初級: TOEIC 250-545
中級: TOEIC 550-780
上級: TOEIC 785-990
The story of the Sun starts 13 billion years ago
with the Big Bang.
In an instant, the universe was born.
And since then, it's been expanding
at the speed of light.
Within the universe, there are 100 billion galaxies.
Our galaxy is but one of them.
In it, there are 100 billion stars.
And towards the outer edge of one of the spiral arms
is an almost insignificant dot:
a medium-sized, not very bright, undistinguished star.
Up close, it's a different story.
On the planets closest to the Sun,
Mercury and Venus, the heat is intense.
Their surface is scorched.
Further out through the solar system,
the Sun's rays weaken
until they are powerless against the chill of space.
The outer planets are frozen,
but in the middle lies the Goldilocks planet:
not too hot and not too cold.
In fact, it's just right.
And life has flourished in the warm glow.
All life on Earth owes its existence to the Sun.
It powers every natural system
and sustains every plant and animal.
Without the Sun, the planet would be a barren,
lifeless ball of rock.
Recognizing that power,
humans have always worshipped the Sun,
but we have also always striven to understand it.
These monuments are more than just temples.
They are calendars and observatories,
tools for studying the Sun.
And some of them are still operational.
This is Orkney.
To live here is to know the importance
of the Sun.
In the summer, the days are long
and full of light.
In December, it's a different story.
(Richards) It's midwinter.
It's about 11:00 in the morning,
and it's still not light completely.
There's a strong wind coming in off the Atlantic,
and it's cold, and it's wet.
And that's pretty much typical
of this time of the year up here.
(narrator) Yet despite the cold, in the Stone Age,
5,000 years ago, a civilization thrived here.
The island is covered in the remains of their society.
The ruins are full of mystery.
We know little about the people who lived here.
But they did leave evidence of the important role
the Sun played in their lives.
Maeshowe, 1,000 years older than the pyramids,
is one of the finest examples of Stone Age architecture.
While entering Maeshowe, I have to crouch right down
and then confronted with a passage
which seems to actually go on and on and on.
Slightly feeling the impression of going uphill, upslope.
I'm coming through, clearly, another doorway.
Suddenly, the whole thing opens out
into the most amazing chamber.
This alone is probably the highest and largest
enclosed space that neolithic Orcadians
would have experienced.
When it was excavated, when it was first entered
back in the 19th century,
the clay floor was littered
with broken pieces of human skull.
This is a place of the dead.
This is a house of the dead.
(narrator) Most of the time,
the occupants of the tomb were left in complete darkness.
Then, at sunset on the winter solstice,
the shortest day of the year, something amazing happens.
The light of the setting Sun
shines straight up the entrance tunnel
and illuminates the interior.
(Richards) Well, the significance is that
it's marking the shortest time of the year
with the least light, and from that point on,
slowly and gradually, the light is going to increase;
the days are going to grow longer.
So what's happening here is that the dead,
the ancestors, are being awoken on that shortest day.
(narrator) The winter solstice events at Maeshowe
demonstrate an intimate and precise knowledge
of the Sun's movements through the sky.
It was the first step on our journey
to understand the Sun and its many effects on us.
To complete that journey,
we've had to travel to the furthest depths of space
and to the heart of the smallest atom.
And with every closer look, the Sun has always surprised us.
To our ancestors, its power was its reliability:
always on time, never changing.
But the reality is proving to be very different.
(Mason) Most people think of the Sun as quite a boring,
constant sort of thing. (Mason) Most people think of the Sun as quite a boring,
constant sort of thing.
But in fact, it's not at all.
It's changing all the time, and if you look,
you can see those changes in a matter of minutes or hours,
and it's far from static and boring.
It's changing, and it's got a life of its own.
(narrator) Modern solar observatories
magnify and filter the Sun's light
to get past the constant glare and give a clear view
of the surface.
This is the actual face of the Sun.
It is turbulent and boiling.
Never the same from one second to the next,
the surface bubbles like a giant bowl of porridge.
Each bubble is 1,000 miles across.
The heat and light brought to the surface
raises its temperature to 6,000 degrees centigrade,
enough to vaporize solid rock.
And the Sun is huge.
You could fit the Earth inside it a million times over.
Periodically, huge explosions rip through the surface,
releasing the energy of a billion atomic bombs
All this is on the surface.
To understand the Sun,
we must know what is going on deep inside.
