Transcript: The Future of Astronomy

Download the transcript

Fraser: Astronomy Cast Episode 188 for Monday May 3, 2010, The Future of Astronomy. Welcome to Astronomy Cast, our weekly facts-based journey through the cosmos, where we help you understand not only what we know, but how we know what we know. My name is Fraser Cain, I'm the publisher of Universe Today, and with me is Dr. Pamela Gay, a professor at Southern Illinois University Edwardsville. Hi Pamela, how're you doing?

Pamela: I'm doing well. How are you doing, Fraser?

Fraser: Good, but summer doesn't seem to have arrived yet here on the west coast… it's just been cold and wet and rainy, and we're in June…

Pamela: Oh, I'll trade! We're hot and muggy, without air conditioning, and daily thunderstorms…

Fraser: Well, I was wondering if somehow the volcano would… the European volcano might have had some impact by darkening the skies and causing the summer… the year without a summer…

Pamela: No… they're saying that it was the wrong part of the atmosphere for it to have an effect… it wasn't Krakatoa or Pinatubo… I think was how you pronounce it… No, Katla… no not Katla… we're waiting for Katla… the E–unpronounceable Icelandic volcano… no it just spit on the air industry, not on the air conditioning industry.

Fraser: Right. Oh well, I guess I can't blame it on volcanism.

Pamela: Well, if Katla goes, you can blame Katla.

Fraser: Ok. Alright, well, we spent 5 episodes telling the story of astronomy so far… how we got from the work of the Babylonians to the modern discoveries made in just the last decade. But now we want to look forward… setting the current science missions and experiments to uncover the mysteries that astronomers are hoping to solve. So, with this episode, it's going to be another one of those jumping all over the place episodes and obviously there is no way that we can accurately predict what discoveries are going to be made in astronomy to any great extent. No one could have predicted dark energy. Those happy, random… oh, that's interesting… discoveries that astronomers make. But at the same time, there are broad themes, there are missions going up, there are mysteries, there are better experiments being developed which should then turn around and give better results, and maybe solve some of the open problems. And so… we've kind of broadly classified this… so let's start by staying close to home… and talk about some of the stuff that's going to be happening in the solar system and use that as a way to know what we're looking for.

Pamela: Well, I think closest to home are the series of missions that are going to be looking at Mars and the moon and trying to figure out where should we go next… what should we build next… what should we do next… so we have GRAIL and LATTES getting ready to go that are going to work to better understand the moon, to better understand its composition, its atmosphere, we're going to be looking at Venus and its chemistry and dynamics. We're going to be hopefully going and landing a laboratory on the surface of Mars and having it be a laboratory that can move itself around a bit. The Viking missions were awesome because they sat there on Mars' surface, scooped up what was in reach, and very carefully looked for signs of life, signs of chemistry, and actually got inconclusive results because we realized that there were things that we forgot to take into consideration about the Martian climate.

Fraser: Well, I mean up until now, NASA's take on Mars has been very conservative. Was there evidence of past water on Mars? Yes. Is there currently water on Mars? Yes… frozen. Is there ice water underneath the polar ice caps of Mars near the surface? Yes. But come on… let's get to the question… is there life on Mars? That's the question, and that's the one that they need to solve.

Pamela: And this gets to… the problem of getting Congress to sign off on things of… hi, we're going to look for little green microbes… not little green men, just little green microbes… and that's a complicated task. But if all you're doing is looking for water, looking for things that human beings would need if we went and took over Mars, that's easier to sell. It's also very controversial… how do you say if there's life or not? We had the funding with the early landers… we had the question, is there life? We had the experiment, and the experiment was inconclusive… that's a failure to many people. It's not in science. Inconclusive means you have new questions, new things you need to answer. Inconclusive is awesome and cool and leads you to new directions of discovery. But it's hard to explain that.

Fraser: So, there are plans in the works to develop a mission just to analyze the methane in the atmosphere of Mars. And as you said, there's the Curiosity rover that's going to be down over the surface of Mars. It's a nuclear powered, SUV-sized, rover with arms and laboratories inside it, and it is going to be looking for life. It's going to be looking for the chemistry of life on the surface of Mars. Maybe within the decade we should be able to come up with a pretty good answer…

Pamela: That's what we're hoping. We're hoping that the next big launch window, it will be what goes up. And then beyond that, we're also looking at the Mars sample return mission because by sending a lab to Mars, we're limited in what we can do. If any of you have ever worked in a lab, you know there's always the day where you go… dang it, I need… and you go borrow something from a friend… you go grab a tool, you order something online, you get a new reagent. If you're on Mars, you can't do that. But, if instead we go out and we grab a bunch of rocks like we did with the moon… with the Apollo missions and the lunar sample return missions… if we go to Mars, grab a bunch of rocks, bring them back to Earth, then you have that ability to run unimagined experiments. Now there isn't a secure timeline on the Mars sample return mission. We're hoping sometime end of this decade… beginning of the next decade… somewhere in the 20 year plus or minus… that maybe we'll be able to get our rocks.

Fraser: So, when we're making our big list of mysteries we were talking about that… is there life on Mars… we will either find results inconclusive–which means that if there is life on Mars, there isn't much. It's pretty well hidden, and isn't pooping and isn't breathing. And if there is life on Mars, the more interesting question is going to be is it related to us… and how? Are our two planets connected? And when?

Pamela: Panspermia…

Fraser: Yeah, so even if we do find life on Mars, once again, if the planets are connected then it means that life moves from planet to planet… maybe from solar system to solar system around the whole Milky Way. If we find life on another planet or orbiting on another star, maybe we're related to that life as well. So Mars is just one place… we're going to look at other places in the solar system, as well. Although there's less definitive plans for that.

Pamela: Right. Juno is one of the next big missions we're looking at… to go and explore the Jupiter system. I say Jupiter system because even though Jupiter's not a star, it is in many ways a model of a solar system. You have this almost-star orbited by moons that it is able to keep warm, it's just not warming them radiatively like the way our sun warms the earth… instead warming them gravitationally by squishing them like little squishy balls until they heat up.

Fraser: Exactly… grab a squishy ball or grab some Silly Putty and just smoosh it back and forth and you'll be warming it up in the same way.

Pamela: And so here we have this system with… well, I think that Europa is perhaps one of the greatest mysteries in our solar system. Clarke, in his 2010 Space Odyssey books… that was the moon that the aliens were from, or at least the big black monoliths… and you're supposed to leave it alone. Well, we're not going to leave it alone. We're not only not going to leave it alone, but we're going to burrow through the ice and again, look for life. That's one of the amazing things… we are now entering the period in our space explorations where looking for life is one of the everyday questions. We're going to go to Mars–we're going to look for microbes. We're going to go to Europa–we're going to dig through the ice and see… is there life in the liquid ice beneath the surface.

