 Greetings and welcome to the Introduction to Astronomy. In this video we are going to talk about the last hundred years, the last century's worth of astronomy, and hopefully give you an idea of how things have changed over that time. So let's go ahead and get started here. And what we see is, you know, what do we know about astronomy over this, but there has been great progress in astronomy over the past hundred years. If we think about it, general relativity, our current understanding of gravity, is only a little over a hundred years old. So if we think what we think about is that this discussion will give us an understanding of what we have learned about since general relativity and over the last hundred years or so. So this will not be complete, obviously I can't go through everything that's been discovered over the last hundred years, but I try to hit on some of the very important topics that have been covered. So let's go ahead and get started here with these and we'll go back to the 1920s. So what was discovered in the 1920s, well one of the things that was discovered in 1923 is that Edwin Hubble determined that the Andromeda nebula at the time is actually a galaxy like our own Milky Way. What he saw were variable stars in images that he took of the Andromeda galaxy and because he was able to determine that they were Cepheid variables like those in our own galaxy, he was able to use them to determine distances. So prior to 1923 we did not know for sure that galaxies like the Andromeda or what were called spiral nebulae were actually galaxies like our own. In 1925 we saw Cecilia Payne Gaposhkin gave us the idea and showed us that the hydrogen is the most common element in the universe. I'll tell you many times that hydrogen makes up 90% of the atoms in the universe, but this was not determined until analysis of spectral lines by Cecilia Payne Gaposhkin working on her thesis that showed that the abundances of hydrogen were tremendous and it was something that was very difficult to accept at the time and she had to even put a disclaimer that said that this could not possibly be correct, but it turns out that it was and in 1925 we did learn that hydrogen was the most common element in the universe. Also in the 1920s we learned that from Edwin Hubble, coming back to Hubble, that he determined that the universe is expanding and that distant galaxies are receding even faster. So prior to this in the before the 1920s we did not realize that there were other galaxies that hydrogen was the most common element in the universe or even that the universe was expanding. Now as we move on to the 1930s and see what we learned there, first thing to be discovered in 1930 itself was Clyde Tombaugh shown here discovered Pluto and Pluto at that point was considered the ninth planet and was actually detected by searching a very careful search looking for an object out beyond Neptune. A couple of years later in 1932 Carl Jansky was able to bring us the beginnings of radio astronomy and we see his initial radio telescope here and he detected radio waves from the center of our galaxy and that opened up a whole new field of radio astronomy before 1932. The only astronomy that was done was through visible light. Now that has expanded and now we can look at radio waves from space as well. A year later in 1933 we saw that neutron stars were discovered or were at least theorized that they could exist and Walter Bada and Fritz Zwicky described the neutron star that would form in a supernova collapse and that is now known to exist at the center of things like the Crab Nebula here and a few years later towards the end of the 1930s we found that we learned what stars were, how stars produced their energy and that was something important, Hans Bethe gave us the method of nuclear fusion that we use today where essentially four hydrogen atoms go through a process and become a helium atom and that is the nuclear fusion that powers the stars but prior to 1938 we still were working on trying to understand how the stars could be powered. Now as we move a little further we'll come into the 1940s and early 50s and let's take a look at some of those. In 1948 we had the Palomar telescope seen here and that was the largest telescope in the world for three decades. Later into the 1950s a decade later we find that Sputnik 1 was launched and we can see that here. So Sputnik 1 being launched and that was the first satellite so here is an image of a simulation of Sputnik so we can see a picture of that here and that was the start of the space age and we're going to see a lot of what comes next, we'll be based on that. A little while later we actually just two years later in 1959 Luna 2 and Luna 3 discovered the moon crashing into the surface and imaging the far side so Luna 2 crashed into the lunar surface the first time we put something on another planet. Luna 3 actually gave us an image of the far side of the moon for the first time so before that we had not known what this had looked like, what the far side of the moon had looked like and while this is not a great image it still was very important for our understanding of the universe what were things what were things like on the other side of the moon until 1959 we did not know what the far side of our nearest neighbor in space looked like and then in 1961 just four years after the first artificial satellite was launched we had the first humans to orbit the earth and we show here in a memorial to those but that was the first humans to earth and only less than a decade later we would actually put men on the moon. Now as we look through the 60s we're going to see things start to break down a little bit more here just because so much was going on and in the 1960s in 1962 just a year after we put a first human in space we also saw that Mariner 2 shown here became the first craft to visit another planet and it went to Venus and flew by Venus. In 1966 also in 