The Planets (2017) s01e05 Episode Script
Star
In 1973, nine astronauts were sent to live and work in the world's first space station - Skylab.
Their mission was to observe the sun, free from the Earth's distorting atmosphere.
They witnessed what no one had seen before, a sun more powerful than they had ever imagined.
To our ancestors, the sky was a patchwork of puzzles.
At night, it was brimming with pinpoints of light - stars.
Then there was the sun, whose arrival banished the stars and brought warmth and light.
It was hailed as the giver of life, the first god.
This is the story of mankind's struggle to see behind the glare and glimpse the truth about the sun and how we came to understand its power and its role in the universe.
(Carnival music) In February 1998, the Caribbean island of Guadeloupe geared itself up for a rare celestial event.
For a few minutes, day would become night during a total eclipse of the sun.
This was Francisco Diego's tenth eclipse.
As a boy, he was deeply affected by his first.
It started a lifelong fascination with the sun.
'The sun was perceived as an immaculate' gold disc, perfect.
It was a religious belief.
Everything was perfect in the sky.
The sun was the most perfect circle, with no blemishes or structure.
A perfect, flat, golden disc.
'It was the sun god for many religions.
' The sun remained a symbol of perfection until a 17th-century Florentine called Galileo first pointed a telescope at the sky, and instantly recorded the first scientific milestone.
'Galileo applied the telescope for the first time, 'and discovered the sun wasn't perfect.
'It had sunspots.
'That was a major revolution in philosophy and science.
' Galileo watched the sunspots move across the sun's surface and realised it was spinning.
It was the first of many secrets sunspots would reveal.
Galileo's insight heightened speculation about the true nature of our sun.
But for two centuries, astronomers were frustrated by its blinding disc.
What were sunspots? What other landscapes existed on the sun's surface? What was the source of its power? There were moments, scientists realised, when the sun offers a rare and special opportunity.
Roughly six times every decade, somewhere around the world, the sun passes directly behind the Moon.
If the sun's this big, Earth's a little ball of 3-4mm in diameter and the Moon is even smaller.
It's a quarter of the Earth, 400 times smaller than the sun.
The fantastic coincidence is that the sun is 400 times further away than the Moon from us, so we see both more or less the same size.
(Man ) One minute! For 4 hours, Francisco watched the Moon creep into position.
(Man ) No filters! He came halfway round the world for just four minutes of totality.
But where the sun is concerned, dedication has never been any guarantee of success.
(People shout and cheer) Francisco got just a few moments to glimpse the hidden sun.
We lost it.
No corona.
Like many astronomers before him, Francisco was thwarted as the clouds rolled in to spoil the party.
Douglas Gough is a leading solar scientist.
To see his first total eclipse, he had travelled to Indonesia.
The government had declared it illegal to watch the eclipse, at least for the Indonesians.
They had to watch it on TV or go to the mosque and pray the dragon would spit the sun out.
They believed that was happening.
I was standing on a road, and a little boy came up to me.
I gave him a dark film, to look at the sun.
An old man of 70, the head of the village, came too, and the three of us saw a fantastic eclipse.
A total eclipse reveals the sun's corona, an outer layer normally lost in the glare.
'An eerie feeling, and almost total silence.
'The only thing we heard was the chanting from the mosques.
' This is what early astronomers travelled the world to see.
Within the corona were seemingly burning clouds.
The surface looked smothered in a complex, raging atmosphere.
'You realise, seeing these things, 'the sun's active, not a passive ball of gas.
'It's churning away.
Interesting things are happening.
' Discovering new things is exciting.
That's why explorers explored places no man had been before.
On Earth, there's little left, so we go into the universe.
Seeing the sun, peeling off a layer of mist, of lack of understanding, and seeing how something works, is an amazing experience.
The rarity of a clear eclipse gave scientists few chances to study these prominences.
In the 19th century, Father Angelo Secchi, the Vatican's chief astronomer, caused a revolution in the way we looked at light.
From an observatory above his church, he pioneered a new branch of science - spectroscopy.
His spectroscope split sunlight into its constituent colours, then magnified the light in one region.
It was possible to see the sun's edge, without relying on an eclipse.
Spectroscopy revealed a solar surface of astonishing complexity.
You were no longer dazzled by the sunlight.
You could see the things you can see at the edge of the sun during an eclipse.
Soon astronomers were studying the body of the sun.
The sunspots were Earth-sized tears in the surface.
Like windows on a mysterious interior.
The surface itself bubbled before their eyes.
Soon they were cataloguing the chemicals in the sun.
Dark bands in its spectrum meant hydrogen, calcium, iron.
Astronomers discovered an alien element, unknown on Earth.
They named it after Helios, the Greek sun god.
Helium.
When Secchi turned his spectroscope to the stars, he made his most profound discovery.
He recognised the pattern immediately.
Their chemistry was identical to the sun.
One great mystery of the heavens was resolved.
Our sun was a star.
The sun was a star, and one realised it belonged to the family of stars.
'Scientifically, that's fantastic, 'as we want to know what the universe is like.
'By studying the sun, we study a typical star.
' In the '40s we got our first inkling of how deadly a typical star can be.
As the first rockets rose to the fringes of space, they were scorched with radiation.
Our atmosphere lets heat and light through, but shields us from X-rays, gamma rays and ultra-violet light from the sun.