That is where the power is generated.
So for centuries,
scientists have been devising ways
to probe the heart of the Sun.
Some of them have been complex
and some of them very simple.
And the first step
is to figure out just how powerful the Sun is.
(Alexander) It's easy to appreciate the power of the Sun on a nice
hot summer's day, like here on the Texas Gulf Coast.
And you can feel the power of the Sun on your skin.
But man, the Sun is just, you know, the actual physics
of what's going on inside the Sun,
the power that the Sun, the energy that the Sun
is releasing, is almost beyond comprehension.
(narrator) But it is only almost beyond comprehension.
And you can measure its power output
with some simple apparatus.
(Alexander) One of the earliest experiments to try and measure
the actual power of the Sun was by astronomer William Herschel
in the 19th century,
when he had the brilliant idea of just watching
a piece of ice melt to see
how long it would take, and therefore,
from the properties of the ice,
work out how much sunlight was coming to the ground.
[beeping noise] work out how much sunlight was coming to the ground.
(narrator) As a demonstration of the Sun's power,
it doesn't look that impressive,
but Herschel realized that he could
use the time it takes to melt one bit of ice
to calculate the Sun's total power output.
(Alexander) So here we see the ice is almost completely melted.
Roughly 29 minutes, almost half an hour.
But Herschel was able
to use this experiment and the time that it took
to melt the ice to work out
some basic properties of the Sun.
(narrator) Here's how Herschel's thinking worked.
In the time it takes to melt a slab of ice on Earth,
the Sun is radiating heat in all directions,
enough to melt a complete shell of ice around it,
a diameter of 300 million kilometers.
A shell 1/2 a centimeter thick and 300 million kilometers
across contains a lot of ice,
enough to make an ice cube bigger than the Earth.
To melt that much ice in just 30 minutes
would take an energy input
of a billion billion billion watts.
It's a rough but surprisingly accurate experiment.
Modern satellite readings confirm the figures
to within a few percent.
It's an almost unimaginable amount of energy.
If we could harness the Sun's power output
for a single second,
it would satisfy the world's energy demands
for the next million years.
But it's one thing to know how much power
the Sun is producing.
It's something else to know how it's doing it.
Until the middle of the 20th century,
no one had any idea what made the Sun work.
For scientists in Herschel's time,
it was a mystery.
(Alexander) One of the issues was, of course,
what powered the Sun?
And some very clever people actually considered the fact
that the Sun might be powered by burning coal.
I mean, it seems ludicrous, but why not coal?
That was an important source of energy on the Earth
at that part of the 19th century.
(narrator) If the Sun was made entirely of coal,
there would be one unfortunate consequence.
It would burn itself out in just a few thousand years.
Today that sounds ridiculous.
But 200 years ago, it didn't seem so unlikely.
It was widely believed that the Earth
was only a few thousand years old.
But in the mid-19th century,
a new science was emerging that was painting
a very different picture of the age of the Earth.
By looking at the deepest layers of rocks,
geologists were discovering that the Earth was much older
than anyone had previously imagined.
If that was true, then the Sun
also had to have been burning for much, much longer.
(Hathaway) You can see the strata in the lines
in the rock in back of you that represent hundreds
of million years of geological history.
The top of Sacramento Peak up beyond this,
we find fossils that are 300 million years old.
Below Sacramento Peak, we've got more than a kilometer
of these strata that are far older than that.
From the age of these strata, geologists knew that the Earth
was at least a billion years old.
At the same time,
astronomers thought that the Sun was only 10,000 years old.
If the geologists were right,
then astronomers had to find some other source
for the Sun producing its energy.
(narrator) The search for the source of energy
that could power the Sun for billions of years
lasted for nearly a century.
Eventually, scientists would find the answer in the forces
that hold atoms together
and in the nature of matter itself.
But first, you have to know what the Sun is made of.
To find that out,
you need to take a very close look at sunlight.
(Hathaway) When you take the light from the Sun
and pass it through a prism-- spread it out into the colors--
as you look through it,
you notice that it isn't uniform,
that there are places that are darker.
Each of those dark lines is due to
a specific chemical element.
Each element has its own series of lines
that are specific to it.
(narrator) Each chemical element absorbs light
at specific frequencies,
removing a strip from the spectrum.
As the light passes through the Sun,
all the elements leave their mark.
