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 shapes all this
also shape the worlds beyond our home planet.
I think we 're living through the greatest age of discovery
our civilization 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! - Oh, my!
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 Sun rise 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 practiced 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 6:24 a.m.,
the Moon will cover the face of the Sun and there will be a total solar eclipse.
I could tell you that in 2904
there will be five solar eclipses on the Earth.
And I could tell you that on July 16, 2186,
there will be the longest solar eclipse for 5,000 years, 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 77th century.
These laws allow us to predict exactly
where each world will be for centuries to come.
Anad 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.
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' moon, Phobos,
as it makes its way across the disc of the Sun.
So this is a solar eclipse, a 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.
Now, 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 are 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 e vents.
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, 73 billion kilometers away from Earth,
the Sun is just another star.
Uranus is 70 billion kilometers 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.
Two hundred and thirty million kilometers 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, 758 million kilometers out,
we continue to head to the heart of the solar system.
Mercury is the closest planet, just 46 million kilometers out.
It spins so slowly
that sunrise to sunrise lasts for 776 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 75 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 endeavor
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 tinful 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 meter of the surface.
It turns out, on a clear day, when the Sun is vertically overhead,
that number is about a kilowatt.
That's 10 100-watt bulbs can be powered by the Sun's energy
for every meter 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 kilometers away from the Sun.
So actually the Sun is radiating energy out
across a giant sphere
with a radius of 150 million kilometers
surrounding our star.
How much energy does that make?
It's four times pi, times the distance to the Sun...
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 center 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 cloud's 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 life cycle 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 Iguagu 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 breathtaking sights on Earth.
This is the Iguagu 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 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.
Take a picture.
Well, this is our picture of the Sun that we took on June 20, 2009.
And you 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 29, 2001.
You see a completely different story.
The surface of the Sun is covered in black spots, sunspots.
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 lead one man to look away from the Sun
and focus instead on the rivers around the Iguagu Falls,
Argentine 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 the Congo,
we have data of this river for the whole 20th century.
So you can look to, what, back to about 1900?
Yes. From 1900, 1904.
And this is because this is a river
that can't be navigated by very large ships.
Pablo brought the statistical tools of a physicist
to bear on 700-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 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 describe the Sun's underlying brightness during the last century.
He showed me what happens 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 is a beautiful correlation between the water flow
- flowing in these rivers... - Yes, it is.
- 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 Paranad 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 real green and blue photons.
And it's not just their color 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.
What 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 color 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 pretty much all life on Earth.
Each and every one of us is sustained by the Sun's light,
an umbilical chord of sunshine
that stretches across 750 million kilometers 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 the 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. You can see the disc.
Oh, you can see the Moon. Can you see the Moon on the top?
Oh, yeah.
It's just vanished.
You can see the limb of the Moon there. Absolutely fantastic.
Very good.
Yeah? You see the Sun?
You can see that the celestial mechanics,
the clockwork of the solar system at work.
The alignment is absolutely perfect.
Look at that.
You know, 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 a hidden wonder of the Sun revealed.
Now, look, that's the Sun's atmosphere. That's not clouds.
Now, 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! - Oh, my!
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 the Sun re-emerged from behind the Moon,
everybody just, like that, goes up to it.
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 traveling 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 kilometers an hour.
Down here on the Earth's surface,
we're protected from the 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 a bar magnet,
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 on to 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 energized 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 the 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.
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?
We needed to get out of the city
because the 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 actually, the energy we take out of the solar wind
is a little bit 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.
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 you feel that it's a display put on just for us here.
But when you see the pictures from space,
you realise everybody on that oval is getting the display as well.
Well, my hope is that we'll be directly underneath that tiny, thin band...
- Yes. - Tonight here in Tromsø.
Thankfully, our luck holds and the skies remain crystal clear
until, at last, energy brought by the solar wind
sets the upper atmosphere alight.
An absolutely amazing sight.
Ah! It's 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'd seen 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 day time,
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 traveled non-stop for 76 billion kilometers,
over 700 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 the history of space.
And right at the end, there's this speculative stuff
about moon base and a manned mission to Mars,
on November 12, 1981, it was gonna leave.
In there is the Grand Tour, a 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 1 and 2.
Both are alive and well, and Voyager 1 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.
Some 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 10 billion miles from the Earth.
Today, the Goldstone Station is listening out
for the faintest whisper from Voyager 1.
Strictest call 233.
Oh, shoot, it's almost there now, so you should be seeing it coming in.
Voyager is so faraway that it takes the signal
around 15 hours to arrive, traveling at the speed of light.
- Oh, that triangle? - Yeah. That's it right there.
- There it goes. - Yeah. Yeah.
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 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 some good science data is still coming out of that little spacecraft.
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, 10 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, 95 million miles away,
also known as one astronomical unit.
So let's represent that by one centimeter.
And the most distant planet, Neptune, 30 astronomical units,
so at 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 kilometer from the Sun.
And, remember, the Earth was one centimeter 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,
that 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 in Paranal
because it's about two and a half thousand metres
or two and a half kilometers in the air.
And it says here that,
"If during your stay you experience any of the following,"
"consult a paramedic immediately."
It says, "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.
And 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 colored. You see orangey-red stars
and yellow stars and bluey-white stars.
Absolutely beautiful.
Astronomers have gazed upon a 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 color 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.
This is called the Main Sequence.
The Sun will spend most of its life on 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 color 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 10 billion years of life,
will end its days as a red giant star.
For a few brief instants, it'll 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'll be left will be its cooling core,
a faint cinder that will glow
well, pretty much till the end of time.
And all its wonders, the aurora that danced
through the atmospheres of the 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.