Fraser: And we're not going to stop in looking at the planets here in our solar system. I mean, now we're at the point where every month, every week, the total number of planets that have been discovered is in the 100s, but the final goals haven't been reached yet. All we've been discovering so far are hot Jupiters and mega-Neptunes, and super-Earths. But the goal, of course, is Earth-sized worlds with life, orbiting other stars.

Pamela: Right. And with the Corot mission… the European Space Agency mission to basically look for things that pass in front of the stars that they're orbiting.

Fraser: You said that very quickly… Corot… C-O-R-O-T…

Pamela: Yes, it's French… which is not one of my best languages to pronounce. This is a mission that is starting to turn up things that are fractions of Jupiter's mass. It actually has found one object that is 0.015 times the mass of Jupiter. It's about a tenth of the radius, so it's still not an Earth-sized body, but we're getting smaller. And it's again very close in to its star… pretty much on top of its star… its semi-major axis in astronomical units is 0.02, so it's on top of its sun. But it's still tiny. So we are finally finding tiny things. We also have the Kepler mission up, and between Corot and Kepler the rocky worlds are going to be found. That will hopefully allow us to once and for all have an understanding of the diversity of what solar systems look like. When you and I were kids, what was the solar system model that we both learned? It was rocky worlds next to the star, gas giants out at the edge. We now know that it's wrong. But, what else is there?

Fraser: Right. And so with Kepler and Corot, we're not going to get much more than rocky worlds orbiting other stars. It's going to be a whole other generation of telescopes that need to show up to take things to the next level.

Pamela: And this is where we start getting into the weird stuff, with missions like James Webb, you have the ability to start studying planetary atmospheres if only you don't have to get blinded by that silly star that planets are orbiting. And so we're looking at how do we build giant orbiting shields that can move into a position such that they block out the light of that offending star allowing you to resolve the planet nicely. So we're starting to try to figure out what are the ways that we can start imaging planets, start looking at atmospheres, start… well, maybe finding life by the signature it leaves in planetary atmospheres as observed with our next generation of space telescopes.

Fraser: So, when do you think that will be done… if you were just to guess, would you say… Kepler and Corot won't be able to do it… James Webb might be able to hint at it… but we're looking at something after James Webb… so we're looking at an as of yet unnamed oh, terrestrial planet finding mission, for example.

Pamela: Right, right. This is where we start getting into the… we know how to solve this problem if only NASA or ESA or JAXA or one of the other space agencies just had enough money to build all the cool science toys we need. This starts to become a question of economics more than of technology. If we can get a good solid global economic recovery, within the next ten years. But I think unfortunately a lot of money is going into solving problems other than what is the atmosphere of alien worlds. I want to know what the atmosphere is of alien worlds!

Fraser: So we'll probably get an answer for the solar system within about ten years… and maybe other worlds within 20. Ok, so that's life… very important…

Pamela: Very cool…

Fraser: But there are more concepts in astronomy which we're going to want to get some answers to… there's two big ones, of course. We've talked about dark matter and dark energy. Dark matter…. we're starting to really narrow in on that one right now. Some big discoveries happened in the last couple of months. I think we're actually thinking of doing another episode on dark matter at some point to finally update a concept that we presented back at the beginning of the show, which now there's enough news now that we can take another spin at it.

Pamela: Right.

Fraser: But, there's some wonderful tools that are going to help us figure out what dark matter is.

Pamela: And what's really interesting is that this isn't a matter of strictly looking up anymore… now we're also digging into the ground, and just as we used giant tanks of fluid to detect neutrinos, it looks like very similar technologies are going to be used to detect dark matter particles as they go through the earth system. It also looks like with the Large Hadron Collider, just as we're hopefully creating Higgs… Higgs bosons, which we also did a show on…. maybe, just maybe if we're lucky, the lightest weight of the super-symmetric particles, if that theory is correct, will also be detected and those would also be another form of dark matter. So we're getting to the point where through ground-based experiments with the Large Hadron Collider and ground-based detectors with these giant underground tanks that they have in Japan and the States and Canada… usually in coal mines or other mines, we're going to start directly detecting particles… particles of dark matter one by one.

Fraser: Particles… perfect. And then and you can see how we've traced that lineage. We've gone from maybe we don't understand gravity, or maybe there's a bunch of particles that we can't see that are the majority of the matter in the universe to… it's pretty clear that it's the particles, and now we just aren't really sure what those particles are and where they came from and why they're there and what their characteristics are and how they interact with other things or don't and so that's what the work of the astronomers are going to be. I wonder if they're ever going to come up with a new name and then so we can stop calling dark matter, which bugs everybody, and just give it the new name… I don't know…

Pamela: We kept big bang, and it was meant as an insult…

Fraser: Black holes…

Pamela: Yeah… so we keep keeping these insults and clinging on to them.

Fraser: So the more mysterious one is dark energy, which is… not really connected to dark matter at all.

Pamela: No… utterly unrelated.

Fraser: But still in people's minds because of the "dark" and the "dark" it's connected, but… yeah it's a whole separate thing. It's this mysterious force accelerating the expansion of the universe, discovered in 1998, and astronomers still have no idea what we're looking at…

Pamela: Right. And just trying to figure out… well, how do we best figure out what it is. That itself is even in debate. This is one of those great cases of watching science try and figure out a mystery in the public realm. There was a committee convened to try to figure out how do we figure out dark energy… and one of the debates that came out of it… and this is Rocky Kolb and Simon White… was do we do like we did with the cosmic microwave background and start building very specialized, very dedicated instruments like we did with the Wilkinson Microwave Anisotropy Probe – WMAP- the really great satellite that got us a final definition of the universe is 13.7 plus or minus 0.2 billion years old and nailed the expansion rates… and just so much really great science has come out of this mission, and now we have Planck, another narrowly-focused mission working to study the cosmic microwave background in even greater detail, do we take that approach?

Fraser: And just really narrow down and confine dark energy… at this age of the universe this is how fast it was pushing, and now… to the left and to the right… and to really understand its characteristics?

Pamela: Not quite. No, it's more do we build missions like that… because the other alternative is… well the Hubble Space Telescope was built to figure out what is the expansion rate of the universe. But that's not the only thing that Hubble does. WMAP was built to study the cosmic microwave background, and yes… some ancillary science has come out, too, but it studies the cosmic microwave background. Hubble… heck we're using it to study light echoes from quasars, we're using it to study planets, we're using it to…

Fraser: …discover rings around Neptune…

Pamela: Right. So it's focus is not just one thing. It's a mission that was built that individual scientists can put in for time to do individual research questions. And it's an observing tool. It isn't a one-use experiment. And so this is the debate… in trying to solve dark energy, do we focus our dollars on building one-trick ponies… instruments that can only be used to study dark energy. Or, do we take the Hubble Space Telescope approach and so we're right now so far away from an answer that we're not even sure what sort of tools to bring to the question.

