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BBC The Planets Star

about the sun and how we came to understand the scope of its power and its role in the universe 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 human being 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, the yellow sphere 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. In February 1998, the Caribbean island of Guadeloupe geared itself up for a rare celestial event. For a few brief minutes, day would become night during a total eclipse of the sun. This was Francisco Diego's tenth eclipse. As a young boy in Mexico, 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. He was perfection; he was a religious belief because everything was perfect in the sky. And the sun was the most perfect circle in the sky, with no blemishes, no structure. Just a perfect flat disc, golden disc. And it was the sun god for many, many religions in the world. 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. What Galileo did was apply the telescope for the first time, and discover that the sun was not perfect, that the sun had sunspots. And that was a major revolution in philosophy and, of course, in science. Galileo watched the sunspots move across the surface of the sun... and realized it was spinning. It was to be the first of many secrets that sunspots would reveal. Galileo's insight heightened speculation about the true nature of our sun. But for two centuries, the curious 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 came to realize, 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 was this big, the Earth will be a little ball of about 3 or 4 mm in diameter and the Moon is even smaller than that. The Moon is a quarter of the size of the Earth, so the Moon is 400 times smaller than the sun. But the fantastic coincidence is that the sun is 400 times farther away than the Moon from us, so we see both of them by coincidence more or less the same size. One minute! For 4 hours, Francisco watched the Moon creep into position. 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. In the end, 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 Indonesian government had declared it to be illegal to watch the eclipse, at least for the Indonesians. They had either to watch it on TV or to go to the mosque and pray for the dragon to spit the sun out again. Which is what they believed was taking place. I was standing at the end of a road on my own, and a little boy came up to me, he'd been watching me, about 3 years old, and I gave him some dark film, to look at the sun through. And an old man of about 70, who turned out the head of the village, came too, and the three of us saw this fantastic eclipse. A total eclipse reveals the sun's corona, an outer layer normally lost in the glare. A very eerie feeling and almost total silence the birds stop singing. The only thing we could hear in the distance was the chanting from the mosques. This is what early astronomers travelled the world to see. Within the corona were what looked like burning clouds? It seemed that the surface of the sun was smothered in a complex, raging atmosphere. But you realize, when you see these things moving, that the sun is active, it's not just a quiet passive ball of gas, but it's churning away. Interesting things are happening. Seeing anything for the first time is exciting. That's why explorers on Earth would explore parts of the Earth where no man had been before. There's very little left of the Earth now to do that, so we go elsewhere the universe. Seeing the sun, peeling off a layer of mist, a layer of lack of understanding, and suddenly seeing how something works, is an amazing experience when you see this for the first time. But the rarity of a clear eclipse gave scientists few chances to study these strange prominences. Then in the middle of the 19th century, Father Angelo Secchi, the Vatican's chief astronomer, found himself at the forefront of a revolution in the way we looked at light. From an observatory above his church in Rome, he pioneered a new branch of science called spectroscopy. Secchi's spectroscope split sunlight into its constituent colors, then magnified the light in just one region. Suddenly it was possible to see the edge of the sun, without relying on an eclipse. Spectroscopy revealed a solar surface of astonishing complexity. What had happen is that you were no longer dazzled by most of the light from the sun. You could see something else; you could see the kinds of things that you can see at the edge of the sun during an eclipse when you're no longer dazzled by the light from the sun. Soon astronomers were studying not just the edges, but the body of the sun. Galileo's sunspots were revealed as 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 present in the sun. Dark bands in its spectrum revealed the presence of hydrogen, calcium, iron. And astronomers discovered an alien element, completely unknown on Earth. They named it after Helios, the Greek sun god. Helium. But it was when Father Secchi turned his spectroscope to the stars, that he made his most profound discovery. He recognized the pattern immediately. Their chemistry was all but identical to the sun. One great mystery of the heavens had been resolved. Our sun was a star. The sun was one of those stars, and so now, for the first time, one realized that the sun was a member of the family of stars. But from the scientific point of view, that's fantastic, because we want to know what most of the universe is like. And so by studying the sun, we can study a typical star. It wasn't until the 1940s that 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 allows heat and light to pass through, but shields us from X-rays, gamma rays and ultra-violet light that come from the sun. Soon a man was to brave this deadly radiation, and come face to face with a star. Alexei Leonov. 