazu River which flows into the Parana,
0:18:30 > 0:18:33one of the great rivers of the world,
0:18:33 > 0:18:37and it's these river systems that drain all the rainfall
0:18:37 > 0:18:41from the southern Amazonian basin eventually into the Atlantic.
0:18:50 > 0:18:53Just look how much water there is.
0:18:53 > 0:18:55Every molecule in this river,
0:18:55 > 0:19:00every molecule in every raindrop in every cloud,
0:19:00 > 0:19:04has been transported from the Pacific over the Andes
0:19:04 > 0:19:08and into the continental interior here.
0:19:08 > 0:19:11Just imagine how much energy that needs.
0:19:11 > 0:19:15And all that energy - every bit of it,
0:19:15 > 0:19:17comes from the sun.
0:19:19 > 0:19:24The sun is the power that lifts all the water on the blue planet.
0:19:24 > 0:19:27And in places, it comes down again
0:19:27 > 0:19:31to create some of the most breath-taking sights on Earth.
0:20:04 > 0:20:06This is Iguazu Falls.
0:20:06 > 0:20:08A quarter of a million gallons of water
0:20:08 > 0:20:10flow through here every second.
0:20:18 > 0:20:20The spectacular energy of the falls
0:20:20 > 0:20:25is a wonderful example of how this planet is hard-wired
0:20:25 > 0:20:28to the constant and unfailing power of the sun.
0:20:44 > 0:20:48The energy we see from the sun may seem utterly constant,
0:20:48 > 0:20:51but tiny fluctuations in its brightness can be seen
0:20:51 > 0:20:54with a digital camera and the right know-how.
0:20:54 > 0:20:58Now, it's not too difficult to take a picture of the sun
0:20:58 > 0:21:00even though it's 93 million miles away
0:21:00 > 0:21:03because it's big. Of course, you've got to be careful.
0:21:03 > 0:21:05We've got a filter on here
0:21:05 > 0:21:07that takes out pretty much all of the light
0:21:07 > 0:21:11because focusing the light from a nuclear reactor
0:21:11 > 0:21:13onto your camera or your retina
0:21:13 > 0:21:18wouldn't be a great idea, so you've got to be careful.
0:21:25 > 0:21:27I'll take a picture.
0:21:32 > 0:21:38Well, this is our picture of the sun that we took on June 20th, 2009.
0:21:39 > 0:21:42You can see it's a beautiful...
0:21:44 > 0:21:45..orb,
0:21:45 > 0:21:48with not a mark on the surface.
0:21:48 > 0:21:52I suppose that's pretty much what most people would expect.
0:21:52 > 0:21:56It's certainly what Aristotle and the ancient astronomers expected
0:21:56 > 0:22:00because they thought the heavens were perfect and unchanging.
0:22:00 > 0:22:06But, look at this picture taken on March 29th, 2001.
0:22:06 > 0:22:08You see a completely different story.
0:22:08 > 0:22:14The surface of the sun is covered in black spots - sun spots.
0:22:20 > 0:22:22Some of these vast structures
0:22:22 > 0:22:25are large enough to engulf the entire Earth.
0:22:30 > 0:22:34Space observation has allowed us to track their numbers
0:22:34 > 0:22:37as they ebb and flow across the face of the sun.
0:22:37 > 0:22:43The greater the number of sunspots, the more powerful our star becomes,
0:22:43 > 0:22:45threatening everything from astronauts
0:22:45 > 0:22:48to the electricity grids back on Earth.
0:22:51 > 0:22:55We've discovered that the sun has seasons.
0:23:00 > 0:23:04For decades, scientists have sought to understand
0:23:04 > 0:23:07how these subtle changes in the sun's power
0:23:07 > 0:23:09might be affecting the earth.
0:23:09 > 0:23:12It's a puzzle that led one man to look away from the sun
0:23:12 > 0:23:16and focus instead on the rivers around the Iguazu Falls.
0:23:18 > 0:23:22Argentinean astrophysicist, Pablo Mauas.
0:23:22 > 0:23:24It's a very large river.