Fraser: And so that is what…. it might go down one the way which is very similar to WMAP… there'll be the Dark Energy Explorer and its only job will be to carefully analyze just the supernova in all directions to really calculate the expansion of the universe in the past and now, or a nice big generic tool like Hubble that can… one of the things it can do is analyze supernovae.

Pamela: Yeah. And the thing that comes out of this is this is also a change in how we do astronomy. Because if you look at the author lists of projects of WMAP, like Planck, and even like Kepler in many cases, you have teams of hundreds and sometimes thousands working to solve one question… each person dealing with their one specific part of the data pipeline. But you look at Hubble, and you still have the occasional two author papers, where it's individuals solving the personal question of their lifetime.

Fraser: Yeah, in many ways it's very difficult to really predict what people are going to be… what questions are going to be answered… because as you said, it's not like… think of the Apollo mission, right? What was the goal of the Apollo mission? To land humans on the moon and return them safely to Earth. And you know that the whole mission profile, and all of the people and all of the tools and all of the software is all being developed for that purpose. But in many cases now, it's people who are going to be… I'm going to use this to study pulsars and try to get a better sense of some mystery of pulsars, or I'm going to use it to study gas clouds. But, is the emphasis… I mean there's the large telescopes… the Overwhelmingly Large Telescope and the Very Large Telescope and the various arrays of telescopes and the different… so would you say that the tools are more general tools? Like, let's have some good tools in the radio. Let's have some good tools in the infrared… Or are there some specific-purpose tools being built?

Pamela: I think one of the things that's happening now is a really neat compromise where we see things like the Large Synoptic Survey Telescope that is getting built with the core mission of finding any rock out there capabable of destroying the planet Earth and figuring out its orbit well in advance. That's its core mission. But it's also going to image the part of the sky available to it every three nights, and in the process of doing that it's going to turn up types of variable stars we can't even imagine. It's going to increase the number of novae and supernovae that are getting detected on a regular basis. It's not just going to find the Earth-endangering objects, it's going to find Kuiper Belt objects, it's going to give us a solid and statistically significant understanding of how our sky is changing at the cadence of every three nights of a new picture of what's changed. That is pretty amazing, and there are communities of astronomers trying to sort out what can we do with this wealth of information that's coming our way? So there's one scientific central goal that the telescope has to be able to solve–where are the rocks that are going to destroy the planet Earth? But they're building the system using sets of filters and other characteristics are being done to be sure that other science can be done, as well. I think it's a dual-purpose model that we're going to be seeing in the future.

Fraser: Right, and one mission that should change everything or should push things out to the next level is going to be the James Webb.

Pamela: Right. And this telescope that's going to go out beyond the moon… it's going to hang out in the LaGrange point in the shadow of the moon, observing the infrared sky… and it will allow us with its core mission to see the first galaxies, to see our universe clear itself out as it reionizes. That will tell us exactly how it is that galaxies formed…. top down? bottom up? both? We think we know the answer is both. James Webb will answer that question… it won't be "I think," it will be "I know."

Fraser: Right. And right now we see press releases–most distant galaxy observed… where Hubble has used gravitational lensing to spot some galaxy that's 500 million years after the universe formed, or 700 million years… but with James Webb, we should get right out to the edge, to the wall, to the limit… and that's going to be really neat.

Pamela: And it won't just be the supergiant, weirdo, huge galaxies… it will be a wealth of different galaxies. So we'll be able to see not just how the giants formed, but… we won't see the dwarfs, but we'll see the normal things. We'll see the small smudges coming together. What we know from Hubble, and from other deep ground-based surveys, is the further back you look, the more chaotic galaxies appear. They start to go from nice pretty spirals and boring puffballs to "dead bug" in appearance. Well, it's true..

Fraser: Yeah, no, no… I know…

Pamela: And we're just going to be able to see how is it that galaxies evolve by seeing them piecemeal in all their different sizes across all the different eons of evolution.

Fraser: What about the more exotic stuff, like gravitational waves?

Pamela: So, there's a few missions that just keep falling off the funding list and LISA is one of them, and that's an interferometry mission. A mission with multiple spacecraft that keep each other co-orbiting, but are connected through lasers and as the distance between the individual spacecraft varies, you can pick that up through interference in the laser beams and nominally that would allow you, if you have a really good gravitational model for the planet they're orbiting, to start detecting gravitational waves from supernovae, from merging black holes, from merging neutron stars. There's a whole variety of different events that should cause gravitational waves, and we've seen evidence of gravitational radiation in black hole binary systems and neutron star binary systems, but we haven't seen any of these stupid waves! We can do it in math, but we can't see them! If LISA can just get funded, and we can get all the calibration data we need, maybe we can see them and someone can get a Nobel prize.

Fraser: And then what about some of the really weird stuff, like other dimensions… string theory… worm holes…

Pamela: Yeah, we don't have any…

Fraser: …white holes… oscillating universes… and branes….

Pamela: No, no, no… string theory, we don't have any…

Fraser: Probably not… you can't say no because there's a famous quote, right? When a scientist tells you that something could be possible, then it probably is. And if it's impossible, then they're most certainly wrong…

Pamela: What I was going to say is that with string theory, we just don't have any solid experiments that only say string theory is the possible answer. We have ones that would say "not string theory," but we don't have anything that says "string theory and only string theory." So with that one, the theorists need to catch up more. But with brains and oscillating universes and all those sorts of things, those aren't on anyone's radar right now, so…

Fraser: …no experiments.

Pamela: Not in the near future.

Fraser: But someone could…. once again, you could have some discovery that comes out of nowhere and somebody… some alien shows up and says take a look through my universo-scope…

Pamela: I want my aliens in microbial form, please.

Fraser: Alright, with laser beams…

Pamela: That's like sharks with lasers, except now we have microbes with lasers…

Fraser: Well, let's meet back in 20 years, Pamela, and find out how much of this stuff came true.

Pamela: Sounds like a plan.

Fraser: Alright, we'll talk to you next week.

Pamela: Ok, bye-bye.

Transcript: History of Astronomy, Part 5 – The 20th Century

Download the transcript

Fraser: Astronomy Cast Episode 187 for Monday April 26, 2010, History of Astronomy, Part 5 – The 20th Century. Welcome to Astronomy Cast, our weekly facts-based journey through the cosmos, where we help you understand not only what we know, but how we know what we know. My name is Fraser Cain, I'm the publisher of Universe Today, and with me is Dr. Pamela Gay, a professor at Southern Illinois University Edwardsville. Hi Pamela, how're you doing?