So when the light arrives at the Earth,
it contains the complete chemical formula
of the Sun.
(Hathaway) If we take the spectrum
and spread it out to fine details,
and what we've done here is stack up pieces
of the spectrum one on top of each other,
you see all of these dark areas.
The key to figuring out how much
of these elements are there
is the breadth and the depth of the light.
How dark is the line and how broad is it?
(narrator) The composition of the Sun lies in this bar code.
All the thin lines are caused by tiny amounts
of complex elements,
metals like iron and magnesium.
But there are three very deep broad lines,
and they are all caused
by an enormous amount of a single element.
There's some helium and traces of heavy elements,
but over 90% of the Sun is hydrogen.
It's the simplest and most common element
in the universe.
The secrets of the Sun's power must lie in this gas.
Look carefully into the night sky
and you'll see huge clouds of hydrogen
floating in interstellar space.
These are nebulae,
and they can be hundreds of light-years across.
They are some of the brightest areas
in the sky,
lit up by the intense light of newly formed massive stars.
In them, we can see stars being born.
It is to areas like this
that astronomers turn their telescopes
when they want to study how our Sun was formed.
There she is; okay.
So now let's recenter on her.
(narrator) By studying different nebulae, it's possible to piece together
the stages in which stars are made.
And it all starts in a cold, dark cloud,
floating around waiting for something to happen.
(Scowen) Cold clouds like this are actually quite stable.
They will sit there for a very, very long time;
for thousands and, some cases, millions of years,
before they'll actually do anything.
What you need to do to get the star formation process going is,
you need to kick it with something.
That can be an impact on the cloud from one side
by a supernova blast wave.
A massive star nearby has gone phoom
at the end of its life, and that sends out
in all directions very energetic compression waves
that hit the gas and compress it.
(narrator) The shock waves knock the cloud out of balance,
causing localized clumps of hydrogen to form.
These are the seeds from which stars grow.
The increased gravity of the seeds
sucks in more and more hydrogen in a runaway process
that lasts for a million years.
As more hydrogen is squeezed into the clumps,
the temperature rises.
They are not yet producing light,
but they are well on their way to becoming stars.
As they grow bigger and bigger, they start to spin
and throw out a disk of debris
that will coalesce to form a solar system.
(Scowen) This kind of process is exactly the kind of process
that would have formed our solar system.
When we look at our solar system,
all of the planets
rotate around the Sun in the same direction,
and they all are in the same plane,
the same flat sheet around our Sun.
And this is exactly a consequence of the fact
that the early solar system formed out of a broad disk.
(narrator) With the solar system in place, all that is left
is for the young star to light up.
When it happens, it is sudden and irreversible.
Ultimately, the process starts.
And because it liberates so much energy
with that first fusion, then the process takes off.
It lights up a large area,
and it starts to shine on its own
within a matter of minutes.
It's a very quick process.
(narrator) In that first burst of light,
the star has begun its lifelong activity
as a factory for making other chemical elements.
Every atom in everything around us
was made in the heart of a star, and all were made
from the same starting ingredient.
The simplest element that we have is hydrogen,
and it's actually the building block
for all the other elements that we have.
(narrator) In the heart of the Sun, hydrogen nuclei--protons--
are stuck together to make helium.
It sounds straightforward,
but it can only happen in the most extreme conditions.
In order for these protons to come together--
because they're both positively charged,
they don't want to come together--
they've actually got to be pushed together.
In order to do this,
you need very high temperatures so they're moving very fast,
and you also need very, very high pressures.
(narrator) The only part of the Sun
that is hot and dense enough is the core,
an area that contains over half the star's mass
in less than 2% of its volume.
Here, at 15 million degrees,
the protons are bashed together so hot that they fuse.
A helium nucleus is a tiny bit lighter
than the combined mass
of the four protons it is made from.
And as Einstein tells us,
it is that tiny bit of lost mass that provides the power.
(Mason) Energy is equal to mass times the speed of light
times the speed of light.
Now, the speed of light is a very, very big number.
So if we just take a small amount of mass,
we get a huge amount of energy.
And that's the energy which actually powers our Sun.
(narrator) Every second, 5 million tons of the Sun
is converted to pure energy.
And although it has been burning for 5 billion years,
it is only halfway through its supplies of hydrogen.
The light produced in the core must travel
over half a million kilometers to the surface,
and it does so very slowly.