0:23:24 > 0:23:26It's the fourth river in the world.
0:23:26 > 0:23:29Unlike other larger rivers than the Parana,
0:23:29 > 0:23:32for example, the Amazon or Congo,
0:23:32 > 0:23:36we have data of this river for the whole 20th century.
0:23:36 > 0:23:39So you can look back to what, about 1900 or...?
0:23:39 > 0:23:41Yes, from 1900, 1904.
0:23:41 > 0:23:43And this is because this is a river
0:23:43 > 0:23:47that can be navigated by very large ships.
0:23:49 > 0:23:53Pablo brought the statistical tools of a physicist to bear
0:23:53 > 0:23:56on 100 years worth of precious river records.
0:23:56 > 0:24:00What emerged was that the river, too, had a rhythm.
0:24:02 > 0:24:07We found that the stream flow of the river goes up and down
0:24:07 > 0:24:11and up again and down again three times during the century.
0:24:11 > 0:24:14And then we went further, trying to understand why.
0:24:23 > 0:24:26The amount of water in the Parana River
0:24:26 > 0:24:28seems to be following a pattern.
0:24:28 > 0:24:30The question is,
0:24:30 > 0:24:34what could be driving the change in these vast river systems?
0:24:39 > 0:24:44Pablo first looked to the 11-year sunspot cycle, but found no fit.
0:24:44 > 0:24:46So instead, he turned to calculations
0:24:46 > 0:24:52that described the sun's underlying brightness during the last century.
0:24:52 > 0:24:56He showed me what happened when you superimpose this solar data
0:24:56 > 0:24:58on the water levels in the river.
0:24:58 > 0:25:03You see that when the sun goes up, the river goes up.
0:25:03 > 0:25:05So what this is saying is, around 1925 or so,
0:25:05 > 0:25:07there was more solar activity,
0:25:07 > 0:25:11so the amount of, really, the solar radiation falling on the earth.
0:25:11 > 0:25:14Right, there was relatively more activity, solar activity,
0:25:14 > 0:25:16in these three periods we can see here.
0:25:16 > 0:25:20I mean, it's a beautiful correlation between the water flow,
0:25:20 > 0:25:22the flow in these rivers and the solar output.
0:25:22 > 0:25:25Yes, it is. We find it's a very striking correlation.
0:25:40 > 0:25:44Changes in the sun seem to move weather systems elsewhere, too.
0:25:44 > 0:25:47In India, the monsoon appears to follow
0:25:47 > 0:25:50a similar pattern to the Parana river,
0:25:50 > 0:25:53whereas in the Sahara, the opposite seems to occur.
0:25:53 > 0:25:56More solar activity, less rain.
0:25:57 > 0:26:03The exact mechanisms by which our star may affect Earth's weather
0:26:03 > 0:26:06remain, for now, a mystery.
0:26:06 > 0:26:10We know that the energy production rate of the sun,
0:26:10 > 0:26:15the power released in the fusion reactions at the core,
0:26:15 > 0:26:17is very constant indeed.
0:26:17 > 0:26:19It doesn't change as far as we can tell,
0:26:19 > 0:26:21and so the changes that we see
0:26:21 > 0:26:25must be to do with the way the energy gets out of the sun.
0:26:31 > 0:26:34And, whilst it's only at the tenths of a percent level
0:26:34 > 0:26:39in the amount of radiation that falls onto the surface of the earth,
0:26:39 > 0:26:43it really does reveal the intimacy and delicacy
0:26:43 > 0:26:46of the connection between the sun and the earth.
0:26:48 > 0:26:54And this connection is the secret to another of the sun's wonders.
0:26:58 > 0:27:00Of all the stars in the universe,
0:27:00 > 0:27:04we know of only one where a phenomenon has arisen
0:27:04 > 0:27:06which feeds on starlight.
0:27:12 > 0:27:15These leaves are wonderful machines,
0:27:15 > 0:27:18nature's way of harnessing the power of the sun.
0:27:18 > 0:27:20But they're fussy eaters.
0:27:20 > 0:27:24They've evolved to use just a fraction of the sunlight
0:27:24 > 0:27:27that makes its way through Earth's atmosphere.