Soon a man was to brave this deadly radiation, and come face to face with a star.
Alexei Leonov.
'Three, two, one, zero.
' In 1973, a solar laboratory was sent to study the sun directly from space.
But the sun didn't give up its secrets lightly.
'When Skylab was launched, it had a heat shield, 'that was to open up after it got into orbit.
' Sixty seconds into flight, that heat shield popped open.
It's still in the air stream, so the air stream tore the heat shield off, and unlocked both solar wings.
Conrad had been on the Moon when he became crew leader on Skylab.
Their home was no longer protected by an atmosphere, and temperatures started to soar.
They had to find a way of shielding the station from the sun's excesses.
'We got this temporary heat shield rig, 'which we could rig from inside, through an air lock.
' We could push, like an umbrella pole, and mylar sheets popped open like an umbrella.
'Then we could pull it to where it was offset a few inches.
'It did make the temperature go down immediately.
' As the temperatures dropped, the crew went into the observatory.
They had to get used to life in a weightless environment.
At first, nausea prevented all but the most hardy from eating.
That problem quickly passed.
Soon space didn't seem so bad.
Then, with no distorting atmosphere to blur their sights, the most extensive period of solar observation ever began.
'The Skylab flight is very dear to my heart.
' I know a lot of people don't understand that It means more to me than going to the Moon.
Part of that was being able to run the solar telescope and know we were bringing back a tremendous amount of information that nobody had before in great quantities.
When I switch to the two positions called h-alpha, these words stand for hydrogen-alpha, called that because the light here comes from light from hydrogen atoms in the sun's atmosphere Viewing the sun in the same wavelengths of light used by Secchi 100 years earlier, the astronauts saw incredible details on the sun's surface.
.
.
wavelength radiated by the hydrogen atoms.
We can see sunspots, networks, filaments, all of these things, in great detail.
We all took a four-hour turn at the solar telescope panel.
It's like playing three 88-keyboard pianos at the same time.
'It was a very complicated set of switching and everything.
' It was very intense.
You'd work hard to make sure the sequences read the right way.
Things would come up in real time, like solar flares, so we had to be prepared to catch that also.
Solar flares are planet-sized eruptions of boiling gas, prominences that break free of the sun.
They'd been seen from Earth, but not in such detail and quantity.
Somebody was running it and would call us to take a look.
That happened frequently, when something unusual came up that we could witness, we'd call the other guys up to take a peek.
In nine months, successive Skylab crews took more than 160,000 images, revealing hitherto unknown aspects of the sun.
Their most spectacular discoveries were the coronal mass ejections, outbursts of material on a scale that dwarfed solar flares.
These were the best views yet of the angry sun.
But what causes these convulsions? The answer lies in an invisible side to our sun, and once again, sunspots were the key to its discovery.
Long before the space age, the summit of the San Gabriel mountains was the closest an American could get to space.
In 1903, George Ellery Hale, the son of an engineer, had a dream.
He'd build the world's most advanced solar observatory, high above the town of Pasadena.
Sallie Baliunas is an astrophysicist at the Mount Wilson observatory.
Hale is my personal hero.
He was a great scientist and had instinct about engineering, so he could successfully build the world's largest telescopes.
He raised a lot of money to do these projects.
'As he often said, he made no small plans.
' The route to the top of Mount Wilson wasn't easy.
'This road wasn't built until 1936, 'so all the concrete and steel had to be brought up 'by backpack or mule train on a very steep seven-mile trail.
' The packhorses made 60 trips to transport the telescope alone, but Hale soon had an observatory that was the envy of the world.
His first challenge was to understand the sunspots.
Hale built a spectrograph, which is here beneath this table.
75 feet below is a grating, that disperses the light of the sun into its energy components.
The grating would look like this, and would break the sunlight into its different colours.
In this spectrum are the absorption lines of the gases.
With his unique spectrograph, Hale started analysing the sun's surface.
He could take photographs of sunspots in more detail than anyone had before.
During a routine study of the chemical absorption lines of the sun's surface, he made a breakthrough.
'Looking at the quieter part of the sun, 'he saw ordinary-looking absorption lines.
'Then as the sunspot rolled into the slit, 'the lines began to broaden and split.
' Hale saw the lines split apart and recognised the phenomenon.
Voilà , magnetic fields.
He could see it.
June 1908.
Hale had unravelled one of the sun's greatest mysteries.
Sunspots were caused by magnetic distortion.
These distortions are 4,000 times greater than the Earth's magnetic field.
They suppress the upward surge of gases, cooling the surface by 2000 degrees, and causing the dark spots.
'A sunspot on the surface 'is just a twisted and kinked magnetic field, 'looped out of the surface.
' This magnetogram shows how the surface is speckled with positive and negative lines of magnetic force.
These tortured field lines channel the sun's storms - eruptions of plasma, exploding outwards for thousands of kilometres, before being dragged back into its boiling surface.
'Coronal mass ejections, prominences, 'all features on the sun's surface are magnetic in nature.
' In one of the coldest places on Earth, 15 years before Hale started his investigation into the sun, a Norwegian scientist had drawn his own conclusions about the sun's magnetism.
In a land where you can't see the sun for months, he was convinced you could feel its presence in one of the most beautiful phenomena on Earth.