The heart of the Sun is so dense
that the speed of light
is less than one millimeter a second.
It can take 200,000 years for the light to travel
from the core to the surface.
It takes just another eight minutes
to get to the Earth.
This is what the power of nuclear fusion looks like
from 150 million kilometers away.
This is what it looks like close up.
The H-bomb was man's first attempt
at recreating the Sun on Earth:
a1 balloon full of hydrogen
squeezed until it released its energy.
In contrast to its destructive power,
it's long been realized that controlled nuclear fusion
could solve the world's energy problems.
It has been one of the holy grails
of science for half a century.
(male announcer) This kind of power, the H-bomb,
is a man-made version of this, the Sun.
Britain announced that she could produce
this power in the laboratory in a machine called ZETA,
that is a real prospect of unlimited energy
from controlled thermonuclear fusion.
(narrator) Unfortunately, it wasn't that easy.
But now, nearly 50 years later,
in the same laboratories in Oxfordshire,
scientists are finally
managing to create their own star on Earth.
MBI, ready when you are.
Shot one, four.
Six, five, eight.
Starting shock in five seconds.
(narrator) It might not seem like much, but slowed down by 300 times,
the pictures reveal how the gas plasma
is being squeezed and heated to create
the most extreme conditions in the solar system.
Plasmas, I was like to think of as being like naughty children.
They're full of energy, and they want to misbehave.
And it's our job to try and control
(narrator) For the particles to fuse on Earth,
the temperatures need to be raised
to ten times those found at the heart of the Sun.
Bombarding the gas with a stream of fast neutrons
raises the temperature to over 100 million degrees.
Only then can the energy of nuclear fusion be released.
After years of learning to control the plasma,
scientists now believe they are within sight
of harnessing the Sun's power.
(Kirk) The aim of it is to be able to produce cheap, clean,
and, effectively, an inexhaustible supply
of electricity for future generations.
(narrator) This is only a small experimental reactor.
It can only run for a few seconds
and sucks up more energy than it creates.
But the next generation of bigger reactors
is already being built.
When operational, they will produce
ten times more energy than they use.
They will be stars on Earth,
power stations that won't deplete
natural resources or produce dangerous waste products.
It sounds great,
but re-creating the Sun isn't easy,
and it may be another 50 years
before the fusion power station becomes reality.
Until then, we'll just have to make due
with the real thing, but that's not so bad.
Just seeing sunlight is enough to cheer us up.
(Farmer) Well, many people think it's the warmth of the Sun
that is associated with us feeling good.
And of course, that's true.
But in fact, research has shown
that it's not really the warmth.
It's actually the light that's important.
(narrator) Sunlight controls our daily cycle
making sure we wake up in the morning
and go to sleep at night.
When there's not enough light
those patterns get disturbed, with miserable effect.
It's a clinical fact that depression is more common
in winter because of the lack of sunlight.
They call is SAD: seasonal affective disorder.
(Farmer) Seasonal affective disorder is a depressive illness
that starts during the autumn and early winter
and usually goes away completely
during the spring and early summer.
Some people feel quite miserable and depressed and gloomy
during the winter months.
And some people, a small proportion,
will go on to develop clinically significant depression
which requires treatment.
(narrator) This is Rattenberg, a fairy-tale Austrian village
cursed by lack of sunlight.
Due to a quirk of geology,
it gets no sunlight at all between November and February.
During those winter months, the Sun never rises high enough
to clear the brow of Rat Mountain.
And the town lies in permanent shadow,
while its neighbor across the river
basks in the sunshine.
(Altenburger) In winter, of course, it's very cold; it's shadow.
And as you can imagine, it's cold; we are freezing.
And if you want to have some Sun,
you have to move to the next village.
It makes you happier to sit in the sunlight
and not too freeze in the shadow.
(narrator) Frozen and in the dark,
the residents have been forced to take desperate measures
to bring some light into their lives.
Helmar Zangerl is a lighting expert who specializes
in bringing natural light
into some of the world's biggest buildings.
He may be the salvation of Rattenberg.
(Zangerl) Evolutionary speaking,
man has adapted to natural light and has adapted to the Sun.
And if you deprive man of the Sun, clearly,
it's a different quality of life.
How do you feel if you sit for one week
in a place with fog?
And how do you feel when you sit for one day
in a place where the Sun shines?
I personally feel so much happier
in sunshine; I can tell you that.