0:27:27 > 0:27:31Here on the surface, sunlight may appear white.
0:27:31 > 0:27:34But when you pass it through a prism,
0:27:34 > 0:27:38you see it's made up of all the colours of the rainbow.
0:27:40 > 0:27:44The prism splits sunlight into its component colours,
0:27:44 > 0:27:48revealing the red, green and blue photons.
0:27:48 > 0:27:51And it's not just their colour that distinguishes them.
0:27:53 > 0:27:57The red photons don't carry much energy, there are lots of them,
0:27:57 > 0:28:00whereas the blue photons, although there are fewer,
0:28:00 > 0:28:02carry a lot of energy.
0:28:02 > 0:28:05And plants use the red bit of the spectrum,
0:28:05 > 0:28:08and they use the blue bit of the spectrum,
0:28:08 > 0:28:11but they don't use as much of the green.
0:28:11 > 0:28:14That's reflected and so that's why,
0:28:14 > 0:28:18when you look around a forest like this on a sunny day,
0:28:18 > 0:28:20you just see a sea of green.
0:28:27 > 0:28:30So the wonderful colour of the forest is all down to how
0:28:30 > 0:28:34plants have adapted to the quality of our star's light.
0:28:38 > 0:28:41And it's this ability to harvest sunlight
0:28:41 > 0:28:44which lies at the base of the complex food chain
0:28:44 > 0:28:49which nourishes, well, pretty much all life on Earth.
0:28:53 > 0:28:57Each and every one of us is sustained by the sun's light,
0:28:57 > 0:29:00an umbilical cord of sunshine
0:29:00 > 0:29:04that stretches across 150 million kilometres of space.
0:29:06 > 0:29:10But beyond the visible power of the sun lies another realm.
0:29:12 > 0:29:15These are the unseen forces
0:29:15 > 0:29:19by which it maintains influence over its domain.
0:29:19 > 0:29:23And, very occasionally, the solar system arranges itself
0:29:23 > 0:29:27so that we can glimpse this invisible kingdom with our own eyes.
0:29:56 > 0:30:00It's 5.28, so that's time of first contact
0:30:00 > 0:30:04and you can't see the disc of the sun at the moment,
0:30:04 > 0:30:07it's obscured by low cloud.
0:30:07 > 0:30:11The edge of the moon is, at this point, just beginning to touch the disc of the sun.
0:30:11 > 0:30:15You can see the sun emerging through the clouds, see the disc.
0:30:21 > 0:30:24Oh, and you can see the moon. Can you see the moon on the top?
0:30:26 > 0:30:27Oh, yeah!
0:30:37 > 0:30:41It just vanished. Can you see the rim of the moon there? Absolutely fantastic.
0:30:43 > 0:30:46Yeah? See the sun?
0:30:46 > 0:30:48CROWD CHATTERS
0:30:48 > 0:30:52You can see the celestial mechanics, the clockwork of the solar system at work.
0:30:52 > 0:30:54The alignment is absolutely perfect.
0:30:54 > 0:30:57CHATTERING STOPS
0:31:58 > 0:31:59Look at that!
0:31:59 > 0:32:05If you EVER needed convincing that we live in a solar system,
0:32:05 > 0:32:12that we are on a ball of rock orbiting around the sun with other balls of rock, then look at that.
0:32:12 > 0:32:17That's the solar system coming down and grabbing you by the throat.
0:32:18 > 0:32:22'The sun's face is now completely shrouded by the moon.
0:32:22 > 0:32:28'Only now, during totality, is the hidden wonder of the sun revealed.'
0:32:28 > 0:32:31Look, I mean, that's the sun's atmosphere, that's not clouds.
0:32:31 > 0:32:33There are no clouds there now.
0:32:33 > 0:32:39That's the solar corona. That's the atmosphere of our star shining out.
0:32:43 > 0:32:45The sun's atmosphere is strange.
0:32:45 > 0:32:51It's made up of a thin collection of charged particles, protons and electrons.