'It may be strange to see why we're here, far to the north, in the darkness, dealing with the sun.
But here you see the aurora, the Northern Lights.
I really like to see the aurora.
It's beautiful in many colours you don't see anywhere else.
It really lights up the dark days here in wintertime.
'Earlier, it was thought the Northern Lights 'was the souls of dead soldiers fighting.
' (Whistling and humming) Norway is one of the best places to study auroras.
Truls Hansen monitors the radioactivity high in the Earth's atmosphere.
This area of research goes back over a century.
100 years ago, Norway's most famous scientist dedicated his life to the study of atmospheric disturbances.
His name was Doctor Christian Birkeland.
Birkeland was brilliant, but a bit mad.
You might see that from his book.
It contains not only theories about particles and the aurora, but a lot of ideas.
Some right, most wrong.
One of them was Terrela, which we see clearly here.
A vacuum chamber with a small globe, pretending the Earth inside it.
'We can also see Birkeland, controlling the experiment.
' This experiment artificially created the Northern Lights.
To protect his brain from radiation, he always wore a fez.
Birkeland's theories about the origin of auroras stemmed from years of dedicated study.
Auroral activity is particularly energetic after a period of solar activity.
Birkeland wanted to find a mechanism to link the two.
These are the old magnetometers, which have been operating for more than 100 years.
They're still used here and there.
Birkeland used very similar instruments.
Here's a recording of the magnetic field, taken with this instrument.
It starts quiet around noon, and then, here in the evening, you get a magnetic storm, which you see clearly here.
During this period you have a large and very bright aurora.
This is the Birkeland Terella experiment.
He built several, but this is the biggest one, and the last one, I suppose, being made in 1913.
It's a large vacuum chamber with a model of the Earth inside.
Birkeland thought the magnetic storms with the Northern Lights were caused by electrically-charged particles buffeting the Earth's magnetic field.
He believed these particles came from the sun, but his ideas were never taken up.
In 1917, Birkeland committed suicide.
In fact, evidence of the extraordinary reach of the sun had been visiting our skies for millennia.
The dusty comet tails always point away from the sun.
It was assumed that sunlight alone was the cause.
But in 1947, a German physicist, Ludwig Bierman, calculated that something far more substantial had to be pushing the comet tails.
He called it solar corpuscular radiation, and his idea was rejected immediately.
Despite the general derision, physicist Eugene Parker was unable to dismiss Bierman's argument.
'I had a chance to talk to him in Chicago.
' He said if it isn't sunlight, then it must be the solar corpuscular radiation, the emission of particles from the sun that blow the tail away from the sun.
'His revelations made me see he had a fundamental point.
' The physicist Sidney Chapman was very eager to attack Bierman.
He said the sun was 330,000 times more massive than Earth, and that no particle, however small, could escape its enormous gravitational pull.
Regardless of his scorn for the solar wind, Chapman was developing his own idea for how the sun was reaching out to the Earth.
He suggested the corona, though firmly bound to the sun, stretched much farther than is seen during an eclipse.
Eugene Parker met Sidney Chapman in Boulder, Colorado.
I was thinking about what I had learned from Chapman, that the corona extends out through the solar system.
I realised that Chapman and Bierman were mutually exclusive.
The solar corpuscular radiation that affects the comet tails can't penetrate through a static corona, interactions block this.
But I could not see that either one of them was wrong.
Parker worked at the apparent contradiction in the theories, and found that both were right.
'I integrated the equations of motion.
' I found only one solution that fitted the condition of strong rebound at the sun and zero pressure in infinity.
That was the solution providing the supersonic solar wind.
Parker's solar wind was more complex than Bierman's version.
He calculated the corona did have enough thermal energy to escape its gravity and stream off at 500km a second.
But when he went public, Parker himself was ridiculed.
'The referees for my papers were anonymous.
'I was assured they were experts.
'They declared the ideas were absurd.
' Others declared it was false, and published papers showing alternatives, and gave lectures decrying the idea.
My friends said, "It was a great idea, "but great ideas often fall on their face.
" My reaction was, "We'll see what falls on its face.
" Parker waited five years for his theory to be vindicated.
in 1962, the Mariner 2 probe to Venus carried particle detectors designed to discover how empty space was.
The world's first interplanetary probe signalled back that space is awash with a solar wind exceeding Parker's estimates.
'The JPL plasma detector 'showed there was a wind 'of anywhere from 300 to 800km per second.
' The wind was always there and never ceased.
I refused to argue with anybody after that.
Modern telescopes have revealed the complexity of Parker's solar wind.
From the sun's equator particles constantly evaporate into space.
Occasionally, gusts break free of the sun's gravitational and magnetic forces.
These are the flares and coronal mass ejections seen by Skylab.
These electrically-charged hurricanes are ferocious and relentless.
The planets lie in their firing line.
Mercury, closest to the sun, bares the brunt of the solar wind.
Any atmosphere this world may have had has been blown away, leaving its surface bathed in deadly radiation.
Mars is four times further from the sun than Mercury, yet it's thought the solar wind has stripped a third of its original atmosphere, leaving a veil one hundred times thinner than ours.
Venus, our nearest neighbour, has an atmosphere a hundred times thicker than ours.
Modern probes discovered a comet-like tail that stretches back to the Earth's orbit.