1962 Martin Schmidt was able to discover that quasars are actually active galaxies and therefore the most distant objects quasars are quasi stellar radio sources meaning they looked like stars but were eventually found to be supermassive black holes receiving a lot of material and giving off tremendous amounts of energy these became the most distant objects known in the universe tracing out to 10 billion light years or more away. A few years later in 1965 Pensaias and Wilson shown here were actually discovered the cosmic microwave background. This was a prediction of the Big Bang so the Big Bang predicts that this should be here and we found this remnant in 1965 that they found when studying the sky with their telescope not looking for it but actually looking to minimize the amount of noise and they found this background noise that was coming from everywhere in space and that was the discovery of the background radiation which was a big piece of evidence towards the Big Bang as the model for the origin of the universe. In 1966 we had the first soft landing on the moon. I mentioned a landing on the moon the first one was a crash into the moon but this was Luna 9 actually gave us the first soft landing on the moon. And as we move onward then we see into the next region we'll look at the late 1960s to the early 70s and a lot went on there as well as we see. First of all Jocelyn Bell discovered the first pulsar. We looked at the idea of neutron stars but the first pulsar was actually discovered in 1967 looking at radio emissions. In 1968 and just remember we're only 7 years from the first man in orbit and now we have the first manned flight to the moon. So we actually traveled to the moon this time and that was the Apollo 8 mission that traveled and went around the moon and came back. So they didn't actually land on the moon but again were the first people to see the earth from the distance of the moon and to see even this case just a partial phase of the moon. Now just a year or so later we did have the first manned landing on the moon shown here this would be Apollo 11 landing and that was the first manned landing on the moon in 1969 again just 8 years after the first person was in space. Now not everything had to do with the moon as our last couple did but there were also a lot of other things going on. In fact the Uhuru satellite was launched in 1970 and this again like radio astronomy by Carl Jansky opened up another window on the universe. This was the first time we could actually study x-rays from space so we were able to look at what x-rays were doing and that's important because they are unable to penetrate the earth's atmosphere to be seen from the ground. And also in the early 70s we had the Salyut 1 the first space station was launched so our first space station and a precursor to the international space station today. Now throughout the rest of the 70s we had of course more things going on. First of all in 1972 Charles Thomas Bolton actually identified Cygnus X1 as being a great black hole candidate so we could see the black hole with the disk of material spiraling around it here in this artist's conception but the first measurements based on the orbit of the mass showed us that the mass of the object there at the center of that red disk had to be too massive to be anything but a black hole. A little bit in a couple years later in the mid 70s we got our first images of the landing on Mars, sorry the landing on Venus and that was images of Venera 9 sending back images of the surface of Venus. So that was a chance to really see the surface of Venus for the very first time because it is constantly shrouded in clouds. And the following year 1976 we had the Viking landers on Mars which were landers were able to explore Mars in detail and begin to look for signs of life and their initial searches for life were unsuccessful but we still look for that today. The following year in 1977 Voyager 1 and 2 were launched to explore the outer part of the solar system. Voyager 1 would visit Jupiter and Saturn and Voyager 2 would go on the grand tour not only visiting Jupiter and Saturn but also Uranus and Neptune visiting four planets and giving us our only knowledge to date of the two outermost planets in the solar system. In 1977 we discovered the rings of Uranus and those were discovered when Uranus passed in front of a star and the star dipped in brightness as it came close to Uranus so as the planet passed here it would get dips in brightness as it passed each of these rings before it actually dipped out completely as it passed in front of as past behind the planet as the planet passed in front of the star. So that was something important because Voyager 2 was launched about that time and Voyager 2 would get a chance to actually study the rings of Uranus and now we knew in advance that they were actually there. In the later later 70s and through the 80s we were continuing to make again great strides and what we find in first of all is the confirmation of dark matter by Vera Rubin in 1978 and we found that dark matter was a very important part of the universe and makes up a lot of the matter the vast majority of the matter in the universe is some kind of mysterious dark matter that is quite different than the ordinary matter that we're used to. In 1983 we launched a satellite to study the sky in the infrared and that was the IRAS satellite and we were able to do that that was able to then study the sky in the infrared for the first time. Now we could do a little bit of infrared astronomy from the surface of the earth and from balloons and high-flying aircraft that this was the first satellite permanently in orbit that was able to study the study the sky in the infrared part of the spectrum. In 1986 we visited Uranus for the first and only time so we were able to see Uranus for the first time and study its rings. A couple of years later Voyager 2 made its way to Neptune and