0:32:51 > 0:32:59Through mechanisms that we don't yet fully understand, the corona is much hotter than the surface.
0:33:01 > 0:33:06Here, temperatures soar to over a million degrees Celsius,
0:33:06 > 0:33:09some 200 times hotter than the visible surface.
0:33:13 > 0:33:18Each and every day, right at the very top of the atmosphere,
0:33:18 > 0:33:21some of the most energetic coronal particles are escaping.
0:33:26 > 0:33:33The sun leaks nearly seven billion tons of corona every hour into space, a vast,
0:33:33 > 0:33:37superheated, supersonic collection of smashed atoms
0:33:37 > 0:33:41that en masse are known as the solar wind.
0:33:43 > 0:33:45This is the beginning of an epic journey that will see
0:33:45 > 0:33:50the sun's breath reach out to the furthest parts of the solar system.
0:33:52 > 0:33:54Look at that!
0:33:54 > 0:33:56CHEERING AND APPLAUSE
0:34:01 > 0:34:06'All too soon, this brief glimpse of the solar wind's origin is gone.'
0:34:08 > 0:34:12It's the most incredible thing I've ever seen, actually.
0:34:12 > 0:34:15Amazing when, when the sun re-emerged from behind the moon.
0:34:15 > 0:34:17Everybody just...like that...
0:34:17 > 0:34:19Goes... Wow!
0:34:23 > 0:34:26The solar wind may be invisible to us,
0:34:26 > 0:34:31but each day, tiny pieces of our star are constantly blowing our way.
0:34:34 > 0:34:38Now, by the time the solar wind reaches the Earth, it's pretty dilute.
0:34:38 > 0:34:41You know if you were to go out into space close to the Earth
0:34:41 > 0:34:44and hold your hand up there, you wouldn't feel anything.
0:34:44 > 0:34:52In fact there are about five protons and five electrons for every sugar cube's worth bit of space,
0:34:52 > 0:34:55but still they're travelling very fast and they carry a lot of energy,
0:34:55 > 0:35:01enough energy in fact over time to blow the earth's atmosphere off into space.
0:35:09 > 0:35:14So how does life on our planet survive this lethal gale?
0:35:22 > 0:35:26'To find the answer, I need to head north.
0:35:33 > 0:35:40'On a beautiful sunny winter's day in the Arctic, it's hard to imagine that our star could be a threat.
0:35:44 > 0:35:48'But high above us, deadly solar particles are streaming
0:35:48 > 0:35:53'our way at speeds topping a million kilometres an hour.'
0:35:57 > 0:36:03Down here on the Earth's surface, we're protected from that intense solar wind that's battering
0:36:03 > 0:36:10our planet because the Earth has a natural shield that deflects most of the solar wind around it.
0:36:10 > 0:36:17And to see that shield, you just need a simple shield detector which is a compass.
0:36:17 > 0:36:21And that's because the earth's force field is magnetic,
0:36:21 > 0:36:27an invisible shell that surrounds the planet in a protective cocoon.
0:36:27 > 0:36:31It's very similar to the shape of the field around the bar magnets
0:36:31 > 0:36:36and you can see that shape by moving a compass around it.
0:36:36 > 0:36:40The compass needle follows the magnetic field lines,
0:36:40 > 0:36:44and the Earth field is actually very similar in shape to this one.
0:36:49 > 0:36:54The magnetic field emanates from deep within our planet's spinning iron-rich core.
0:36:57 > 0:37:02And it's this gigantic force field, known as the magnetosphere,
0:37:02 > 0:37:07that deflects most of the lethal solar wind harmlessly away into space.
0:37:09 > 0:37:12But the planet doesn't escape completely.
0:37:15 > 0:37:20When the solar wind hits the Earth's magnetic field, it distorts it.
0:37:20 > 0:37:23It stretches the field out on the night side of the planet
0:37:23 > 0:37:28and in some ways it's like stretching a piece of elastic.
0:37:28 > 0:37:30More and more energy goes into the field.
0:37:30 > 0:37:35Over time, this energy builds up stretching the tail,
0:37:35 > 0:37:38until it can no longer hold onto it all.