The clouds on Venus are also being eroded by the solar wind.
And what of our atmosphere? Earth has a magnetic field that stretches far out into space.
It deflects the solar wind and protects our atmosphere.
A force-field fighting a constant battle with the sun.
The solar wind and the Earth's magnetic field battle together.
The magnetic field is being compressed by the solar wind.
'As this pressure increases, 'and sends the particles through along the magnetic fields 'down to the Earth's polar areas, 'we see them as aurora in the upper atmosphere.
' We live in a region dominated by the solar wind, which extends far out into space.
'The next question is how far out into space it extends, 'as it spreads out farther from the sun.
' What is the full extent of the sun? The first space probes venturing to Jupiter recorded massive radio emissions.
That was the same battle between Jupiter's magnetic field and the solar wind.
As the spacecraft Voyager visited the outer planets, it found the same signature of solar wind buffeting magnetic fields.
When it left Neptune, the solar wind was still there.
Where would it end? Three years beyond Pluto, it detected a mysterious burst of radio energy.
The signals were picked up at the tracking station at Goldstone, California, where Don Gurnett had been keeping in touch with Voyager.
My primary interest now is following the solar wind as it expands out from the sun.
It has to be stopped some place by the interstellar gas.
This boundary we call the heliopause.
The radio burst picked up by Voyager was totally unexpected.
There were no giant planets within three billion kilometres.
We didn't know the signal's origin.
We thought it was coming from Jupiter or Saturn.
Or maybe it was coming from much further away from the sun.
Their search led them back to the heart of the solar system.
We noticed a series of very powerful coronal mass ejections, 'some 400 days before the radio burst.
' Checking through Voyager's log, Don found it had been overtaken by the outburst after 100 days.
300 days later, the solar gust reached a magnetic boundary.
Was this the heliopause, the outer limit of the solar wind? Our model is that this coronal mass ejection produced a plasma pulse coming out from the sun that propagated for 400 days.
We detected it going by Voyager One and Two.
That pulse of plasma eventually reached the heliopause, and caused the radio emission.
The radio burst places the heliopause at four times the distance of Pluto.
This is the extent of the sun.
Even the most distant planets, where the sun's just a bright star, bathe in its evaporating atmosphere.
The planets are bound by our sun's gravity.
They were formed as a by-product of its creation.
There's a more fundamental bond between the planets and the stars.
The very stuff of life is built inside them.
A star's core is the ultimate fusion reactor.
Douglas Gough wants to see it in action.
'My goal is to learn about the structure of the core, 'because the nuclear physics is so interesting.
' The nuclear reactions that change material, that produce new particles that leave the sun, help us understand the physics of elementary matter.
1995 saw the launch of a new era of solar exploration.
A journey that may take us to the heart of a star.
The solar observatory SOHO can view the sun in X-rays, ultra-violet and visible light.
But SOHO doesn't just look.
It listens.
In 1975, when Gough learned the sun's surface rippled like a pond, he instantly saw a way to see to its core.
'I realised this is a way of seeing inside the sun.
' You can't see inside the sun with light, it's opaque.
But this was sound.
You can hear inside it.
By doing so, you could learn the structure of the sun inside.
I found that an amazing concept, that you could get inside a star.
The surface of the sun is heaving.
Every six minutes the entire star breathes in and out.
Its gaseous ocean swells and dips, and a complex pattern of ripples shimmer across its surface.
Clues to the structure within.
'The sun's like a chorus of instruments, 'playing, but not in tune.
' It's cacophonous, which gives much information about the detailed interior.
The sound waves move back and forth, and give tones, like a musical instrument.
SOHO has revealed new surface phenomena.
After a solar flare, seismic quakes spread out for thousands of kilometres.
But there's much more.
'We've learned about the sun's outside' from studying the sound waves from SOHO.
We've learned about the dynamics and the chemical composition.
We want to do something similar in the core.
SOHO has started to strip away the sun's outer layers.
Under its surface, it discovered rivers of plasma, super-heated gases that circle its pole.
Looking like the jet stream on Earth, it seems the sun has weather too.
But deep in the core is that remarkable chemical factory.
'The stars make all the matter that we are made of, 'from hydrogen and helium.
That's what we're made of.
'They're the factories that make material.
'To understand the universe, we need to study the stars.
' Every star has a core.
Almost all stars are generating nuclear energy, transmuting elements from one to another, building up the heavy elements of the universe.
We believe the stars' physics are the same as on Earth.
This physics we must understand more carefully, so we can work out what that implies about the structure of the universe and how it evolves.
In the beginning, the universe contained hydrogen and helium.
For 12 billion years, stars have been transforming them into more complex elements.
Our sun is born from that process.
4.
5 billion years ago, a star on the fringes of our galaxy ended its existence as a supernova.
Its death throes sent the contents of its core into space.
These heated grains of silicon, iron and many other elements careered into a cloud of gas, causing it to collapse.
As the gas and dust mixture went to the cloud's centre, they ignited a nuclear reaction and our sun burst into life.
The remaining debris from the supernova formed the planets.
We are made of star dust, forged in the heart of a star.
In the last 400 years, science has peeled back our sun's layers, to reveal a star, one of the countless engines of creation, which made the planets, which made us.
Our ancestors saw a perfect disc of light.