Pamela: I'm doing well. How are you doing?

Fraser: Good. I get uninterrupted Pamela time for like the better part of a month before you're travelling, so we've got a lot of shows that are going to be coming out hopefully very quickly, so I hope this will show our commitment to you, the listener, as you get buried in audio. So, I think this is going to be the last part of the history of astronomy. So, let's go into it. So many of the modern ideas in astronomy happened right in the 20th century… dark matter, the big bang, inflation, quasars, black holes, neutron stars, pulsars, and even dark energy. So, with so many discoveries in one important century, let's get started. Alright, in episode 4 we wrapped up right with Hubble's discovery that those blurry spots that he thought might be nebulae, were actually whole other galaxies… which means that the universe is much bigger and the Milky Way is just another galaxy in a gigantic universe. And you mentioned that you've met astronomers who remember that…

Pamela: Right…

Fraser: Which is quite amazing to think… I mean you look at all the books and you think about all of our modern concepts of astronomy, and the sort of size and scale of the universe, that really plays a big role in that. And yet, all of the stuff just came in the last 70… 80 years. So, let's proceed from Hubble's discovery of our place in the universe and what would you say is the next big discovery that was made?

Pamela: Well, I think it was figuring out our place in our own galaxy in 1927 with Oort. Up until that point, we still didn't know where in the Milky Way we were. There were people who put us in the center, there were people who just didn't know. But the problem is, you look out in the disk and because of dust, because of the density of stars, you can see within the disk the same distance in all directions.

Fraser: Right, I remember that it was Herschel who first took a shot at that, right? Tried to do a… tried to figure out our place and try to map out the size and shape of the Milky Way… but it was hopeless because he didn't realize that the gas and dust would be obscuring our view towards the core of the galaxy, and so he had no idea what the real true shape is.

Pamela: And it's really frustrating because star counts can't get you there, and so we had to come up with something new, and this is where globular clusters come into the picture. They're rich with pulsating variable stars and pulsating stars are distance indicators, so we can tell where they are. And Oort went out and he started measuring the distance to the globular clusters and plotting them out, and figured pretty accurately where we are within the Milky Way… and we're still figuring out "accurate"… but that we're off to the side… and he was able to finally say the center of the Milky Way is in the constellation Sagittarius. We didn't even know that amount of information until 1927.

Fraser: And so it was more of like looking for spots that were missing where there weren't globular clusters and to realize that those were blocked.

Pamela: Well, and not only that, but the thing with globular clusters is they form a sphere… a nice friendly round distribution around the Milky Way galaxy. And so he was able to plot the distances to the ones that we can see. And we can't see the ones that are on either side of the disk… but by plotting out the distances to the ones that he could see, and knowing what parts of the sky were obscured, he was able to say… Ah, this is a sphere! And I see where we are within the sphere, and I can see where the center of the sphere should be… and that's towards Sagittarius.

Fraser: Right, and of course we know the name because the Oort Cloud was named after him.

Pamela: He was the one that… theoretically he didn't have observations… we still haven't observed the Oort Cloud. He was the one who theorized that the Oort Cloud is out there serving, perhaps, as part of the source of comets…. that there should be this spherical distribution of material around our own solar system just like there's this spherical distribution of material around our Milky Way.

Fraser: So now we know our place in the Milky Way. And… surprise, surprise… it's not the center of the Milky Way.

Pamela: Right, right.

Fraser: So, what was next?

Pamela: Well, now we're in an age of just filling in pieces. And that's a nice, comfortable place to be. We know where we are, we know where we are in the Milky Way, we know where we are roughly in the universe… which is just somewhere… everything is the same everywhere… it's all expanding. In 1930 Clyde Tombaugh discovered Pluto, growing our solar system a little bit more… expanding the walls and filling in the details.

Fraser: Poor Pluto.

Pamela: Yeah. Well… Ceres had the same fate and no one ever says, "Poor Ceres."

Fraser: Poor Ceres… That's true. Planeted… unplaneted… dwarf planeted.

Pamela: Right.

Fraser: Same as Pluto… right. Poor Ceres. We should do that. We should really pay our respects to Ceres. And, you know, it was important because it pushed out our observations and found a very large object in the Kuiper Belt, and began the discovery of many more objects in the Kuiper Belt. And at the time… oh we got a new planet… but as the observations came in, it kept getting smaller and smaller and more like everything else in that region.

Pamela: Right. Well, they didn't know that there was other stuff in the region at the time. That's the interesting thing, and that's part of why it got to stay a planet is they knew almost immediately that this sucker was tiny and not like Uranus or Neptune and not at all like what they were expecting. But, they wanted a new planet, so dang it… it was going to be a new planet.

Fraser: Right, but also I think it was the methodology that was used to discover that was quite… I don't know if it was revolutionary… but very efficient. I mean they used these photographic plates and they switched them back and forth, and that's a method that's still used now to find asteroids and comets and Kuiper Belt objects… to go at it in such a systematic way really proved a gold mine for finding new objects out there. It's almost like finding Pluto was part of it, but also just… and I'm sure you turn up all kinds of other stuff by having a really powerful way of seeking objects in the sky.

Pamela: Right, so there were asteroids, there were novae, there were variable stars. But, it sure would have been nice if it could have been another Neptune-like discovery where it was just done mathematically… but that didn't quite work out.

Fraser: Who's next?

Pamela: So next is… well, now we start adding colors of light. We have Karl Jansky discovering that radio waves come from the sky just as much as they come from, well, radio transmitters. So he was the first person to realize that if you look upwards, you can start getting signals. Jupiter is an easy culprit. You can detect Jupiter with a good ham radio, if you want to.

Fraser: And I guess fortunately, the earth's atmosphere doesn't block radio waves.

Pamela: Not most of them… and so that made it easy. So we have Jansky filling out the radio spectrum. Then we start finding stuff that's invisible. We had Zwicky in '33 was looking at clusters of galaxies and realized that they're moving faster than they should. The orbits within the clusters aren't what they should be, and he put forward the idea of dark matter and no one listened to him… nobody listened to him at all.

Fraser: People aren't entirely listening to him today, still…

Pamela: Well, no… that's true.

Fraser: Yeah, you still get a lot of people that still don't like that dark matter idea…

Pamela: Well, and beyond that, Zwicky is the first case of… if you're a cranky person, no one listens to you. Zwicky is famous for being a cranky person at Cal Tech and traumatized many generations of graduate students. So, if you're going to discover something, be non-cranky and don't be a crank. Two different rules, but both apply.