0:37:39 > 0:37:44Eventually, the energy is released, accelerating a stream
0:37:44 > 0:37:49of electrically charged particles down the field lines towards the poles.
0:37:49 > 0:37:53And when these particles that have been energised by the solar wind
0:37:53 > 0:37:58hit the Earth's atmosphere, they create one of the most beautiful sights in nature -
0:37:58 > 0:38:04the aurora borealis, or Northern Lights.
0:38:06 > 0:38:09'I've come to the far north of Norway
0:38:09 > 0:38:14'in hope of seeing the solar wind's influence on our planet for myself,
0:38:14 > 0:38:18'to see the mystical aurora for the first time.'
0:38:27 > 0:38:33Seeing the aurora on any given night is far from certain.
0:38:43 > 0:38:47'So to shorten the odds, I've recruited the help of an astrophysicist,
0:38:47 > 0:38:49'Professor Mike Lockwood.'
0:38:52 > 0:38:56So Mike, not that I'm complaining, but other than for reasons of pure enjoyment,
0:38:56 > 0:38:59why did we have to come to the Arctic Circle on snowmobiles?
0:38:59 > 0:39:02The city street lights produce a light pollution
0:39:02 > 0:39:04that actually make it hard to see the aurora
0:39:04 > 0:39:07and it's good we've come at the end of winter
0:39:07 > 0:39:10because the energy we take out the solar wind is stronger.
0:39:10 > 0:39:16Yes, so this is, I suppose then, the perfect day because we're in late March, completely blue sky.
0:39:16 > 0:39:21Fabulous. If this stays, we've got 80% chance tonight.
0:39:28 > 0:39:35Soon after dusk, and despite clear skies, there's no early performance from the aurora.
0:39:40 > 0:39:45So while we wait, Mike runs a film loop of the Northern Lights
0:39:45 > 0:39:48as seen from an extraterrestrial perspective.
0:39:48 > 0:39:52So that's a beautiful image.
0:39:52 > 0:39:54I haven't seen an image like that before.
0:39:54 > 0:39:56It was taken from above the pole?
0:39:56 > 0:40:00Yeah, that's a spacecraft in orbit around the planet, yes, going from pole to pole.
0:40:00 > 0:40:05'From space, you can really see the impact of the solar wind.
0:40:05 > 0:40:11'Its energy feeds an unbroken circuit of aurora that surrounds the pole.'
0:40:11 > 0:40:17And we will feel that it's a display put on just for us here.
0:40:17 > 0:40:22When you see the pictures from space, you realise everybody on that oval is getting the display.
0:40:22 > 0:40:28Well, my hope is that we'll be directly underneath that tiny thin band tonight here in Tromso.
0:40:30 > 0:40:37Thankfully, our luck holds and the skies remain crystal clear,
0:40:37 > 0:40:44until at last, energy brought by the solar wind sets the upper atmosphere alight.
0:40:59 > 0:41:03Absolutely amazing sight.
0:41:13 > 0:41:18Arcs, but more like curtains of green.
0:41:19 > 0:41:23It doesn't look to me like it's cascading down.
0:41:23 > 0:41:26It looks like it's rising up from the ground.
0:41:33 > 0:41:38It is quite incredibly beautiful,
0:41:38 > 0:41:42and I thought before I'd seen it that I would
0:41:42 > 0:41:45think it was all the more wonderful because I knew that I was seeing
0:41:45 > 0:41:52a visual manifestation of the earth's magnetic field protecting us from the solar wind,
0:41:52 > 0:41:55but I don't think that.
0:41:55 > 0:42:01Actually over there, there's a green shaft of light that looks like it's rising up
0:42:01 > 0:42:08out of the mountain in the distance and it looks like spirits drifting up from the mountain into heaven.
0:42:08 > 0:42:10Absolutely magnificent.
0:42:16 > 0:42:20Our environment doesn't stop at the edge of our atmosphere.
0:42:20 > 0:42:26In fact our environment stretches at least as far as the sun
0:42:26 > 0:42:29which is an obvious statement to make in the daytime
0:42:29 > 0:42:34because you can feel the heat of the sun, but in the night time, you see this other side.