(narrator) The solution for Rattenberg is simple:
steal some of the sunlight
from the other side of the valley.
Eventually, a huge system of mirrors
will reflect the light of the Sun
to a second set of mirrors on the castle above the town
and then reflect it down into the streets
to brighten the lives of the citizens of Rattenberg.
(Zangerl) Well, the main effect
for the people in town will be that part of the facades
of the buildings and part of the street,
at least of the main street, will be brightly illuminated
and will clearly be recognized as sunlight.
(narrator) It sounds crazy, but it's true.
People will go to extraordinary lengths
for a bit of sunlight.
But the Sun is much more than a giant lightbulb.
There are other forces at work in the Sun...
forces that change over minutes and over years,
forces that tear the surface apart.
We are only now beginning to understand these forces
and the effects they have on the Earth.
But we've known about them for hundreds of years
because the Sun gets spots.
Sunspots are dark regions on the surface of the Sun,
typically about the size of the Earth in terms of area.
Here's a live shot of one today.
Unfortunately, we've got a very windy day
with high, thin clouds, so the picture's bouncing around
and not very sharp,
but with very high resolution images,
we can see detailed structure in the sunspot.
The inner part of the sunspot, the dark umbra, as we call it,
is dark only in comparison to the rest of the Sun.
It's actually bright enough that it would blind you
if you looked at it alone.
(narrator) The spots are not static.
These video images show the edges crawling,
almost as if it was alive.
The movements of sunspots have been studied for 400 years,
ever since Galileo trained his telescope
on the Sun and made the first crucial discovery
about its behavior.
Surprised to see black dots creeping over the surface,
he kept track of them over a number of days
and found that they were all moving
in the same direction. and found that they were all moving
in the same direction.
To Galileo, the meaning was clear.
The Sun was rotating and was turning faster
at the equator than at the poles.
It was a discovery that was to prove critical
in our understanding of how the Sun works.
Ever since Galileo, records have been kept
of the coming and goings of sunspots,
and variations soon became clear.
Sometimes the Sun is covered in hundreds of spots.
Other times, there are none at all.
And after a while,
a pattern emerged.
(Hathaway) If you observe sunspots over several years,
they come and go with about an 11-year cycle
from solar minimum-- where there can be
no spots at all on the Sun for weeks or months at a time--
to a maximum where you can have
100 spots visible on the surface of the Sun,
and then the decline again, usually over
about six years or so to back to minimum.
(narrator) Until recently, no one knew what was driving
the solar cycle or where sunspots came from.
But people had always suspected
that the scars on the Sun's surface
had an effect on the Earth,
but no one could quite put their finger on what it was.
(Hathaway) It has been correlated
with all kinds of different things:
the price of wheat, the thickness of fur on animals.
I'm inundated with it every day.
I got a guy that comes to my website
to try to predict the stock market
from the daily sunspot areas.
He said, "Oh, you didn't post them today.
I got to know."
I said, "So are you making money or what?
I want some if you are."
(narrator) One effect sunspots do have on the Earth
is on the climate.
But it is a subtle effect.
Its greatest impact was only noticed
300 years after the event.
It was discovered in Greenwich
by the astronomer Robert Maunder,
who was studying the hundreds of years of sunspot records
held at the Royal Observatory.
(Massey) And in the late part of the 19th century,
he became particularly interested in the sunspots.
And he discovered that there had been
this peculiar effect in the second half
of the 17th and 18th centuries,
when the sunspot numbers diminished to, really,
a fraction of what they are today.
And he described this as the Maunder Minimum.
(narrator) For 70 years, from 1645 to 1715, sunspots disappeared.
It was as if the engine
that drives the solar cycle had stopped.
And it correlated almost exactly
with the last period of prolonged cold
to strike the Northern Hemisphere.
They call it The Little Ice Age.
What's interesting about a period like
the little Ice Age is that you don't necessarily
see a very large dip in temperatures,
but nonetheless, even a degree or two is enough
to see some really quite dramatic effects,
like pack ice advancing south from the North Pole,
like the Viking colonies in Greenland being wiped out
by the change in climate
and the population of Iceland falling by half.
Now, in Britain, the weather was cold enough
that the temperatures would regularly freeze in winter,
and one of the classic depictions
of life at the time is frost fairs,
when the population would hold a fair on the frozen river.
So things really must have been
a lot harsher than they are today.