was able to study Neptune for the first to first and again the only time we have actually looked at Neptune up close and we cannot see it with near this kind of detail from the earth and then finally in this section we saw Venus for the first time in great detail. We'd already seen a few images of parts of the surface of Venus but we'd never been able to map the surface and in 1990 the Magellan spacecraft mapped the surface of Venus not with visible light because we can't see visible light through the clouds but with radar and able then to understand the surface of what the surface of Venus was like. Now as we continue on getting into the 90s here and what we see is one of the very early things in the 1990s was of course the launch of the Hubble Space Telescope so that was a very important thing at Hubble still going as we speak right now and that has really opened up over nearly 30 years worth of studying of the sky. In a couple of years later in 1992 Koby the cosmic background explorer was launched and that detected ripples in the radiation from the very background radiation of the universe. These ripples were actually then tell us something about how the very earliest structure in the universe formed. The same year we actually had the first confirmed discovery of an exoplanet so think about that prior to 1992 we only knew of the planets in the solar system and that was it. This was the first discovery of a planet first confirmation of a planet outside of our solar system. In 1998 we began construction of the International Space Station. So International Space Station seen here in a more complete sense was actually started in the late 1990s and also in 1998 we made the discovery of dark energy. Dark energy has been found to cause the universe which we knew was expanding but caused the expansion to accelerate meaning that the expansion is increasing at an increasing rate so the velocities were slower in the past and are getting faster and faster as we head into the future and this gave us that discovery that dark energy along with dark matter make up about 96% of the mass and energy in the universe. Well let's move into the new the new millennium here into the 2000s and what we find some of our discoveries first of all in 2005 a we found the heiress was discovered and heiress was another object in the Kuiper belt much like Pluto and part of that led to in 2006 that the International Astronomical Union formally defined what a planet and a dwarf planet were so that made that there were eight planets and we now have at this recording five dwarf planets that are known the eight planets being the standard planets that we know Mercury Venus Earth Mars in the inner solar system Jupiter Saturn Uranus and Neptune in the outer solar system and the five dwarf planets including Pluto so we had actually never defined previous to that we had never defined what a planet was and now we have found far more so there are other dwarf planets such as heiress which was discovered in 2005 but also Macha Macha and Hamea were discovered and Ceres was considered and moved into the class of a dwarf planet as well in 2012 we got the first confirmation of black holes so first visual confirmation of black holes by Suvi Ghizari and that gave us visual proof of the existence of black holes for the very first time and in 2013 we actually discovered an extra solar asteroid meaning that this is not an asteroid that was part of our solar system but something that came from another solar system and traveled through interstellar space and came close to our solar system to be able to be studied so it was the first time we had seen an interstellar asteroid and then as we continue and look at the more recent discoveries 2015 through 2017 and what we see is that first of all in 2015 new horizons explored Pluto and gave us our first images of that dwarf planet from earth we could only see a very small amount of light and dark detail but could see no deep no great detail of it and that continued on new horizons continued on and in 2019 actually explored Ultima Thule and continued its mission and was able to look at another much smaller object out there in the Kuiper belt now what else we saw we did get in 2015 also was the first detection of gravitational waves now this was a prediction of Einstein's relativity his general relativity from about a hundred years before however they were too faint to be able to be detected and it wasn't until 2015 that we had sensitive enough instruments that we could detect the gravitational waves from two colliding and merging black holes and in 2017 we actually were identified we're able to identify the source of gravitational waves from colliding neutron stars so if we see an artist's conception here to neutron stars colliding together to form a black hole and we could see that not only in gravitational waves but now we were able to identify it in optical and in other wavelengths so the progress in astronomy will continue these are just some of the things that we have done over the last hundred years in astronomy and as you go through an astronomy course you have to think about all the things that you learn and how little of that was actually known even a hundred years ago so let's finish up here with our summary again just to kind of summarize what we looked at just a hundred years ago we did not understand galaxies or what they were or how the stars worked those are things that we have only led learned about recently the space age gave us a revolution in astronomical discoveries able to observe at other wavelengths so we could observe x-rays at infrared and other wavelengths that we could not observe a hundred years ago and able to directly explore the planets not just through telescopes here on earth but by directly going there and of course new discoveries are coming and who knows what the next big discovery will be 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