0:42:34 > 0:42:37You see this unseen and constant solar wind.
0:42:42 > 0:42:47Beyond earth, the solar wind continues to race out into the solar system
0:42:47 > 0:42:54and wherever it encounters a planet with a magnetosphere, aurora spring up.
0:43:03 > 0:43:07Jupiter's magnetic field is the largest and most powerful in the solar system.
0:43:09 > 0:43:12Seen from the Hubble space telescope, the aurora here
0:43:12 > 0:43:17are a permanent fixture over the Jovian poles.
0:43:25 > 0:43:31Saturn, too, puts on an impressive display as seen in this remarkable footage.
0:43:36 > 0:43:42Eventually, though, way beyond the planets, the solar wind begins to run out of steam.
0:43:42 > 0:43:48It's travelled non-stop for 16 billion kilometres,
0:43:48 > 0:43:53over 100 times the distance of the Earth from the sun.
0:43:53 > 0:43:57And incredibly, we have a probe out there
0:43:57 > 0:44:02which is about to discover exactly where the wind from the sun ends.
0:44:10 > 0:44:16When I was about five, I collected these cards, the Race Into Space.
0:44:16 > 0:44:24It starts with Sputnik and it's a history of space, and right at the end there's the speculative stuff
0:44:24 > 0:44:31about moon base and then a manned mission to Mars, on November 12th 1981, it was going to leave.
0:44:31 > 0:44:36In there is the Grand Tour proposal by NASA to go
0:44:36 > 0:44:41to Jupiter, Saturn, Uranus, Neptune and it actually went.
0:44:41 > 0:44:44I remember in '77 being excited and watching the launch
0:44:44 > 0:44:48and thinking this is, my card has come to pass, it's come to be.
0:44:48 > 0:44:52And astonishingly, I think, we're still in contact with this thing now.
0:44:55 > 0:45:01A pair of spacecraft were sent out on the Grand Tour, Voyagers one and two.
0:45:04 > 0:45:09Both are alive and well, and Voyager one reports back to earth here.
0:45:09 > 0:45:14Now, also in my book was this picture, the Goldstone Mars station in the Mojave desert.
0:45:16 > 0:45:21And there it is, 210 feet or it was at the time this book was written.
0:45:21 > 0:45:25It's been expanded since and it's one of the few telescopes in the world that's capable
0:45:25 > 0:45:31of communicating with Voyager which is ten billion miles from the Earth.
0:45:45 > 0:45:53Today, the Goldstone station is listening out for the faintest whisper from Voyager one.
0:45:53 > 0:45:58Call 233, oh, it's almost there now, so we should be seeing it coming in.
0:45:58 > 0:46:02'Voyager is so far away that it takes the signal
0:46:02 > 0:46:08'around 15 hours to arrive, travelling at the speed of light.'
0:46:08 > 0:46:10Oh, that triangle?
0:46:10 > 0:46:12Yeah, that's it, right there.
0:46:12 > 0:46:14There.
0:46:14 > 0:46:19'It may appear as little more than a blip on a screen but for me, it's beautiful.'
0:46:24 > 0:46:27I mean, you just have to think about it, this little thing,
0:46:27 > 0:46:29it's no bigger than a double-decker bus,
0:46:29 > 0:46:36designed in the late '60s, launched in the mid-'70s
0:46:36 > 0:46:39and still functioning 32 years later,
0:46:39 > 0:46:42and good science data is still coming out of that little space craft.
0:46:42 > 0:46:45I think it's absolutely wonderful.
0:46:47 > 0:46:53Both Voyager spacecraft are constantly measuring the solar wind as it fades away.
0:46:53 > 0:47:01One day soon, they will find the place where the sun's last physical trace finally runs out.
0:47:02 > 0:47:09They'll leave the star that raised them behind and head off into interstellar space.
0:47:10 > 0:47:16But even at that place, ten billion miles away where the solar wind meets the interstellar wind,
0:47:16 > 0:47:19that isn't the end of the story.