A god.
Science has revealed an entity more powerful than they could ever have imagined.
Their mission was to observe the sun, free from the Earth's distorting atmosphere.
They witnessed what no one had seen before, a sun more powerful than they had ever imagined.
To our ancestors, the sky was a patchwork of puzzles.
At night, it was brimming with pinpoints of light - stars.
Then there was the sun, whose arrival banished the stars and brought warmth and light.
It was hailed as the giver of life, the first god.
This is the story of mankind's struggle to see behind the glare and glimpse the truth about the sun and how we came to understand its power and its role in the universe.
(Carnival music) In February 1998, the Caribbean island of Guadeloupe geared itself up for a rare celestial event.
For a few minutes, day would become night during a total eclipse of the sun.
This was Francisco Diego's tenth eclipse.
As a boy, he was deeply affected by his first.
It started a lifelong fascination with the sun.
'The sun was perceived as an immaculate' gold disc, perfect.
It was a religious belief.
Everything was perfect in the sky.
The sun was the most perfect circle, with no blemishes or structure.
A perfect, flat, golden disc.
'It was the sun god for many religions.
' The sun remained a symbol of perfection until a 17th-century Florentine called Galileo first pointed a telescope at the sky, and instantly recorded the first scientific milestone.
'Galileo applied the telescope for the first time, 'and discovered the sun wasn't perfect.
'It had sunspots.
'That was a major revolution in philosophy and science.
' Galileo watched the sunspots move across the sun's surface and realised it was spinning.
It was the first of many secrets sunspots would reveal.
Galileo's insight heightened speculation about the true nature of our sun.
But for two centuries, astronomers were frustrated by its blinding disc.
What were sunspots? What other landscapes existed on the sun's surface? What was the source of its power? There were moments, scientists realised, when the sun offers a rare and special opportunity.
Roughly six times every decade, somewhere around the world, the sun passes directly behind the Moon.
If the sun's this big, Earth's a little ball of 3-4mm in diameter and the Moon is even smaller.
It's a quarter of the Earth, 400 times smaller than the sun.
The fantastic coincidence is that the sun is 400 times further away than the Moon from us, so we see both more or less the same size.
(Man ) One minute! For 4 hours, Francisco watched the Moon creep into position.
(Man ) No filters! He came halfway round the world for just four minutes of totality.
But where the sun is concerned, dedication has never been any guarantee of success.
(People shout and cheer) Francisco got just a few moments to glimpse the hidden sun.
We lost it.
No corona.
Like many astronomers before him, Francisco was thwarted as the clouds rolled in to spoil the party.
Douglas Gough is a leading solar scientist.
To see his first total eclipse, he had travelled to Indonesia.
The government had declared it illegal to watch the eclipse, at least for the Indonesians.
They had to watch it on TV or go to the mosque and pray the dragon would spit the sun out.
They believed that was happening.
I was standing on a road, and a little boy came up to me.
I gave him a dark film, to look at the sun.
An old man of 70, the head of the village, came too, and the three of us saw a fantastic eclipse.
A total eclipse reveals the sun's corona, an outer layer normally lost in the glare.
'An eerie feeling, and almost total silence.
'The only thing we heard was the chanting from the mosques.
' This is what early astronomers travelled the world to see.
Within the corona were seemingly burning clouds.
The surface looked smothered in a complex, raging atmosphere.
'You realise, seeing these things, 'the sun's active, not a passive ball of gas.
'It's churning away.
Interesting things are happening.
' Discovering new things is exciting.
That's why explorers explored places no man had been before.
On Earth, there's little left, so we go into the universe.
Seeing the sun, peeling off a layer of mist, of lack of understanding, and seeing how something works, is an amazing experience.
The rarity of a clear eclipse gave scientists few chances to study these prominences.
In the 19th century, Father Angelo Secchi, the Vatican's chief astronomer, caused a revolution in the way we looked at light.
From an observatory above his church, he pioneered a new branch of science - spectroscopy.
His spectroscope split sunlight into its constituent colours, then magnified the light in one region.
It was possible to see the sun's edge, without relying on an eclipse.
Spectroscopy revealed a solar surface of astonishing complexity.
You were no longer dazzled by the sunlight.
You could see the things you can see at the edge of the sun during an eclipse.
Soon astronomers were studying the body of the sun.
The sunspots were Earth-sized tears in the surface.
Like windows on a mysterious interior.
The surface itself bubbled before their eyes.
Soon they were cataloguing the chemicals in the sun.
Dark bands in its spectrum meant hydrogen, calcium, iron.
Astronomers discovered an alien element, unknown on Earth.
They named it after Helios, the Greek sun god.
Helium.
When Secchi turned his spectroscope to the stars, he made his most profound discovery.
He recognised the pattern immediately.
Their chemistry was identical to the sun.
One great mystery of the heavens was resolved.
Our sun was a star.
The sun was a star, and one realised it belonged to the family of stars.
'Scientifically, that's fantastic, 'as we want to know what the universe is like.
'By studying the sun, we study a typical star.
' In the '40s we got our first inkling of how deadly a typical star can be.
As the first rockets rose to the fringes of space, they were scorched with radiation.
Our atmosphere lets heat and light through, but shields us from X-rays, gamma rays and ultra-violet light from the sun.
