 Hi, my name is Helmut Gergen. I'm an astrophysicist at the Richard School of Astronomy and Astrophysics, which is part of the Australian National University. In my profession, people often ask me the question, what do astronomers do and what is all good for? I would like to argue that astronomy has the single largest impact on the development of science, human society, and culture over the last 10,000 years. Let me give you some examples. In the 9th to the 10th Dynasty, by 2000 BC, in the ancient Egyptian culture, they started to use constellations of stars to keep track of time. They subdivided the stars, which could rise consecutively over the horizon in 36 distinct groups, which they called vacu or decans. I show you here on the right side. On the left side here, I show you vacu's, which are drawn on the ceiling of the burial chamber of Sete I. Over time, 12 of these vacu's could be observed during a short summer night. And this concept of using stars as a natural clock led to the division of a day into 24 intervals or hours over the time. The most important event in the Egyptian year was the first brief appearance of the Bright Star series in the eastern sky just before the sun rises. Coincidentally, this heliocallic rising of series at the end of June heralded the annual flooding of the River Nile. The Nile is the only significant source of water in the desert region. And the flooding meant for the culture and the civilization there water and fertile soil for cultivating crop. Were it not for the Nile, ancient Egyptian culture civilization could not have been developed. Let me show you briefly how this heliocallic rising of series appears in the night sky. What I show you here in this movie is you're looking to the east and we see just before the sun rises how series here on the right side will briefly appear. We have the sun rising here on the left just coming up now. And series just over here is briefly visible before it gets overpowered the light from series by the bright sun. In other cultures, like the Mayans civilization in Mesoamerica, they use the large monuments that related to the solar calendar. For instance, like this temple of Kukulkar. This huge step pyramid had four staircases and with each 91 steps going up to the top. Now four times 91 gives you 364 plus the top 365. So these different steps reflected every day throughout a solar year. Breasts could use this building to predict the rain cycle for planting crops, like using the natural sky of the appearance of series used by the Egyptians. So they could predict the weather and make weather forecasts and could tell the farmers when to plant the crop, the corn that was the only cereal they used to domesticate. Measuring the angle of separations between objects in the sky required basic instruments like a compass and ruler. And they were combined together with the mathematical concept of trigonometry to track the motions of the stars and the plants. The trigonometry concepts were introduced by the Sumerian and Babylonian and Nubian astronomers five to 7,000 years ago. The mathematical was then fully developed by the Greek astronomer Hipparchos around 150 BC. We all know trigonometry from school and we are aware today how many that they were actually used in many, many fields in science and physics and chemistry. For instance, navigation, architecture, engineering, acoustics, computer graphics, computer games, for instance, or medical imaging. So another very important contribution of astronomers to science and human society. One of the fundamental quest in astronomy is actually to find an accurate model of the universe. How does the universe works, from a physical point of view. The geometrical model proposed by the Greek philosopher Aristotle in 350 BC and mathematically refined by Ptolemy in his armadges book 150 AD was accepted for almost 2,000 years to be the best description of the universe. This is shown here in this drawing what it essentially has as the name suggests. The geocentric model has the Earth in the center and other objects like the planets, like the moon, like the sun, are actually orbiting around the Earth. A serious competition to this model came up with the introduction of the heliocentric model proposed by Copernicus in his famous book The Revolutionibus Orbium Colestium in 1543. This model here, which is shown here on the right, in contrast to the geocentric model, had the sun in the center. And the planets are orbiting around the sun and the moon is orbiting around the Earth. The reason for introducing this model was primarily because the model offered a very good description of the motion of the planets. And most importantly, it was much less complicated than the geocentric model. However, that was just a separate possible solution for describing the universe. There were no observations that could help at that time that could help to discriminate between these two models. It took another 47 years to settle the case. It was Galileo Galilei in 1610 who made use of the first time of a telescope, which is shown up here, to accurately follow the motions of the planets and to make extra observations. That was the first time that actually there was an instrument used to observe the night sky. And it had immediate impact on our understanding how the universe works. For instance, Galileo found the four largest moons of Jupiter. As a consequence, he realized that all the heavenly bodies are actually circling around the Earth. This is a drawing from his log book, and it shows Jupiter here as this star-like object, and then four little dots going around. And as a function of time, over a couple of months, he realized that all these little dots, which are the four Galilei moons nowadays, are actually moving around back and forth. Sometimes you have three on one side and one on the other, or you have four on one side. So this showed that these moons are not opening around Earth, like predicted in the geocentric model, but they're actually opening around Jupiter. What he also observed was the spots on the sun. He immediately realized here that the divine object is not as perfect as it looked initially. And using the sunspots that going across the sun's surface because of the