Fraser: But this was one of those mysteries that was opened up back in the 30s, and we're still waiting to close it up now. We're getting tantalizingly close with a lot of the evidence that's been brought back by Hubble, but we're still not there yet. We still can't definitively say what it is.

Pamela: And the thing is, so at least we've gone from Zwicky saying something weird is going on… things are moving too fast… these galaxies should be escaping… they surpass the gravitational binding energy… to… skipping ahead, we'll go back… in the '70s we had Vera Rubin looking at galaxies and finding that the orbits within galaxies made no sense… to… there was a long period–decades-long period–of people not knowing if it was a problem with our understanding of gravity or if there was just stuff that we couldn't see. Now we can say with confidence that the majority of dark matter is nonbaryonic matter that doesn't interact via the electromagnetic force and is collisionless for all intents and purposes. And while most of those words don't make sense without many years of physics, that's much better than "there's stuff out there." And that's where we started.

Fraser: Yeah, small stuff that we can't see… that doesn't bump into each other. What was next?

Pamela: So this is going to be the point, point, point type of …

Fraser: Yeah, I like when we can tell these kind of weaving narratives, but in this case it's just like… discovery after discovery…

Pamela: There's so much stuff…

Fraser: Like, oh yeah, you know… pulsars… quasars…

Pamela: So according to the timelines I've found, nothing interesting happened in the '40s. I think this probably has a lot more to do with the fact that there was a world war going on, and most energies were put into other things, unfortunately.

Fraser: But there was some work in rocketry, right? There was the V-2 rockets…

Pamela: Right.

Fraser: So, not necessarily astronomy, but some of the space flight…

Pamela: Right, so we can go back and we can look at… in 1926 there was Robert Goddard who started using liquid-fuel rockets. And the nice thing about liquid fuel is that you can turn your engine off. If you have a solid rocket booster, once she's fired… it just keeps going. With Goddard's invention of the liquid-fueled rocket, it changed how we can build rockets and made steering a lot easier as well. And Werner Von Braun in Germany continued this work and then carried it over to America when we ruthlessly stole him. And in the 1950s, this brings us into the space age where in '57 Sputnik was launched…

Fraser: Beep… beep…

Pamela: Yeah, fully detectable. If you haven't seen the movie October Skies go watch it, or read Rocket Boys. It's a fabulous story. And in America… not to be competitive or anything… in 1958 had to launch their own rocket, the Explorer I satellite went into orbit. Suddenly, new things were possible. We were able to start thinking about the idea of space telescopes, and as soon as we had satellites that was one of the first things that astronomers started dreaming of was space telescopes.

Fraser: So, what about… I mean there was one big question that still hadn't quite gotten answered yet, which was like "where did the universe come from?" Or, the shape and expansion of the big bang… so where did that come from?

Pamela: Well, so big bang is one of those things that… it actually is a rather derisive term that Fred Hoyle came up with in a 1949 radio broadcast. He is one of those people who is both amazingly brilliant and also wrong periodically. So while Fred Hoyle has done many, many amazing things, he's also the person who warned that maybe landing on the moon wasn't such a good idea because maybe the dust was so deep it would eat the spacecraft. He really, really didn't like the big bang. He preferred the idea that we live in a universe where every cubic meter of space just sort of magically has stuff come into it… this is a steady-state model and it turns out to be wrong. So in a 1949 radio broadcast, people were debating is this right, is this wrong… it was Fred Hoyle that said the big bang is hooey… basically. So that was when they started debating the existence… then we had problems like the cosmic microwave background radiation getting discovered. So here in 1964… Penzias and Wilson… they're working at Bell Labs… there's noise in their horn… they can't figure out what the noise is… they scrub it, they check the electronics… we did a whole show on this–go listen to the show. And they find this strange hum that is the universe. This was finally the lynchpin that ended decades of debate about what is it that's causing our universe to accelerate, well not accelerate but expand. But throughout the '30s, '40s, '50s, all the way up until their discovery in '64. All we knew was that our universe was expanding… we can't point to any key moment and say that… that's the moment that we understood the big bang. We have to wait for the observations and the technology in the '60s.

Fraser: Right, and then inflation didn't come around until the '70s?

Pamela: So inflation didn't actually come out until the '80s. This is the type of thing where we were old enough to be reading when these ideas originated. And the problem with inflation is as we got better… well, the problem that was solved by inflation is Penzias and Wilson made their observations of the cosmic microwave background but their detectors weren't great. And as our technology got better and better, and as we better figured out that the cosmic microwave background isn't just in all directions and fairly uniform… it's in all directions and very, very uniform. And the only way to get that extremely uniform background is if somehow there is this epic of rapid inflation that stretched everything out and hid the lumpy, bumpy parts… like stretching out Silly Putty and destroying a comic that you've picked up on the Silly Putty. Or that stretched things out from a point where once upon a time they were able to communicate with one another… they were thoroughly mixed at some point in the past. So in 1980, Allen Guth came up with the idea of inflation and people have been working throughout the '80s and '90s and even today to try to figure out what could inflation be? What could have triggered it… what are the different ways that it might have been caused to end? It's an ongoing problem. Here we live in the point where we're filling in details, and that's hard and it's hard to look for key moments in theory in the same way you look for key moments in observation.

Fraser: Yeah, and key people, right? You know, we talked a bit about the space age… I'm sorry, we're going to be jumping around… I hate to do this, but there's so many trails to follow… and with Sputnik going up… but that's when planetary astronomy… and in many cases deep sky astronomy really got going. There were missions sent to the moon, missions sent to other planets…

Pamela: Right, so we had in the '60s the first successful landing in '66 of the Luna probe and Surveyor I by the USA, and in '69 we had Armstrong and Aldrin walking on the moon. Then in the '70s it was Venus, and Jupiter has Pioneer missions sent towards it. We're exploring Mercury with the Mariner probes, and Mars with Viking, and all of these different missions… the Voyagers get sent out and in the early '80s start sending back pictures from the gas giants. All of these different missions… they made it possible to see planetary surfaces as more than just fuzzy blurs. This was particularly important with Mars where we were finally able to squash the stories of there being canals and potentially life… It was a bit depressing up until we actually got things orbiting Mars. Well, we could see from Earth that the poles got bigger and smaller, we could see the dust storms, you could still hope that maybe there was vegetation, that maybe there was life… and if you read old sci-fi you can suddenly see… well, the Mariner missions got there and the sci-fi community changed because Martians no longer played a role in sci-fi.

Fraser: And Venus was no longer a wet world… it changed to a hellscape.

Pamela: It was an acid planet…

Fraser: But they landed… in the 1970s they landed spacecraft on the surface of Venus and sent back pictures of the surface of Venus. They landed the Viking probes on Mars and sent back pictures. So, we're just getting back images from the surfaces of other worlds. There's nothing like getting up close and taking a good look to build your scientific knowledge, and that really is what a lot of the last half… even the last few decades of the 20th century was just dominated by all these planetary discoveries.