(narrator) When the sunspots disappeared,
something on the Sun changed that cooled the Earth down.
But it wasn't that the solar output changed.
No matter how many sunspots there are,
the Sun doesn't get any hotter or brighter.
So the spots must have another effect,
and to see it,
we need a different way to look at the Sun.
It's not just heat and light that the Sun
is throwing at the Earth.
As every sunbather knows,
there's ultraviolet light too.
Enough UV reaches the surface to burn our skin,
but it is only a fraction of the Sun's UV output.
The rest is filtered out by the atmosphere.
It means we don't get a complete picture of the Sun
from the Earth.
To see it in all its glory, you have to go into space.
From here, you can really see the changing Sun.
In the extreme UV,
the sunspots burn a brilliant white.
In the X-ray frequencies, they look even more dramatic.
Huge plumes of super-heated gas spout from the spots.
(Mason) When you're seeing the visible,
you're really seeing the surface of the Sun.
But when you see the ultraviolet or the X-rays,
you're actually seeing that very hot atmosphere,
and that's about a million degrees,
whereas the surface is about 6,000 degrees.
So you're seeing a different part of the Sun,
and you're seeing a part that's constantly changing.
(narrator) These phenomenal displays of solar power
were only discovered in the 1970s
by the astronauts on Skylab.
No one had seen the Sun like this before.
Since then, a number of space telescopes
have been deployed whose sole purpose
is to look at the Sun.
The most used is SOHO,
the Solar and Heliospheric Observatory.
It sits a million miles away from the Earth
at the Lagrangian point where the gravitational pull
from the Earth and the Sun is equal.
Fixed in space, it has an uninterrupted view
of the Sun and its tantrums.
(Harra) It has completely transformed our understanding.
You can essentially see right from inside the Sun
right through to the coronal mass ejections
as they're leaving the Sun.
So you're seeing way out to 30 solar rediae.
(narrator) SOHO has played a key role in understanding
the explosive power of the Sun.
By blocking out the disk, it simulates an eclipse,
revealing the outer atmosphere and the true scale
of the Sun's largest eruptions.
These are solar flares and coronal mass ejections,
and they erupt from the heart of sunspots.
The temperatures in a solar flare
will be tens of millions of degrees.
So it's an extremely hot, very dramatic change
in temperature over a short period of time.
When they erupt completely,
you can get masses which are roughly the mass
of Mount Everest being flung out into the solar system.
(narrator) At solar minimum, flares are infrequent.
But every 11 years,
when the cycle peaks at solar max,
the Sun puts on the best firework display
in the solar system.
Solar astronomers are now beginning
to understand the cause of these explosions.
They are not caused by the power of fusion.
There is another force at work.
It is the force of magnetism.
The Sun is covered in a complex network
of magnetic fields.
A magnetic map shows a familiar patchwork
on the face of the Sun.
The areas of the strongest fields
coincide exactly with the position of sunspots.
Here, the magnetic field strength
can be amplified 10,000 times.
(Alexander) It turns out that the regions of the strongest magnetic field
on the Sun are in the sunspots.
And in the units that we used, sunspot magnetic fields are
roughly 1,000, 2,000, maybe 3,000 gauss.
But if you look at magnets like the ones I'm playing with here,
the magnetic field in these magnets
is about 1,000 to 1,500 gauss.
So these have roughly the same magnetic field strength
as a sunspot.
The key difference, of course,
is that a sunspot's an awful lot bigger,
and so the total energy
or the amount of energy in the magnetic field
on the Sun is enormous.
But the field strength in any given location
is something you can hold in your hand.
(narrator) Sunspots are just the visible effect
of magnetic fields so strong that they can prevent
the heat and light rising from the Sun's interior.
With the right viewing equipment,
you can even see the magnetic fields.
Magnetic loops arch off the surface.
Like iron filings around a bar magnet,
their shapes are mapped out
by plasma heated to a million degrees.
The largest are 200,000 kilometers high,
and they are packed full of unstable energy.
(Alexander) When you add up the total energy content
in these loops, it comes out to, roughly,
10 to 21 joules of energy,
and that's roughly ten times
the annual energy consumption of the United States.
Of course, we can see thousands
of them at any one time.
The loops are caused by the twisting
of the Sun's basic magnetic field.
Because the Sun rotates faster at the equator
than at the poles,
it drags the field lines with it,
stretching and twisting them like elastic bands.