0:47:19 > 0:47:22That isn't the edge of the sun's influence.
0:47:29 > 0:47:36'The sun has a final invisible force that reaches out much further.
0:47:38 > 0:47:43'Our star is, by far, the largest wonder in the solar system.
0:47:44 > 0:47:50'In fact, it alone is 99% of the solar system's mass.
0:47:50 > 0:47:56'It's this immensity that gives the sun its furthest reaching influence...
0:47:58 > 0:48:00..gravity.
0:48:02 > 0:48:09So its gravitational field dominates and all the planets are bound gravitationally to it.
0:48:09 > 0:48:14The Earth for example, 93 million miles away,
0:48:14 > 0:48:16also known as one astronomical unit
0:48:16 > 0:48:19so let's represent that by one centimetre...
0:48:19 > 0:48:26And the most distant planet, Neptune, 30 astronomical units so 30 centimetres.
0:48:26 > 0:48:32We then meet the Kuiper belt objects of which Pluto, the ex-planet, is a member.
0:48:32 > 0:48:36They inhabit a region around 50 astronomical units
0:48:36 > 0:48:41so that is the size of the solar system in terms of...
0:48:41 > 0:48:47well, all the planets and all the Kuiper belt objects out to Pluto, but it doesn't stop there.
0:48:49 > 0:48:55'Beyond Pluto, space is a cocktail of extremely dilute gas and dust,'
0:48:55 > 0:49:02mostly just hydrogen and helium left over from the universe's beginning at the Big Bang.
0:49:04 > 0:49:07But every now and then, you encounter lumps of ice in vast orbits
0:49:07 > 0:49:12that take millennia to loop around the sun.
0:49:17 > 0:49:21And that cloud of snowballs is called the Oort cloud.
0:49:24 > 0:49:28'And astonishingly, the sun's grip is so strong
0:49:28 > 0:49:33'that objects in the Oort cloud keep popping up all the way to out here.'
0:49:37 > 0:49:43Now, that cloud of dirty snowballs, still gravitationally bound
0:49:43 > 0:49:48to the sun, extends out 50,000 astronomical units.
0:49:48 > 0:49:49On our scale,
0:49:49 > 0:49:53that's half a kilometre from the sun and remember,
0:49:53 > 0:49:58the Earth was one centimetre away.
0:50:01 > 0:50:06This, then, is the full extent of the sun's empire,
0:50:06 > 0:50:12the lightest gravitational touch which retains a cloud of ice,
0:50:12 > 0:50:15enclosing the sun in a colossal sphere.
0:50:19 > 0:50:21Beyond the Oort cloud, there is nothing.
0:50:21 > 0:50:26Only sunlight escapes, light that will take four years
0:50:26 > 0:50:32before it reaches even the sun's closest neighbour, Proxima Centauri,
0:50:32 > 0:50:40a red dwarf star among the 200 billion others that make up the Milky Way.
0:50:40 > 0:50:44And it's by looking here, deep into our local galactic neighbourhood,
0:50:44 > 0:50:50that we're learning to read the story of our own star's ultimate fate.
0:51:09 > 0:51:16The sun's empire is so vast and so ancient and its power so immense, it seems like
0:51:16 > 0:51:22an audacious thought to think that we could even begin to comprehend its end - the death of our sun.
0:51:22 > 0:51:25But that's what astronomers are trying to do
0:51:25 > 0:51:32and many of them come here to the most arid and barren desert on earth, the Atacama in Chile,
0:51:32 > 0:51:37and that's because the skies here are some of the clearest on earth.
0:51:42 > 0:51:46'It's the end of my journey through the empire of the sun.'
0:51:46 > 0:51:51I've come to Paranal, high up on an extinct volcano.
0:51:51 > 0:51:55It's home to the world's most powerful array of telescopes.
0:51:57 > 0:52:00I've got to tell you this. This is great.
0:52:00 > 0:52:03You get important information you should know for a safe stay on Paranal
0:52:03 > 0:52:09because it's about 2,500 metres, two and a half kilometres in the air, and it says here
0:52:09 > 0:52:16that if during your stay you experience any of the following, consult a paramedic immediately...