rotation, he realized, OK, this body is actually rotating. It's not stationary in space. A third important observation was the different phases of Venus. And they were not conformed, that's shown here. They were not conformed with the geocentric world model, which gave another prediction how the Venus phases would look like. So all these observations with the help of one single instrument helped to improve our understanding, which is actually the right cosmological model. It was actually the geocentric model. We know that Galileo was forced by the Inquisition to abdure, to curse, and to test what he saw. But what was the important key here is that he had the tools to, and he can offer the tools to everybody to actually test his claim by simply verifying it, looking through the telescopes. Now, one central part, one central object that plays a very important role for us humans is, of course, our sun. And as you will know, our sun is actually a star. The only reason why we see this star so close, and there's a huge bright disc during the day, is simply because it's very, very close, whereas all the other stars are much further away and appear in the night sky as little dots, bright dots. Now, astronomers had to think about very carefully what is actually the sun made out of. What is it? And it took almost until the earliest 20th century to find the right answer. When you look at the movie, like here provided by the Soho satellite, you can already guess what the sun is made out of, thanks to these very high-resolution images. You can see, first of all, it's rotating, and you have prominent explosions on the surface of the sun, which tells us here immediately that it looks like the sun is made out of gas. And these stars, like our sun, our gigantic power stations, which radiates all the energy out, and that's why we have here, on Earth, light and warm temperatures. When you look at the sun, like this image here, shown again, an image from the Soho satellite, the reason why this sun looks like, as it does in a spherical, beautiful gas cloud, is there is a balance between the gravitational force that pushes the mass of the sun inwards and the high pressure from the gas, the radiation pressure from the gas that pushes outwards. So a star, like our sun, is essentially just a balanced gas cloud, a balance between the gravitational force and the pressure from the hot gas. Now, what is happening in this very, very special environment? In fact, the whole star, our sun, is made out of primarily two elements. About 71% is hydrogen and 27% is helium. And in huge quantities, 2,000 million, million, million, million tons of these two elements make up the entire star. Because of this high mass, this large mass, and high pressures that are produced in the center, we have a central temperature of the order of 15.7 million degrees. And every second in the sun, about 700 million tons of the hydrogen gas is converted to 695 million tons of helium and about 5,500 tons of energy. That corresponds to an energy output of about 4 times 10 to the 26 watts, or equivalent of about 2 billion power stations on Earth. It's a huge amount of energy that gets produced every second out of our sun. Now, in this process of converting hydrogen into helium, there are other steps. And in this many, many steps, different elements, chemical elements are synthesized by these nuclear reactions, for instance, carbon, nitrogen, oxygen, magnesium, and silicon. All these different elements are synthesized over the course of the lifetime of the star. Now, this is a very interesting concept. And it might be useful to produce energy here on Earth. And this is actually a real concept at the moment that is explored by an international consortium of different countries like China, Europe, India, Japan, Korea, Russia, and the US. And it's called the International Thermonuclear Experimental Reactor, or E2. It's essentially a man-made sun, a fusion reactor where we exactly try to mimic these very hot, very dense environments and generate the energy in a way the sun does it at the moment. E2 is an experimental reactor, as the name says. I show you here on the left a model sketch. Here you have this, find the primary building here. And inside in the building, you have a torus. This is to scale a human. And that torus, because of these high temperatures that you have, you want to keep the plasma, this very hot gas, away from any material. And to do that, you generate a large magnetic field. And this is what you see here, all these different tiles, metal tiles, where that can help that produces the magnetic field. So once it's operational, you have a plasma ring, a ring of plasma, that rotates around in this torus and gets heated up to these very high temperatures. And the hope is that with this experimental reactor, we can put in about 50 million watts of energy, and we get about a factor of 10 more out of it. So about 500 megawatts as the output. If the whole technique, once the whole technique is established, there is already a next generation of experimental reactor in planning, the so-called demo reactor, where the physicists put in about 80 million watts and hope to get out about 2 billion watts, 2 million watts. And if that all goes according to expectations, and the success is there, we know how the physicists know how to produce this energy in a safe way, then the proton should be at the time of around 2050. This new reactor should be the first commercial nuclear fusion reactor power plant that we have in the world. So in other words, we learned from the sun how the sun produces its energy. And we're using this technique today on Earth to try to generate the same way energy as the sun does. So thanks to the astronomers and physicists and mathematicians who established these processes, understood the processes that happened in the sun, we are now able to reproduce that in fusion power stations. Now you're probably wondering, the star, our sun, is made out of hydrogen helium. And it fuses these elements into higher elements. And they must be most likely an end, because once it's all the fuel is used up, and there will be no more left. And immediately, what would happen is this radiation pressure that pushes it