As the solar cycle goes on,
the fields get more and more twisted
and break through the surface.
Until its solar max,
the whole Sun is covered in loops,
stretched to breaking point.
Solar flares are what happen when the strain gets too much
and the loops snap.
Basically, all that energy comes out
of the catastrophic release of energy
that's been stored in the magnetic fields.
So like if you wind up an elastic band too much,
if you let it go with your fingers,
that elastic band flies across the room.
(narrator) When the energy bound within sunspots is released,
billions of tons of plasma
are fired far into space at huge speeds,
and sometimes they are aimed straight for the Earth.
The flares fly through space for two days.
When they reach us,
the Earth's own magnetic field deflects most of the blow.
But it is the impact on the magnetic field
which affects the Earth.
It's called space weather,
and the best of its effects are magical.
The auroras, dancing displays of celestial light,
are caused by particles from the solar storm
smashing through the magnetic field at the poles.
When they strike the upper atmosphere,
they light up the polar skies.
In the strongest storms at the peak of the solar cycle,
the northern lights can be seen as far south as Athens and Cuba.
But the buffeting of the magnetic field
has other unseen effects.
Migratory animals that navigate using the magnetic field
can lose their bearings.
Racing pigeons don't come home.
And whale strandings have been seen to increase
with solar activity.
But most worryingly for us
is the effect that the disrupted magnetic field
can have on electronics.
The strongest storms can damage or destroy satellites,
with devastating effects.
We're sort of more sensitive to the Sun
than we probably realize,
because when the Sun releases this magnetic energy
in the form of solar flares and coronal mass ejections,
maybe you don't notice it at first,
but a little crackle on your cell phone
or your cell phone going out may actually be caused by
enhanced activity on the Sun.
(narrator) Mobile telephones, television,
airplane navigation, even weapons guidance systems
all rely on satellite communication
and all can be disturbed by space weather.
The more we are reliant on these systems,
the more we will feel the effects
of the Sun's tantrums.
But we still don't understand
all of the effects of space weather.
No one can explain the effect on the climate
or why the disappearance of sunspots
should cause an ice age.
It may not matter.
The small effect that solar variation has
on the climate has long since been drowned out
by man-made global warming.
As the world warms up,
the Sun may yet prove an unlikely source of cooling.
The greenhouse effect could be stopped
by harnessing its heat.
The American Indians of the Southwest deserts
have understood the importance
of living sustainably with their environment
for hundreds of years.
(Honawa) We have the natural disasters,
like the big old fires, the volcanoes erupting,
the big old earthquakes, the tsunami.
That's the Earth telling us that it's getting pretty tired.
It's warning us that we need to slow down.
On the mesas of Arizona,
far beyond the reach of the electricity grid,
lies Old Oraibi,
the oldest occupied settlement in North America.
For 1,000 years, the Hopi Indians have lived here
in harmony with their environment.
But that doesn't mean that they have to live without
the conveniences of modern life.
They have just realized that they are already getting
all the power they need.
Under the clear skies of the desert,
a family can be supplied with electricity
from a couple of solar panels.
(Honawa) Being that we pray to the Sun every day,
it's got our heartfelt desires.
He receives it every day.
We thought the best source of energy
should come from the Sun.
(narrator) A few miles across the desert,
the idea is finally catching on
with the rest of American civilization.
But naturally, it's on a much bigger scale.
These are Stirling dishes,
the daddy of solar power systems.
And they may be about to solve
the energy crisis facing the cities of the American West.
(Osborn) People want to run their air conditioners,
their computers, their lights, during the day,
and we run out of energy.
We have a solar furnace 90 million miles away
that provides life for all of Earth.
In the past,
we've been unable to harness that potential
because the efficiency, the cost, et cetera
of the system just didn't make it viable.
What's changed is technology.
The technology now allows us
to build large-scale, highly-efficient
(narrator) Each dish tracks the movement of the Sun across the sky,
focusing the heat onto a single point,
where it is converted to electricity.
They are twice as efficient as any other solar power system.
With one, you could power a small village.
A field of them could power a city.
Each system produces about 25 kilowatts,
which is enough to power about ten homes.
However, we plan to deploy these
on a large scale-- 20,000 of these--
which is massive, about 500 megawatts,
which is the equivalent to a coal-fired plant
or maybe even a nuclear plant.
(narrator) The ink is just drying on the contract