 Greetings and welcome to the Introduction to Astronomy. In this lecture, we will talk about astronomy of the last hundred years. What has happened and what have we learned over the last hundred years? Note that I will have some lectures like this that are considered enrichment lectures, meaning that they do not tie directly into the class itself or to the textbook. I often use these in discussions or for other parts of the class or for just for students who want to learn a little bit more about certain topics. So let's go ahead and get started and we will start just talking a little bit about that astronomy has changed and we have learned so much more about stars and galaxies and planets over the past hundred years. So many things that we know today that we had no idea about just a hundred years ago. General relativity is an example, something we won't talk about here, but it's only a little over a hundred years old when general relativity was first published and that is our current understanding of gravity. So we are going to look over the coming slides a little bit more detail about what we have learned over the last hundred years. So let's start off in 1923 which as this is recorded is about a hundred years ago and that's when Edwin Hubble made observations of the Andromeda galaxy pictured here and found variable stars in it, Cepheid variables that he could use to determine the distance and that allowed him to determine that it is a galaxy like our own Milky Way. Now before that there was a great debate between astronomers as to whether these spiral nebulae were part of our own galaxy or galaxies of their own and here we find out for the for sure for the first time that these are indeed galaxies just like ours. A couple of years later Cecilia Payne-Gaposhkin pictured here did some calculations to determine that hydrogen is the most common element in stars and therefore in the universe. Before this we figured that the stars would be made up of the same things we have here on earth and we find that no that is not true that her calculation showed us that no hydrogen is actually the most common element. And then in 1929 Edwin Hubble gave us the idea that the universe was expanding. He made measurements to show that the universe the galaxies are expanding and all of the galaxies the most furthest ones are receding faster. So we had the idea previously that the universe was static now we had that the universe was actually changing and expanding over time. As we move into the 1930s we see Clyde Tombaugh here the discovery of Pluto now one of the five dwarf planets known in the solar system. So that was the last time at this point at that point it was the last time a planet had been discovered and of course now that is no longer classified as a planet. Now a few years later Carl Jansky built the first radio telescope detecting radio waves from space and opening up the field of radio astronomy. This is important because it's a new view on the universe a new way to see the universe through a different type of electromagnetic radiation. Similar to this everything had been simply visible light. In 1933 we had the idea that a neutron star that would form in a supernova collapse and at the center of something like the Crab Nebula here a neutron star could form where all of the material in an atom is pushed into the nucleus and therefore crushed together under enormous pressures. Now while this was the theory of it the actual detection of it will not come for another few decades. And Hans Bethe gave us the method that describes how stars are powered through hydrogen fusion into helium atoms and that was how the stars were getting their energy. It was 1938 that we learned how the stars got their energy and were powered. Before that there were various methods that were considered but this was the one that we have that finally has stood the test and now we understand that this is how stars like the sun produce their energy. Now as we move forward a little bit more let's look at the 1940s after World War II now the completion of the Palomar 200 inch telescope which was the largest telescope in the world for over three decades and of course now we have many larger telescopes than this but this was still a tremendous accomplishment and the very largest telescope for 30 years. Jumping ahead almost another decade we start to head into the space age and Sputnik 1 is was launched launching the first satellite into space and that followed closely on just a couple of years later Luna 2 and Luna 3 explored the moon one crashing crashing into the surface a Luna 2 and the other imaging the far side of the moon as seen here for the first time in human history it was the first time we had ever seen the distant side of our nearest neighbor in space because the moon always keeps one side locked toward earth. In 1961 we had the first humans to orbit the earth here is the memorial for that and we're beginning in again the details of the space age and detailed exploration of planets from beyond just earth. So in 1962 we had the first craft to visit another planet think about that just a few years after the first satellite was put into orbit we already sent the first craft to another planet when Mariner 2 flew by Venus. Then in 1962 Martin Schmidt discovers quasars that are actually active galaxies now quasars were known but they were thought they could be stars they were star like objects and now that we knew that they were actually distant active galaxies we know that they are the most distant objects known in the universe. In 1965 panzias and Wilson discovered the cosmic microwave background radiation using the telescope shown here to find the remnant of the big bang that created the universe. In 1966 we find the Luna 9 spacecraft gave us the first soft landing on the moon so the first time a soft landing occurred on the moon and other times we crashed into the surface this was the first time we landed softly preparing the way for manned missions coming up in just a couple of years. By 1967 we see Jocelyn Bell pictured here discovering the first pulsar which was that neutron star we discussed a little while ago rotating very rapidly at the center of the crab nebula. The first manned flight to the moon 1968 giving us this image looking out back from around the moon not on the surface yet but around the moon looking back toward earth then in fact seeing earth as in as going through phases just as the moon does as seen from earth. A year later we had the first manned landing on the moon Apollo 11 landing on the moon here showing the lunar lander the American flag up there in the distance and some of the equipment being set up here. Now coming into the 1970s we had the Uhuru satellite the first chance to look at X-rays from space so we had visible light for a long time then we added in the ability to look in the radio waves and now getting up above the atmosphere we can see X-rays and also in the 1970s starting the satellites so this is the salute 1 the first space station that was launched into that was launched to study the universe from space. Now later on into the 1970s we had the identification of Cygnus X-1 a well known binary star system consisting of a massive star and a dark unseen object and it was identified and confirmed as a black hole in 1972. Now in 1975 we had the first image of the surface of Venus seen from the Venera 9 spacecraft which landed on the surface and you