0:52:16 > 0:52:23So there's headache and dizziness, breathing problems, ringing or blocking of the ears...SEEING STARS.
0:52:23 > 0:52:30It honestly says 'If you see stars at the Paranal Observatory, consult a paramedic immediately!'
0:52:46 > 0:52:49'Perched high above the clouds, four colossal instruments
0:52:49 > 0:52:55'make up the European Southern Observatory's Very Large Telescope, or VLT.'
0:53:02 > 0:53:06Even with the naked eye, the seeing here is spectacular.
0:53:11 > 0:53:15The first thing you notice streaking across the sky is the Milky Way.
0:53:15 > 0:53:21You can have no doubt when you look at that that we live in a galaxy of billions of stars.
0:53:27 > 0:53:30The next thing you notice, if you look a little bit more carefully,
0:53:30 > 0:53:35is the stars are not just white points of light against the blackness of the sky.
0:53:35 > 0:53:37They're actually coloured.
0:53:37 > 0:53:43You see orangey-red stars, yellow stars and bluey-white stars.
0:53:43 > 0:53:45Absolutely beautiful.
0:53:50 > 0:53:57Astronomers have gazed upon the galaxy full of stars at all stages of their lives,
0:53:57 > 0:54:04from youthful, bright stars to middle-aged yellow stars very similar to the sun.
0:54:07 > 0:54:10They've meticulously charted the nearest 10,000 of them,
0:54:10 > 0:54:16and then arranged each according to its colour and brightness.
0:54:16 > 0:54:19What emerges is one of the most powerful and elegant
0:54:19 > 0:54:24tools in the whole of astronomy, the Hertzsprung-Russell diagram.
0:54:28 > 0:54:34And so this diagram allows astronomers to predict the history and evolution of stars,
0:54:34 > 0:54:39and in particular, the future life of our sun.
0:54:39 > 0:54:42There's real structure here.
0:54:42 > 0:54:45There's this line that goes up from red stars through yellow stars
0:54:45 > 0:54:49to white stars, and this is called the main sequence.
0:54:51 > 0:54:56The sun will spend most of its life in the main sequence, steadily burning
0:54:56 > 0:55:03its vast reserves of hydrogen fuel which will last for at least another five billion years.
0:55:05 > 0:55:11But eventually the fuel will run out and its core will collapse.
0:55:14 > 0:55:17'Then something remarkable will happen.'
0:55:22 > 0:55:27The sun's outer layers will expand and its colour will shift.
0:55:27 > 0:55:34Mercury will be little more than a memory as it's engulfed by the expanding red sun.
0:55:42 > 0:55:46It will grow to 200 times its size today,
0:55:46 > 0:55:52stretching all the way out to the Earth's orbit where our own planet's prospects are dim.
0:56:03 > 0:56:08The wonder that has remained so constant throughout all
0:56:08 > 0:56:13of its ten billion years of life will end its days as a red giant star.
0:56:22 > 0:56:30For a few brief instants, it will be 2,000 times as bright as it is now but that won't last for long.
0:56:30 > 0:56:37Eventually it'll shed its outer layers and all that will be left will be its cooling core,
0:56:37 > 0:56:41a faint cinder that will glow,
0:56:41 > 0:56:43well, pretty much to the end of time.
0:56:46 > 0:56:51And all its wonders, the aurora that danced through the atmospheres of planets of the solar system,
0:56:51 > 0:56:56and its light that sustains all the life here on earth, will be gone.
0:56:58 > 0:57:02'But the gas and dust of the dying sun will drift off into space,
0:57:02 > 0:57:09'in time to form a vast dark cloud primed and full of possibilities.
0:57:11 > 0:57:15Until one day, another star will be born,
0:57:15 > 0:57:19perhaps, with a similar story to tell,
0:57:19 > 0:57:21the greatest story of the cosmos.
0:58:07 > 0:58:10Subtitles by Red Bee Media Ltd
0:58:10 > 0:58:13E-mail subtitling@bbc.co.uk