Pamela: And we're still continuing to make them. Just this week there's further understanding of Saturn's moon Titan and its atmosphere and the abundances of chemicals in that atmosphere that are pretty odd and leading to some really interesting questions about… is there some new chemistry that we're still trying to understand on Titan. Or more interestingly, is there maybe methanogen-based life on Titan. Mars… we're finally proving there was water on Mars… and we're finding water on the moon… admittedly not in useful form… it's embedded in the geology and you'd have to tear apart rocks to get at it. But still… that's cool.

Fraser: In 1990, probably the most important scientific instrument ever made…

Pamela: Hubble launched with bad vision…

Fraser: With bad vision, and was fixed in a few years… and then maybe the last great discovery of the 20th century… in 1998…

Pamela: In 1998 was the discovery of dark energy by two different supernova teams… And that in itself is just sort of the final piece of changing our perspective to the modern perspective where we know the universe is accelerating apart. And what's amazing, though, is even today we're still filling in details. When I was an undergraduate, we hadn't yet with certainty detected any black holes, and black holes were first theorized back in the late '30s and we're only now starting to say with certainty… yes, that system contains a black hole. It was only in the mid-90s that we were able to say that galaxies had black holes in the center and that quasars and active galactic nuclei and Seyfert 1s and Seyfert 2s and blazars… they're all the exact same thing.

Fraser: The discovery of extra-solar planets…

Pamela: Yeah….

Fraser: First around pulsars in the '90s… in the early 90s… and then around… and then mega-Jupiters orbiting other stars at the end of the '90s. But now we have 100s of planets under our belt, and more every month. Some are narrowing in towards Earths and Earth-sized planets. It's quite amazing.

Pamela: And it's one of these things where I have to keep throwing out books. Or at least throwing them into storage. Our picture of the universe is changing very rapidly, but how it changes is I think in some ways is more interesting. If you look at our past 4 episodes, the "how our understanding has changed" has almost consistently been driven by technology… Galileo gets the telescope and we're able to see phases of Venus that forced the sun out of the orbital place it had been and put it into the center of the solar system. We get really good recordkeeping by the Babylonians and it's possible to start to understand the eclipse cycle. You get instruments that Tycho Brahe and observers in the Persian empire used to very carefully plot out the positions of the stars and suddenly you're able to see… oh, our planetary models don't work… we need better planetary models. It was consistently observation technology forcing us to change our perspective. We now live in a time where instead it's filling in the details of the theory. And in some cases, our observations are ahead of us… we don't know what this dark energy stuff is… dark matter–we're halfway there, but we're not all of the way there. So now our theory needs to catch up with our understanding from observational astronomy. And that's a really awesome thing.

Fraser: One thing that's quite neat to do is to go watch Cosmos again… and you'll see there'll be artists' rendering of things… like… oh, I wish we could see what this would look like… Well, now we know. Even quasars… he described quasars and wasn't quite sure what they were yet… and now we know. So, it's quite interesting to see… and Cosmos came out in the late '70s… early '80s… so even stuff that's maybe 30 years ago… big chunks of it are out of date, so it's quite interesting to watch… and yet it's still fantastic! I mean you watch Cosmos and it's amazing! Interesting to see how things are changing even from then to now. And it's all available on You Tube… you can find all the Cosmos episodes on You Tube. I've recently been watching them with the kids, and they're bored… but I just love it. Yep… planetary nebulae… supernovae… so, there's so many things that have just come out within this last century. But now, we've kind of caught up to now… and so the next episode we thought we'd look forward and talk about some big missions that are coming up… and some lines in science, some theories that the technology, we're hoping, is going to fill in all the holes. What are some of the big discoveries that might be made in the next 50 to 100 years? So, stay tuned for that and we'll talk to you next week, Pamela.

Pamela: Sounds great Fraser. I'll talk to you later.

Transcript: History of Astronomy, Part 4 – The Beginning of Modern Astronomy

Download the transcript

Fraser: Astronomy Cast Episode 186 for Monday April 19, 2010, History of Astronomy, Part 4 – The Beginning of Modern Astronomy. Welcome to Astronomy Cast, our weekly facts-based journey through the cosmos, where we help you understand not only what we know, but how we know what we know. My name is Fraser Cain, I'm the publisher of Universe Today, and with me is Dr. Pamela Gay, a professor at Southern Illinois University Edwardsville. Hi Pamela, how're you doing?

Pamela: I'm doing well, Fraser. How are you doing?

Fraser: Very well. Freezing cold, though. It's unseasonably cold here in Canada.

Pamela: That's not good…

Fraser: I know… surprise, surprise… but, yeah, so this week we continue our history tour. So, with our proper place in the universe worked out, and some powerful telescopes to probe the cosmos, astronomers started making some real progress. The next few hundred years was a time of constant refinement, with astronomers discovering new planets, new moons, asteroids, and developing new theories in astronomy and physics. Alright, so I think when last we left our heroes, we'd gotten to Newton, who, apart from being interested in optics, materials, and physics, and developed Calculus… he also did a lot of contributions to astronomy… specifically his theories on gravity. So he was able to help explain why planets and moons took the paths that they did around the sun and the planets. So, that contribution was pretty important. So where do we go from there?

Pamela: Well, the next place is… who did something cool with gravity? Now that we have this great theory, we can start playing… and it was Edmund Halley who was the first person to find a really neat application to the theory of gravity.

Fraser: I think I can guess what it was.

Pamela: You probably can…. the entire audience probably already has…

Fraser: Edmund Halley… what did he do? Yeah…

Pamela: So, he went through the records and started looking at comet apparitions. Up until the late 1500s, everyone had thought that comets were just atmospheric disturbances, but Tycho Brahe, as we've discussed before, figured out using parallax that comets had to be further away than the moon. Halley took it one step further and he started looking for regular appearances and found this one visual object that appeared on a fairly regular basis that seemed to vary between about 75 and 76 years and he ran all the calculations… figured out the effects of Jupiter, figured out the effects of Saturn… and made a prediction of when this comet, this recurring object, should appear one more time. Now he did this in 1705, and unfortunately he didn't quite live long enough to see it. In 1758 Johann Palitzsch observed Halley's comet based on those observations. It was thoroughly proven… gravity works! And you can do cool stuff with it if you bother to take into effect the gravitational yanks and tugs of the outer planets.

Fraser: So they could accurately predict every time a harbinger of doom would come through the night sky.

Pamela: And it's much less scary when you know when the bright shinys are coming…

Fraser: To harbinge the doom… um… ok, so that's great… and then I guess from that point other comets were discovered and tracked and predicted. I mean now, we know thousands of them, right?