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 wrapped around it that was to open up after it got into orbit. And what happened sixty seconds into the flight, that heat shield popped open. And, of course, it's still in the air stream. And so the air stream tore the heat shield off, and when it did that, it unlocked both solar wings. Commander Pete Conrad had already walked on the Moon when he was chosen to lead the first crew on Skylab. But their home was no longer protected by an atmosphere, and inside temperatures started to soar. Their first job was to find some way of shielding the damaged station from the worst of the sun's excesses. Right away on Day 1 we went in and got this temporary heat shield rig, which we were able to rig from inside, we were able to put it out to one of the air locks. We were able to push, just like an umbrella pole, and mylar sheets that then popped open like an umbrella. And then we were able to pull it back in to where it was just offset by a few inches off the side. And it did take care of the heating problem - temperature begin go down immediately. As the temperatures dropped to something survivable, the crew made their way into the observatory. Their next task was to get to grips with life in a weightless environment. Initially, nausea prevented all but the hardiest from eating. But the problem soon passed. And within a few days space didn't seem such a bad place after all. The Skylab flight is very near dear to my heart. I know a lot of people don't understand that... it probably means more to me than going to the Moon, because 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 any great quantities. And to begin with, when I switch to the two positions called h-alpha, these words stand for hydrogen-alpha, and they are called hydrogen because the light we see comes from light radiated by hydrogen atoms in the sun's atmosphere... Viewing the sun in the same wavelengths of light used by Secchi more than 100 years earlier, the Skylab astronauts saw incredible details on the sun's surface. ..Wavelength radiated by the hydrogen atoms. For example, we can see sunspots, we can see networks, and we can see filaments, all of these things on the sun, in great detail. Each one of us took a four-hour turn at the solar telescope panel. Now I always related that like playing three 88-keyboard pianos at the same time. It was a very complicated set of switching and everything. It was very involved and very intense. You'd work real hard during that time frame making sure those sequences read the right way, and then things would come up in real time, like solar flare all of a sudden there, something in, so we had to be prepared to catch that also. Solar flares are planet-sized eruptions of boiling gas, prominences that somehow break free of the sun. They had been seen from Earth, but never in such detail and quantity. Somebody else was running it, they might call us and we could go up and take a look also, so that happened quite frequently, when something really unusual came up that we could witness, while we would call the other guys up to let them 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 dawn of the space age, the summit of the San Gabriel Mountains was as close as it was possible for an American to get to space. In 1962, the Mariner 2 probe to Venus carried particle detectors designed to discover how empty space really was. The world's first interplanetary probe signaled back that space is awash with a solar wind exceeding even Eugene Parker's estimates. The JPL plasma detector simply showed there was a wind of anywhere from 300 to 800 km per second. The wind was always there and never ceased. And that was it. I mean I refused to argue with anybody after that. Modern telescopes have revealed the complexity of Parker's solar wind. From the sun's equator a constant stream of particles evaporates into space. Occasionally, violent gusts break free of the sun's gravitational and magnetic forces. These are the flares and coronal mass ejections first witnessed by Skylab. These electrically-charged hurricanes are ferocious and relentless. And the planets lie in their firing line. Mercury, the closest planet to the sun, bares the full brunt of the solar wind. Any atmosphere that this moon-like world may once have had has long been blown away, leaving its surface bathed in deadly radiation.