Soon a man was to brave this deadly radiation, and come face to face with a star.
Alexei Leonov.
'Three, two, one, zero.
' In 1973, a solar laboratory was sent to study the sun directly from space.
But the sun didn't give up its secrets lightly.
'When Skylab was launched, it had a heat shield, 'that was to open up after it got into orbit.
' Sixty seconds into flight, that heat shield popped open.
It's still in the air stream, so the air stream tore the heat shield off, and unlocked both solar wings.
Conrad had been on the Moon when he became crew leader on Skylab.
Their home was no longer protected by an atmosphere, and temperatures started to soar.
They had to find a way of shielding the station from the sun's excesses.
'We got this temporary heat shield rig, 'which we could rig from inside, through an air lock.
' We could push, like an umbrella pole, and mylar sheets popped open like an umbrella.
'Then we could pull it to where it was offset a few inches.
'It did make the temperature go down immediately.
' As the temperatures dropped, the crew went into the observatory.
They had to get used to life in a weightless environment.
At first, nausea prevented all but the most hardy from eating.
That problem quickly passed.
Soon space didn't seem so bad.
Then, with no distorting atmosphere to blur their sights, the most extensive period of solar observation ever began.
'The Skylab flight is very dear to my heart.
' I know a lot of people don't understand that It means more to me than going to the Moon.
Part of that was being able to run the solar telescope and know we were bringing back a tremendous amount of information that nobody had before in great quantities.
When I switch to the two positions called h-alpha, these words stand for hydrogen-alpha, called that because the light here comes from light from hydrogen atoms in the sun's atmosphere Viewing the sun in the same wavelengths of light used by Secchi 100 years earlier, the astronauts saw incredible details on the sun's surface.
.
.
wavelength radiated by the hydrogen atoms.
We can see sunspots, networks, filaments, all of these things, in great detail.
We all took a four-hour turn at the solar telescope panel.
It's like playing three 88-keyboard pianos at the same time.
'It was a very complicated set of switching and everything.
' It was very intense.
You'd work hard to make sure the sequences read the right way.
Things would come up in real time, like solar flares, so we had to be prepared to catch that also.
Solar flares are planet-sized eruptions of boiling gas, prominences that break free of the sun.
They'd been seen from Earth, but not in such detail and quantity.
Somebody was running it and would call us to take a look.
That happened frequently, when something unusual came up that we could witness, we'd call the other guys up to take a peek.
In nine months, successive Skylab crews took more than 160,000 images, revealing hitherto unknown aspects of the sun.
Their most spectacular discoveries were the coronal mass ejections, outbursts of material on a scale that dwarfed solar flares.
These were the best views yet of the angry sun.
But what causes these convulsions? The answer lies in an invisible side to our sun, and once again, sunspots were the key to its discovery.
Long before the space age, the summit of the San Gabriel mountains was the closest an American could get to space.
In 1903, George Ellery Hale, the son of an engineer, had a dream.
He'd build the world's most advanced solar observatory, high above the town of Pasadena.
Sallie Baliunas is an astrophysicist at the Mount Wilson observatory.
Hale is my personal hero.
He was a great scientist and had instinct about engineering, so he could successfully build the world's largest telescopes.
He raised a lot of money to do these projects.
'As he often said, he made no small plans.
' The route to the top of Mount Wilson wasn't easy.
'This road wasn't built until 1936, 'so all the concrete and steel had to be brought up 'by backpack or mule train on a very steep seven-mile trail.
' The packhorses made 60 trips to transport the telescope alone, but Hale soon had an observatory that was the envy of the world.
His first challenge was to understand the sunspots.
Hale built a spectrograph, which is here beneath this table.
75 feet below is a grating, that disperses the light of the sun into its energy components.
The grating would look like this, and would break the sunlight into its different colours.
In this spectrum are the absorption lines of the gases.
With his unique spectrograph, Hale started analysing the sun's surface.
He could take photographs of sunspots in more detail than anyone had before.
During a routine study of the chemical absorption lines of the sun's surface, he made a breakthrough.
'Looking at the quieter part of the sun, 'he saw ordinary-looking absorption lines.
'Then as the sunspot rolled into the slit, 'the lines began to broaden and split.
' Hale saw the lines split apart and recognised the phenomenon.
Voilà , magnetic fields.
He could see it.
June 1908.
Hale had unravelled one of the sun's greatest mysteries.
Sunspots were caused by magnetic distortion.
These distortions are 4,000 times greater than the Earth's magnetic field.
They suppress the upward surge of gases, cooling the surface by 2000 degrees, and causing the dark spots.
'A sunspot on the surface 'is just a twisted and kinked magnetic field, 'looped out of the surface.
' This magnetogram shows how the surface is speckled with positive and negative lines of magnetic force.
These tortured field lines channel the sun's storms - eruptions of plasma, exploding outwards for thousands of kilometres, before being dragged back into its boiling surface.
'Coronal mass ejections, prominences, 'all features on the sun's surface are magnetic in nature.
' In one of the coldest places on Earth, 15 years before Hale started his investigation into the sun, a Norwegian scientist had drawn his own conclusions about the sun's magnetism.
In a land where you can't see the sun for months, he was convinced you could feel its presence in one of the most beautiful phenomena on Earth.
'It may be strange to see why we're here, far to the north, in the darkness, dealing with the sun.