Pamela: Right, and, unfortunately though, what we find is that most of these comets don't actually come back. What was pretty amazing about Halley's comet is it's really the only one of its particular orbital species that comes back on a regular basis and is visible naked-eye every time.

Fraser: Right… puts on a good show every time.

Pamela: Right. Most comets don't do that. Most comets that we see actually have a tendency to be rather suicidal when it comes to getting too close to the sun. So there's lots of objects that come in and we see them once and they shoot back out… or they plunge to their death in the sun. Still, comets are cool.

Fraser: So, 1758 was when Halley's comet was observed… what next?

Pamela: So now we start getting into the age of finding faint stuff in the sky. The things that are at the edge of your vision and you're not necessarily going to notice unless you're a very careful map-making observer.

Fraser: We have telescopes…

Pamela: We have telescopes… telescopes are cool! And with telescopes you can start to make accurate measurements of separations between objects… you can start to map the sky more effectively. And there were permanent observatories being built, and you really need to attach your instruments to the ground if you want to be able to make accurate measurements of where things are. Hand-made instruments–those lead to hand-made errors. So what we have now is we have Herschel building telescopes in England. He discovered the planet Uranus in 1781. We have Piazzi who's making his observations in Italy, and in 1801 while building maps he discovered the asteroid Cerus that was for a brief period of time considered to be…

Fraser: A planet…

Pamela: Yeah…

Fraser: The planet Ceres, yeah…

Pamela: And then we discovered other things occupied its orbit… kind of like what happened to Pluto but on a much shorter time period.

Fraser: Right, and Messier was working in France around this time, right?

Pamela: Right, and he was not discovering new solar system objects as much… he was looking for comets. He was compiling catalogs of them, but in the process of trying to discover comets… he kept finding these annoying non-moving, non-cometary faint fuzzy blobs in the sky. Now it turns out that these things that kept annoying him because they weren't comets, they turned out to be star-forming regions, nebulae, supernovae remnants, galaxies… and they didn't even have the concept of galaxy back in 1781. So, Halley made his comet, we had Herschel with Uranus, Messier with his faint, fuzzy object catalog, which, as a small child, I thought was the "messier" catalog of objects in the sky… which made perfect sense.

Fraser: Somewhere there's a cleaner one, yeah…

Pamela: Right…

Fraser: Now, we went into great detail on Herschel… so if you want to sort of hear more about that story, we have a whole episode just on Herschel. And a whole episode on Uranus… but… ok, alright… moving on… I guess after Uranus, then Neptune had to be picked up?

Pamela: Neptune came in 1846. This one was a little bit harder… actually it was a lot harder. They were trying to figure out how to mathematically justify Uranus' not-quite-right oribit, so there're a bunch of mathematicians… specifically Joseph Le Verrier and John Couch Adams who were trying to predict exactly where this mysterious Uranus-orbit-deforming planet should be located. And it was Levier who eventually got it right, and he gave his predicted location to Johann Galle and he went out and from his German observatory found Neptune. That brought us to our modern set of planets… the complete set was discovered by 1846. This was also the period where we were starting to get more physics concepts involved in science, as well. So we're completing our catalog of the solar system, and starting to dive into the details.

Fraser: Details such as…

Pamela: Well, there's the Doppler effect, which we kind of need to figure out where galaxies are… that was sorted out in 1842. Samuel Heinrich Schwabe figured out the sunspot cycle. He spent about 17 years observing the sun, counting the sunspots, and noticed that the numbers changed over time, so he started digging through historic records and was able to go all the way back to the 1500s. In going over all of these records, he figured out that there's roughly an 11-year cycle to where sunspots appear on the sun and the number of them that appear on the sun. So, suddenly our sun is not just a non-perfect sphere, it's a non-perfect sphere that shows its own seasonal cycles.

Fraser: Right. And next…

Pamela: And next… well this is where we start getting into astrophysics becoming its own science. In the 1860s we started as a field figuring out spectroscopy… splitting light through prisms and grisms and slits and looking for individual dark and overly bright spots in the distribution of light coming off of stars, trying to match those bright and dark lines with the fingerprints of chemicals that were in general set on fire in different laboratories. So what we had was Henry Draper in 1872 took the first photographic spectrum of the star Vega. This followed on the footsteps of Sir William Huggins working in England doing spectral analysis of stars. So between these two men we were able to start saying stars have a specific chemical compositions. We know what stars are made of… and that's a pretty amazing thing to start looking at.

Fraser: So were scientists or astronomers pretty convinced at this point that the sun was just a star? I mean had this been going on for quite a while now?

Pamela: Well, we suspected for a long time that our sun was like the other bright spots in the sky. It was with stellar spectroscopy that we started to be able to say our sun has the same chemical properties as these other bright things in the sky.

Fraser: Right, so you could even now look at other stars and go… our sun is kinda like that one. Right?

Pamela: Yeah… And that was the cool new part of this. And what's interesting about this point is… our technology still wasn't that great. Our telescopes were good, but the human eye was still involved, to a large part. So, we had folks looking at the moon and seeing canals and imagining aliens there. So this was still a time of discovering things. We had in 1877 Asaph Hall discovered Phobos and Deimos orbiting Mars and we were desperately trying to figure out… are there aliens on Mars by looking at the changes of the coloring on its surface. There were observations of the sun coming from Mount Wilson. We realized that our sun was alive, but we still didn't have the physics. We're getting there, but questions as simple as what makes the sun go… we couldn't answer.

Fraser: And I think it's interesting is that we're now a little over a hundred years ago… and we didn't know that the Milky Way is just one galaxy, and the other nebulae that we see could be other galaxies… don't know why the sun does what it does. Don't really know where the solar system came from and where it's going to go… don't even really understand what small pieces of matter… what things are made up of….

Pamela: The thing that really put it into perspective for me was… I've had the chance to talk to some very senior, in terms of age, astronomers over the years. One of my favorite things to do is ask what's the most amazing scientific discovery you've seen in your lifetime? And all of them have answered "galaxies." Just the fact that there are people alive who remember when we didn't know what galaxies were…. that's the thing that floors me on a regular basis. For people my age, the in our lifetime is probably going to be dark energy…

Fraser: Dark energy… or quasars as supermassive black holes…

Pamela: See, that one doesn't even really strike me as that amazing because the concept of black holes have been around for a long time and as far back as I can remember people labeled quasars as "the monster inside of the center of the black hole," usually with an amusing hand-drawn diagram. But then they said, it's probably a black hole.