can see a portion of that surface in our image here. Also landing on an object 1976 you can see looking somewhat similar to Venus but definitely some significant differences as well and that is the Viking lander on the surface of Mars looking for the possibility of some kind of life there. The following year Voyager 1 and Voyager 2 were launched to explore the outer solar system so we've seen some studies of our moon Venus and Mars here now heading out to look at the outer solar system but before they got there actually we discovered that Uranus had rings that same year and they would be studied in more detail by the Voyager 2 spacecraft when it reached the planet Uranus. In the late 1970s we had the discovery of dark matter or at least the confirmation of dark matter that we had learned that some material was missing from galaxies that there was more mass there than could be accounted for by the light and other energy being admitted and emitted everything that we could see. Now we also again expanding in our studies we have studied the IRAS satellite to study the universe in the infrared so studying out there looking again at another part of the electromagnetic spectrum. Over the next couple of years in the later 1980s we visited Uranus and Neptune exploring two more planets in the outer portion of the solar system and as we'd seen an image of Venus from the surface previously but Venus cannot be mapped from outside so at least not invisible light but map of Venus by the Magellan spacecraft being fully mapped by radar in 1990. Now continuing on into the 1990s we see the launch of Hubble Space Telescope to explore the universe in visible light from up above the atmosphere and getting above the blurring effects of our atmosphere. Also another satellite in 1992, Kobe the cosmic background explorer detecting ripples in the background radiation of the universe telling us something about the earliest structures beginning to form after the Big Bang. That same year we had the first confirmed detection of an exoplanet meaning a planet outside of our own solar system. Up until this time we only knew of the planets within our solar system and while we suspected others might exist this was the first confirmation of one of these. In 1998 we had the construction beginning on the International Space Station shown here with its solar panel arrays for energy and different modules set up within the International Space Station in a low earth orbit to conduct scientific experiments from space. That same year we discovered dark energy. Dark energy was something that was found to accelerate the expansion of the universe so we expected that the universe would start off with a Big Bang and then slowly slow down as gravity pulled on objects. But what we find is that things are actually accelerating and things are moving faster and faster and that that acceleration will continue and the universe will continue to accelerate its expansion. Now moving on into the 2000s we discovered Eris. Eris was discovered in the outer solar system so we see that here pictured in its moon not easy to see from earth. In 2006 we came up with the classification of a dwarf planet, a formal definition of a planet which is where Pluto's classification got changed and we now have several of these that are actually classified as dwarf planets Pluto, Eris, Makemake and Homea and others which may be classified as dwarf planets as well. There are currently five dwarf planets known. Now black holes, we had detections and determinations that black holes existed. We had one of the first confirmations, one of the first visual evidence of a black hole seen in this case a flare around a black hole. So we're getting more and more detailed understanding of how black holes have occurred and more understanding of those. And we're going to see in 2013 an extrasolar asteroid, meaning that it is an asteroid not part of our solar system but from another solar system that traveled in to our system. So it was ejected out of its system as much material is ejected out of our own solar system when it formed and another traveled in to just happened to travel in to our solar system. Moving on we had the exploration of Pluto by the New Horizons spacecraft giving us great detailed images that are still being studied of the distant dwarf planet. So in 2015 we had the very first detection of gravitational waves from two coalescing black holes and the gravitational waves occur when objects are moving, when any object with mass is moving. But the gravitational waves are strongest when that object moves fastest. So we need very high mass objects to be able to detect these very weak gravitational waves and the first confirmed detection of them was in 2015, nearly 100 years after they were predicted by Einstein in his General Theory of Relativity. Again in 2015 the first confirmed Earth-like planet found to exist in the habitable zone of a star. So finding more planets that may be habitable. Existing in a habitable zone doesn't mean it is habitable, simply that it's going to be at the right distance for liquid water to be able to be present on the surface. In 2017 another source of gravitational waves from a neutron star collision was detected first of all in gravitational waves but was able to be observed invisible and other wavelengths as well. So continuing the new field of gravitational wave astronomy. Now as we come into the current, more current things, we have 2019 the event horizon telescope gave us this image of the black hole at the center of a galaxy known as M87. And we see the shadow of the event horizon of the black hole there along with material around that black hole. In 2020 Osiris Rec seen here collecting a sample of the asteroid Bennu comes down, grabs that material, sprays that material up which is then captured and then is going to return that to Earth and that is scheduled for the later part of 2023. In 2021 we also had the Ingenuity Helicopter flying on Mars that came with the Perseverance rover and that was our first time trying to fly through the atmosphere of another object. So not just going through to land but actually traveling through to look, take off, take images and be able to study. Now of course getting up above the ground makes things travel a lot easier than it is with the rovers that have to worry about obstacles. So a chance to have a different way to be able to explore objects. And then in 2022 we had the Dart mission and that was an impact on an asteroid or actually the satellite of an asteroid to try to change its path and it was considered a planetary defense mission that could we actually change this and it was found that we did change the orbit by about half an hour by the impact of a spacecraft on a much larger asteroid. So perhaps in the future we would be able to redirect an asteroid that was coming toward Earth. So that gets us up almost up to date and what we'll see summarize here. We talk about things like less than a hundred years ago. We didn't really understand galaxies or what they were or how stars worked. Those are things that we talked about in this lesson. The space age gave us a revolution in discoveries in astronomy and who knows what is coming next and what will be that next big discovery. So that concludes this lecture on a century of astronomy. We'll be back again next time for another topic in astronomy. So until then have a great day everyone and I will see you in class.