outwards is no longer there, so the gravitation force will take over and it will lead to the end of the star. So somehow there must be a life cycle to our sun and to the stars. Astronomers are not in a situation to actually can observe the life cycle of stars directly, but they can take photos of different steps, different epochs of the life cycle to understand what is going on, how stars form, and how they evolve, and how they die at the end. It's similar like taking photos of a crowd of people and then having children, teenagers, and other age as covered by this photo, and then you can make a sequence together and try to understand the life cycle of humans. So astronomers, for that purpose, use, for instance, the Hubble Space Telescope. We're looking into the region where most of the stars are in the sky, which is this white strip in the sky from the Milky Way, the band of the Milky Way. Let's zoom in and have a look what we can find in the Milky Way. For instance, this here, this is a huge gas cloud. Oh, we know already, hydrogen helium is actually two types of gas. So that could be the region where actually stars are formed. And indeed, it's the case. We see here actually the cocoon where stars are formed. Similar to humans, astronomers cannot directly see what's going on in the optical here, but we have to wait for a while to see what comes out of this. Now, by the 100 million years it requires for astronomers to see how the very young bright stars right in the middle of these cocoons of gas are able to, with their radiation, are able to remove the gas and make them self-visible. So the radiation pushes out the left over gas, and we see right in the middle of these cocoons very young bright stars. The cellar winds from these stars remove the left over gas. Now, there's 100 million years. We are astronomers dealing with very large numbers, and sometimes we're confusing, but the good news is here that we have quite a good analogy to humans. Human life evolves just a factor of about 100 million slower than, sorry, human life evolves just a factor of 100 million faster than the life of a star. So we simply can cancel eight of the digits here to have a comparison with a human, which is Shani, a baby, on the lower right side. So let's see what happens with a star, a young star group, as you can see here, what is happening over the time. After about 400 million years, most of the gas is removed, as you can see here in this beautiful consolation of the bledadies, and we see the very blue, very, very young bright stars that are shining with the light. But that's, again, comparable to humans by simply canceling the eight digits and get an age of four. So very young stars that we see here in the bledadies. Now, the good news is that the life of stars is relatively boring. The good news is for us because our sun is so calm, our star is so calm, for billions of years. And that gives us a very, gives an opportunity for prosperous times for planets to form and to life develop. Our sun, for instance, is currently about 4.5 billion years old. So right in the middle, right in the middle-aged type of star that we are having, where we're orbiting around with our Earth. You might ask the question, how long does it take for our sun until it's the end, until it consumes up all its energy? And the answer is about 9 billion years. With stars, the final stages, the final phase of their life is very, very prominent, as I show you here on this figure. That what I show you here is a field of stars, a gas cloud where young new stars are formed at the moment. But the arrow here indicates a very unsuspicious star that turned from one second to the other, essentially, died from one second to the other, and turned into a very, very bright object, as we can see it right here. Now, astronomers, because of this phenomena, thought initially that there is nothing there, but then suddenly a new bright star is up in the sky. And they called these events Norway or supernovae for a new type of stars that they could observe. In fact, it was realized, as a physicist later, that this was actually the end of a life cycle of a star, that this is the end of that particular star. Because all its energy was used up, all its fusion of elements into new elements stopped, and the radiation decreased, the whole system collapsed. Now, you're wondering what's going on after that explosion. We have two components, essentially. One component is the central component right here that is a leftover from this explosion. Depending on the mass of this leftover, we get three different possibilities it will develop in. If the star has a mass less than about one or two solar masses, then it will turn into a wide 12th. So in other words, because our sun has one solar mass, our sun will turn into a wide 12th at the end of its lifetime in about nine billion years. The stars that have slightly larger central components about the order of three solar masses, they will turn into neutron stars. And if you are even bigger as a star, you can then turn into a black hole. So it all depends, essentially, on how much is left in the central part after the explosion. Then there is this other component, the gas component. All a large fraction of the mass of the star is actually ejected into the interstellar medium. And we see then this as a gas cloud sitting around the central component. And that has a very important consequence for us. In fact, it's the reason why we are here today. The good news is all these chemical elements that were synthesized for billions of years in that star are actually expelled from this dying star and will form new generations of stars and planets. And that is why we are really here on Earth, because the elements that were cooked in a star are also the elements humans are made out of. 99% of the human body is made up of only six elements, oxygen, carbon, hydrogen, nitrogen, calcium, and phosphorus. So thanks to the fact that all these elements were cooked once in a star and were expelled into interstellar space and were reused later on to form a planet, thanks to this fact we are here today. So that concludes the first part of my talk. And I will continue later on talking about galaxies and star matter.