But here you see the aurora, the Northern Lights.
I really like to see the aurora.
It's beautiful in many colours you don't see anywhere else.
It really lights up the dark days here in wintertime.
'Earlier, it was thought the Northern Lights 'was the souls of dead soldiers fighting.
' (Whistling and humming) Norway is one of the best places to study auroras.
Truls Hansen monitors the radioactivity high in the Earth's atmosphere.
This area of research goes back over a century.
100 years ago, Norway's most famous scientist dedicated his life to the study of atmospheric disturbances.
His name was Doctor Christian Birkeland.
Birkeland was brilliant, but a bit mad.
You might see that from his book.
It contains not only theories about particles and the aurora, but a lot of ideas.
Some right, most wrong.
One of them was Terrela, which we see clearly here.
A vacuum chamber with a small globe, pretending the Earth inside it.
'We can also see Birkeland, controlling the experiment.
' This experiment artificially created the Northern Lights.
To protect his brain from radiation, he always wore a fez.
Birkeland's theories about the origin of auroras stemmed from years of dedicated study.
Auroral activity is particularly energetic after a period of solar activity.
Birkeland wanted to find a mechanism to link the two.
These are the old magnetometers, which have been operating for more than 100 years.
They're still used here and there.
Birkeland used very similar instruments.
Here's a recording of the magnetic field, taken with this instrument.
It starts quiet around noon, and then, here in the evening, you get a magnetic storm, which you see clearly here.
During this period you have a large and very bright aurora.
This is the Birkeland Terella experiment.
He built several, but this is the biggest one, and the last one, I suppose, being made in 1913.
It's a large vacuum chamber with a model of the Earth inside.
Birkeland thought the magnetic storms with the Northern Lights were caused by electrically-charged particles buffeting the Earth's magnetic field.
He believed these particles came from the sun, but his ideas were never taken up.
In 1917, Birkeland committed suicide.
In fact, evidence of the extraordinary reach of the sun had been visiting our skies for millennia.
The dusty comet tails always point away from the sun.
It was assumed that sunlight alone was the cause.
But in 1947, a German physicist, Ludwig Bierman, calculated that something far more substantial had to be pushing the comet tails.
He called it solar corpuscular radiation, and his idea was rejected immediately.
Despite the general derision, physicist Eugene Parker was unable to dismiss Bierman's argument.
'I had a chance to talk to him in Chicago.
' He said if it isn't sunlight, then it must be the solar corpuscular radiation, the emission of particles from the sun that blow the tail away from the sun.
'His revelations made me see he had a fundamental point.
' The physicist Sidney Chapman was very eager to attack Bierman.
He said the sun was 330,000 times more massive than Earth, and that no particle, however small, could escape its enormous gravitational pull.
Regardless of his scorn for the solar wind, Chapman was developing his own idea for how the sun was reaching out to the Earth.
He suggested the corona, though firmly bound to the sun, stretched much farther than is seen during an eclipse.
Eugene Parker met Sidney Chapman in Boulder, Colorado.
I was thinking about what I had learned from Chapman, that the corona extends out through the solar system.
I realised that Chapman and Bierman were mutually exclusive.
The solar corpuscular radiation that affects the comet tails can't penetrate through a static corona, interactions block this.
But I could not see that either one of them was wrong.
Parker worked at the apparent contradiction in the theories, and found that both were right.
'I integrated the equations of motion.
' I found only one solution that fitted the condition of strong rebound at the sun and zero pressure in infinity.
That was the solution providing the supersonic solar wind.
Parker's solar wind was more complex than Bierman's version.
He calculated the corona did have enough thermal energy to escape its gravity and stream off at 500km a second.
But when he went public, Parker himself was ridiculed.
'The referees for my papers were anonymous.
'I was assured they were experts.
'They declared the ideas were absurd.
' Others declared it was false, and published papers showing alternatives, and gave lectures decrying the idea.
My friends said, "It was a great idea, "but great ideas often fall on their face.
" My reaction was, "We'll see what falls on its face.
" Parker waited five years for his theory to be vindicated.
in 1962, the Mariner 2 probe to Venus carried particle detectors designed to discover how empty space was.
The world's first interplanetary probe signalled back that space is awash with a solar wind exceeding Parker's estimates.
'The JPL plasma detector 'showed there was a wind 'of anywhere from 300 to 800km per second.
' The wind was always there and never ceased.
I refused to argue with anybody after that.
Modern telescopes have revealed the complexity of Parker's solar wind.
From the sun's equator particles constantly evaporate into space.
Occasionally, gusts break free of the sun's gravitational and magnetic forces.
These are the flares and coronal mass ejections seen by Skylab.
These electrically-charged hurricanes are ferocious and relentless.
The planets lie in their firing line.
Mercury, closest to the sun, bares the brunt of the solar wind.
Any atmosphere this world may have had has been blown away, leaving its surface bathed in deadly radiation.
Mars is four times further from the sun than Mercury, yet it's thought the solar wind has stripped a third of its original atmosphere, leaving a veil one hundred times thinner than ours.
Venus, our nearest neighbour, has an atmosphere a hundred times thicker than ours.
Modern probes discovered a comet-like tail that stretches back to the Earth's orbit.
The clouds on Venus are also being eroded by the solar wind.