  Star about the sun and how we came to understand the scope of its power and its role in the universe
 
Every six minutes the entire star breathes in and out
Every six minutes the entire star breathes in and out
  The stars generate stuff; they make all the matter that we are made of, from hydrogen and helium
The stars generate stuff; they make all the matter that we are made of, from hydrogen and helium
  Earth has a magnetic field that stretches far out into space
Earth has a magnetic field that stretches far out into space
  The most extensive period of solar observation in history
The most extensive period of solar observation in history
 
Mars is larger than Mercury and four times further from the sun, and yet even here it is thought that the solar wind has stripped away up to a third of its original atmosphere, leaving a veil one hundred times thinner than our own. Venus, our nearest neighbor, has an atmosphere one hundred times thicker than ours. Modern space probes have discovered a comet-like tail that stretches back to the orbit of the Earth. The clouds on Venus are also being eroded by the solar wind. This field deflects the solar wind and protects our atmosphere from erosion. A force-field fighting a constant battle with the sun. As the solar wind and the Earth's magnetic field is steadily battling against each other magnetic field is being compressed by the solar wind. And as this pressure increases, and sends the particles through along the magnetic fields and down to the polar areas of the Earth, and we see them as light, as aurora in the upper atmosphere. It's clear that we live in a region dominated by the solar wind, which extends far out into space, far beyond the outer planets. The next question is "How far out into space does this solar wind extend?" as it spreads out going farther from the sun. What is the full extent of the sun? As the first space probes ventured to Jupiter they recorded massive radio emissions. The noise was being generated by the same battle between Jupiter's magnetic field and the solar wind. As the spacecraft Voyager visited all the outer planets, it picked up the same tell tale signature of solar wind buffeting magnetic fields. When it left Neptune, it was still accompanied by the solar wind. 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. Well, my primary interest these days is to follow the solar wind as it expands out from the sun. We know that it has to be stopped some place by the interstellar gas. And this boundary we call the heliopause. The radio burst picked up by Voyager was completely unexpected. There were no giant planets within three billion kilometers. We did not at first really know for sure the origin of the signal. We thought it might be coming from planets such as Jupiter or Saturn. It also occurred to us that it may be coming from much further away from the sun. Their search led them back to the heart of the solar system. We noticed that there was a series of extremely powerful coronal mass ejections, some 400 days before the radio burst. Checking back through Voyager's log, Don Gurnett found it had been overtaken by the outburst after 100 days. 300 days later, the solar gust reached some kind of magnetic boundary. Was this the heliopause, the outer limit of the solar wind? So our basic model is that this coronal mass ejection produced a pulse of plasma that came out from the sun and propagated for 400 days. We detected it going by Voyager 1 and Voyager 2.
And 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 appears as little more than a bright star, bathe in its evaporating atmosphere. The planets are bound by the gravity of our sun. They were formed as a by-product of its creation. But there's a more fundamental bond between the planets and the stars. The very stuff of life is built inside them. A core of a star is the ultimate fusion reactor. Douglas Gough wants to see it in action. My ultimate goal is namely 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, understanding that helps us to understand the basic physics of elementary matter. 1995 saw the launch of a new era of solar exploration. The start of a journey that may take us to the heart of the 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 Douglas Gough learned that the sun's surface rippled like a pond, he instantly saw a way to see into its core. What I realized is that this is a way of seeing inside the sun. You can't see inside the sun with a light because it's opaque. But this was really sound you can hear inside the sun. And by hearing inside the sun, you could learn what the structure of the sun is inside. And this was an amazing concept for me, that you could actually get inside the 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 is like a chorus of people, of instruments, playing, but not in tune. And they were very different as cacophonous, which gives us lots of information about the detailed interior. The sound waves move back and forth inside the sun, and give tones, just like the tones of a musical instrument. Already SOHO has revealed new surface phenomena. In the aftermath of the solar flare, seismic quakes spread out for thousands of kilometers. But there's much more. We've learned the great deal about the outside of the sun from studying the sound waves, the seismic waves from SOHO. We've learned about the dynamics, now we want to do something similar in the very core. SOHO has already started to strip away the outer layers of the sun. Beneath its surface, it has 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. But they make this heavy stuff that we are made of. They're the factories that make material. So 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, the whole building blocks of the universe. We believe the physics in those stars is the same as the physics on Earth. This physics we need to understand more carefully so that under extreme conditions, we can work out what that physics implies, on the very large scale, what it implies about the structure of the universe and how the whole universe evolves. In the beginning, the universe contained just hydrogen and helium. For 12 billion years, stars have been transforming these simple gases into more complex elements. Our sun is born from that process. 4.5 billion years ago, a massive star on the fringes of our galaxy ended its existence as a supernova. Its death throes sent the contents of its core spraying upwards into space. These superheated grains of silicon, iron and many other elements careered into a neighboring cloud of gas, causing it to collapse. As the mixture of gas and dust gravitated towards the centre of the cloud, they ignited a nuclear reaction and our sun burst into life. Around it, the remaining debris from the supernova accreted to form the planets. We are made of star dust, forged in the heart of a star.