Fraser: Right, but wasn't 1998 — it came out of nowhere. Oh, by the way, almost everything in the universe is this dark energy…. it's accelerating the expansion… yeah, yeah… so that's pretty monumental. I've mentioned this story a few times, I think, that my dad had an old book…. a planisphere, and it was from the turn of the century… 1920s… and it had in it galaxies, but they were nebula. So, this is where the Andromeda nebula is…

Pamela: And you can still talk to some of the oldest astronomers at meetings and they'll say the Andromeda nebula because it's just so ingrained in their heads that yeah… it's a nebula…

Fraser: Old habits die hard…

Pamela: Right, and so what to me is most amazing is in the early 1900s we still didn't know how stars were powered… which really starts to put limits on the age of the universe because they were trying to figure out… well if it's coal and it's this big, how long will it take to burn up? Oh, that's not long enough. And so in trying to reconcile the geological history of how old we suspected the earth was, and how old we could make the sun last by powering it chemically, there was a real struggle going on because the sun just didn't seem big enough to have lasted long enough to explain the geological history. It was Eddington working in the 1920s that was actually able to look at the results coming from Hertzprung and Russell who were looking at the characteristics of stars and their spectra and the differences between giant and dwarf stars and the chemical properties and looking at all of these pieces and at the theories of gravity. Eddington said that stars are supported with radiation pressure. The light being generated inside of stars is what's holding them up and causing them not to collapse. And it's nuclear processes in the center of the star that are causing stars to live for millions and billions and in the case of little red dwarf stars trillions of years. So we've only known that for less than 100 years.

Fraser: That's another one of those ideas that… just imagine how that impacted people when they looked at the math and thought about the implications of it… Now, you jumped around a bit… I mean we just crossed into the 20th century and there was a pretty important guy right at the beginning of the 20th century…

Pamela: Albert Einstein working at the same time… while we had Eddington and Hertzprung and Russell and some of the other observers trying to understand stars, we had Albert Einstein starting his work in Germany trying to take a deeper look at gravity. It was in 1905 that he introduced his theory of special relativity and it was through special relativity that we started to get a clear cut understanding that the speed of light is the same no matter where you are. This has all sorts of different consequences. It's brought us to E = mc2 . Nuclear power was able to be developed because of Einstein's work. So Eddington definitely couldn't have done what he did without Einstein along the way. But it was all of these men contributing in so many different ways during this real new renaissance of astronomy during the early 1900s that allowed us to understand stars last a long time, gravity may be a geometric issue rather than anything else that we previously looked at it with in terms of pure mathematics… He abolished ether as something that fills all of space and time and carries waves… it was no longer needed. It was amazing work. And from there he went on to do the general theory of relativity. It was actually Eddington who mounted an expedition to go on and make the observations necessary to prove that Einstein's theories were right by observing a solar eclipse and looking to see how the sun's gravity bent–gravitationally bent–the light coming from distant stars coming from behind the sun.

Fraser: Now I know this is not directly related, but this also at the same time that you had the rise of quantum mechanics. You had Rutherford and Bohr probing the nature of the atom… and so all of that physics, all coming together at the same time as well.

Pamela: Maxwell's equations, blackbody theory…

Fraser: Yeah, so all of those really helped each other… you can see how interdependent all of these… physics and astronomy are all at the same time to answer some of these questions.

Pamela: This was the point where it went from astronomy to astrophysics. And it was actually Chandrasekhar while he was at the University of Chicago who took on editing the then new Astrophysics Journal where people sat down and worked mathematically to find things that we couldn't come up with any other way. One of the most interesting controversies of this period was Chandrasekhar was able to predict that white dwarfs should exist through the gravitational collapse of stars that are no longer undergoing nuclear reactions in the center and are roughly sun-sized stars. They, without the radiation pressure, collapse… become a special… what's called an electron-degenerate gas… are chemically made of the same stuff as the sun, but the way that stuff is supported is completely different. But then he took his theories a couple steps further and figured out neutron stars and black holes. Eddington felt that this was just nonsense and the two men spent most of their lives debating this and black holes weren't actually accepted until Eddington died and stopped deriding Chandrasekhar's work. But Eddington… the idea that you could mathematically suggest such a thing without empirical evidence as a starting point was just preposterous. Astrophysics opens the door to say well, if you have these conditions, then you should have these novel types of objects that may not exist locally, but if we look far enough we should find them out there among the stars.

Fraser: And so you gave us a little bit of a sneak preview there about the discovery of galaxies so you jumped around the history a bit there so why don't we kinda go back again and talk a bit about Cepheid variables because that's important leading up to Hubble.

Pamela: Right… during this period, all of these concepts are tangled together and everything is emerging all at once. Harper has this amazing plate stack collection of literally glass plates that were used to image the sky the way that film cameras are used to
image everyday objects. One set of the glass plates was observations one after another after another of globular clusters… packs of old stars gravitationally bound together that all the stars in each of these systems formed at once out of the same stuff at the same time… also plates of the Large and Small Magellanic Clouds… partner galaxies that can be seen in the southern hemisphere. Henrietta Swan Leavitt, while working at Harvard as basically a calculator, this was in the days before computers and they hired women to be their computers for them. Henrietta Levett was going through plates documenting the brightness of variable stars, stars that change in brightness in some cases from hour to hour in very noticeable ways. What she found is that for one type of pulsating variable stars Cepheid variable stars that change in brightness over the course of many days, their brightness was directly related to how long it took them to pulsate in a given system. If you took the stars and you looked at all the ones in the nearby system and all the ones in a further away system, you can actually use this relationship between brightness and period to figure out exactly how far away these systems were. This is now called the Leavitt relationship and it was called the period-luminosity relationship for decades. This was our first real way of figuring out the distances to objects that we couldn't figure out by using parallax. It opened the door to figure out… where are galaxies? This was one of the things that Hubble worked on as well as many others. He looked at some of the nearest galaxies, and Shapley did the same and there's a bunch of different people who did this, and realized that there's pulsating stars in galaxies, too. I can figure out where those galaxies are. Then they also started looking at the distance to things and the relationship between velocity and distance. Hubble in 1923 was able to show that galaxies exist outside of our Milky Way. Then he went on to show that the further a galaxy is away, the faster it's receding from us. And this meant that our universe is expanding and that completely changed everything. Einstein with his theories had set the universe still using the cosmological constant… the math allowed it to be expanding or contracting but philosophically, even the scientists said… no, static universe… everything steady state. And Hubble went… no, it's expanding. And that allowed the Big Bang theory to be figured out, eventually.

Fraser: Right… and I think we'll save that for the next show. So I think we've got one more episode of our history tour, where we'll get right up to the modern astronomy and cover some of the… the Big Bang, some of those other big ideas, right up to some of the latest stuff. So, we'll do that for next week. Alright, we'll talk to you later, Pamela.

Pamela: Ok, talk to you later. Bye-bye.