And what of our atmosphere? Earth has a magnetic field that stretches far out into space.
It deflects the solar wind and protects our atmosphere.
A force-field fighting a constant battle with the sun.
The solar wind and the Earth's magnetic field battle together.
The magnetic field is being compressed by the solar wind.
'As this pressure increases, 'and sends the particles through along the magnetic fields 'down to the Earth's polar areas, 'we see them as aurora in the upper atmosphere.
' We live in a region dominated by the solar wind, which extends far out into space.
'The next question is how far out into space it extends, 'as it spreads out farther from the sun.
' What is the full extent of the sun? The first space probes venturing to Jupiter recorded massive radio emissions.
That was the same battle between Jupiter's magnetic field and the solar wind.
As the spacecraft Voyager visited the outer planets, it found the same signature of solar wind buffeting magnetic fields.
When it left Neptune, the solar wind was still there.
Where would it end? Three years beyond Pluto, it detected a mysterious burst of radio energy.
The signals were picked up at the tracking station at Goldstone, California, where Don Gurnett had been keeping in touch with Voyager.
My primary interest now is following the solar wind as it expands out from the sun.
It has to be stopped some place by the interstellar gas.
This boundary we call the heliopause.
The radio burst picked up by Voyager was totally unexpected.
There were no giant planets within three billion kilometres.
We didn't know the signal's origin.
We thought it was coming from Jupiter or Saturn.
Or maybe it was coming from much further away from the sun.
Their search led them back to the heart of the solar system.
We noticed a series of very powerful coronal mass ejections, 'some 400 days before the radio burst.
' Checking through Voyager's log, Don found it had been overtaken by the outburst after 100 days.
300 days later, the solar gust reached a magnetic boundary.
Was this the heliopause, the outer limit of the solar wind? Our model is that this coronal mass ejection produced a plasma pulse coming out from the sun that propagated for 400 days.
We detected it going by Voyager One and Two.
That pulse of plasma eventually reached the heliopause, and caused the radio emission.
The radio burst places the heliopause at four times the distance of Pluto.
This is the extent of the sun.
Even the most distant planets, where the sun's just a bright star, bathe in its evaporating atmosphere.
The planets are bound by our sun's gravity.
They were formed as a by-product of its creation.
There's a more fundamental bond between the planets and the stars.
The very stuff of life is built inside them.
A star's core is the ultimate fusion reactor.
Douglas Gough wants to see it in action.
'My goal is to learn about the structure of the core, 'because the nuclear physics is so interesting.
' The nuclear reactions that change material, that produce new particles that leave the sun, help us understand the physics of elementary matter.
1995 saw the launch of a new era of solar exploration.
A journey that may take us to the heart of a star.
The solar observatory SOHO can view the sun in X-rays, ultra-violet and visible light.
But SOHO doesn't just look.
It listens.
In 1975, when Gough learned the sun's surface rippled like a pond, he instantly saw a way to see to its core.
'I realised this is a way of seeing inside the sun.
' You can't see inside the sun with light, it's opaque.
But this was sound.
You can hear inside it.
By doing so, you could learn the structure of the sun inside.
I found that an amazing concept, that you could get inside a star.
The surface of the sun is heaving.
Every six minutes the entire star breathes in and out.
Its gaseous ocean swells and dips, and a complex pattern of ripples shimmer across its surface.
Clues to the structure within.
'The sun's like a chorus of instruments, 'playing, but not in tune.
' It's cacophonous, which gives much information about the detailed interior.
The sound waves move back and forth, and give tones, like a musical instrument.
SOHO has revealed new surface phenomena.
After a solar flare, seismic quakes spread out for thousands of kilometres.
But there's much more.
'We've learned about the sun's outside' from studying the sound waves from SOHO.
We've learned about the dynamics and the chemical composition.
We want to do something similar in the core.
SOHO has started to strip away the sun's outer layers.
Under its surface, it discovered rivers of plasma, super-heated gases that circle its pole.
Looking like the jet stream on Earth, it seems the sun has weather too.
But deep in the core is that remarkable chemical factory.
'The stars make all the matter that we are made of, 'from hydrogen and helium.
That's what we're made of.
'They're the factories that make material.
'To understand the universe, we need to study the stars.
' Every star has a core.
Almost all stars are generating nuclear energy, transmuting elements from one to another, building up the heavy elements of the universe.
We believe the stars' physics are the same as on Earth.
This physics we must understand more carefully, so we can work out what that implies about the structure of the universe and how it evolves.
In the beginning, the universe contained hydrogen and helium.
For 12 billion years, stars have been transforming them into more complex elements.
Our sun is born from that process.
4.
5 billion years ago, a star on the fringes of our galaxy ended its existence as a supernova.
Its death throes sent the contents of its core into space.
These heated grains of silicon, iron and many other elements careered into a cloud of gas, causing it to collapse.
As the gas and dust mixture went to the cloud's centre, they ignited a nuclear reaction and our sun burst into life.
The remaining debris from the supernova formed the planets.
We are made of star dust, forged in the heart of a star.
In the last 400 years, science has peeled back our sun's layers, to reveal a star, one of the countless engines of creation, which made the planets, which made us.
Our ancestors saw a perfect disc of light.
A god.
Science has revealed an entity more powerful than they could ever have imagined.