 So let's get started. So hello everyone and welcome to the August NASA Night Sky Network member webinar. We're hosting tonight's webinar as usual from the Astronomical Society of the Pacific in San Francisco, California. We're very excited to welcome our guest speaker, Dr. Eric Huff from NASA's Jet Propulsion Laboratory. Before we introduce Eric, here's Vivian White with just a couple of announcements. Hi, everybody. It's nice to see so many familiar faces and new faces too. I just wanted to remind those of you on the Night Sky Network who are joining us online that this, what is it? Friday, the first, is your last chance to upload your events for the annular eclipse on October 14. If you put those on the Night Sky Network website by the end of by September 1, then we will go ahead and send you a package of eclipse glasses, solar viewing glasses, and other things. So make sure to get that on the calendars. I think that's all I have. Kat, have you got anything else? So today, we have a small little giveaway that we're doing at the end of the talk. And it is our galaxy umbrella. So after you have concluded watching the lecture, we're going to go ahead and send you a little survey. And then we're going to pick five winners. Stick around. And I will show that to you later on. I would have to turn off my background here and find the thing. All right. For those of you on Zoom, you can find the chat window and the Q&A window at the bottom edge of the Zoom window on your desktop. Please feel free to greet each other in the chat window or to let us know if you're having any technical difficulties. You can also send us an email at nightskyinfo at astrosciety.org. If you have questions, please put those into the Q&A window. It really helps us to keep track of those and whether or not we've answered your question or not. So welcome again to the August NASA Night Sky Network webinar. This evening, we welcome Dr. Eric Huff to our webinar. Dr. Eric Huff was raised in Bullhead City, Arizona and followed an early passion for physics to college in Tucson in a PhD at UC Berkeley. He's done original work on a variety of topics ranging from observational cosmology to tidal modeling of surface features on Jovian moons. And he just told us earlier this evening that some of the best viewing that he had time on the Palomar telescope and some of the best viewing that they've ever had was right immediately after the hurricane Hillary came through a couple of weeks ago. And so it just really cleared out the atmosphere for them. So that must have been a delightful experience for them. Please welcome Dr. Eric Huff. Thank you, Brian. I'm gonna go ahead and get started to share my slides here. So I'm really excited to be able to share with you the recent progress and images from the Euclid space mission. This is a mission that went up on July 1st this year, but it's something that many of us in the community have been working on for almost two decades. So what I've got here on the opening slides is the public release images. I'm gonna spend a lot of time in this talk talking about why we want these and what these will ultimately connect to dark energy. So let's get started. So I think, so this is me, you know, as Brian said, I'm from Bullhead City, Arizona and I followed this circuitous path to my current job at the Jet Propulsion Laboratory as a staff scientist. And across the top of this, from Berkeley onwards, I had spent most of my time in science trying to figure out how to make the measurements that I will describe to you later accurate enough for us to draw real conclusions about the ultimate fate of the universe from them. So it's helpful to sort of think back to where this all started with Henry 11 and the discovery, you know, the expansion of the universe. And I suspect a lot of people in the audience are, you know, familiar with the circumstances surrounding that, but, you know, the Cepheid variables that let us first begin to measure the distances to nearby galaxies, right? And then, you know, the famous plot where people sort of notice the relationship between the distance and the recession velocity. And for a lot of people, I think it's not intuitive to think clearly about what the expansion of the universe means. So I'll start there and say, you know, imagine when we talk about the expanding universe, it's very, very easy to say, well, let's, you know, to think about the universe as expanding from a single point. But that's not really what we think is going on. You know, we imagine, you know, if you filled space with a set of little bullies or markers and said, we're gonna let space expand, what we're talking about is every single marker in that space getting farther away from every single other marker. So if you're standing, you know, in one spot here in the center, it would look to you like everything was expanding away from you. And if you think about the red dot as being measured at one time and the white dot is being measured at an earlier time, you know, then it looks like things are moving faster the farther away from where they are. And that's pretty much what we see with Hubble's law, right? But if we move to a different spot, say over here and say, you know, the universe is expanding, what would this observer see? They would also see the universe expanding away from them in every direction. This is the uniform constant expansion of space. And people spent decades and decades trying to measure this accurately, you know, and cosmology, right, sort of an infant field, you know, in the mid 20th century, sort of had three possible scenarios, you know, an open and closed universe, things that were essentially, where the geometry of the universe as a whole was dictated by its matter content. But it took until the 1990s before the measurements of the expansion of the universe got good enough to really distinguish between these two. So on a plot like this, you might see, you know, well, I should say first, you know, the best indicator we had for a very long time, especially in the 90s when these measurements first got good enough to really let us discover what we know now about cosmology. And we relied on standardizable objects, supernovae, where the brightness, the intrinsic absolute magnitude, the brightness of the supernovae is predictable from other features of it, you know, sort of looks sort of a bit like this. And when you put all as a supernova on a plot, you know, that were measured, and I think this is up until about 2012, and say, you know, as a function of the redshift, how faint do things get? This is sort of another way of measuring that relationship between distance and expansion velocity. The conclusion that you're inevitably led to is that the universe is neither open nor closed, you know, it's not slowing down, it's not gonna collapse back on itself, but it's been actually accelerating for about the last, you know, five to seven billion years. This got a few people a Nobel Prize in physics, but it raised some important questions, as you can imagine. So why did it raise some really deep and fundamental questions in physics? So I wanna talk a little bit about why and what that means. So probably I'm not gonna be too heavy on the equations here, but I think you guys are, you can handle this, you know, you might remember having learned in school Newton's law of gravitation, where the force between two bodies goes as the inverse square, that's R here, the distance between them. And intuitively, this makes sense. Everything in the universe, every force that we have the occasion to deal with in our daily life seems to get less influential as we get farther away from them, all right? Now, on large scales, the universe is dominated by gravity. It's the only force we think actually matters, you know, between galaxies and on cosmological scales. In order to get an accelerating universe, you have to change how gravity works. You have to introduce something that behaves like this, right? It's got to be repulsive at long range. And it's got to increase in strength of the distance. Now that's very, very weird when you think about it. Nothing else really in our macroscopic experience behaves anything like this, right? And the reason that we don't have, you know, if you don't see it, it wasn't discovered in the nineties that it's so hard to measure is that that coefficient in front of the R here is very, very, very tiny, right? The influence of whatever is causing the accelerated expansion of the universe is completely minuscule on solar system scales. But in this calculation once, and it turns out the Voyager spacecraft, which has been going, you know, leap on a trajectory out of the solar system since the 1970s, has probably moved an extra 10 microns, right? Roughly the width of the human hair over the course of its whole journey as a result of this repulsive force. So what this means is that if we want to measure anything about dark energy, we have to go to scales where this term here, where that R becomes large enough that we can actually see if this is how things behave. So people trying to study dark energy have to make maps of the universe on the largest scales possible because that's really the only place where we have any chance of detecting the effects of this stuff and trying to understand what it is. Now I've written a specific equation here with a linear R, and that's, you know, our ignorance of this is really profoundly bad. You know, we don't know if whatever is causing the universe to accelerate apart is a constant in space and time. You know, we put some limits on that. The big question we'd like to answer is, does it ever change? Right? These are the big questions motivating working in the field right now. And I should say also what I mean by universe here, actually. So here's the universe. And what I mean by that is that if you were to do a simulation of all the mass in the universe and follow how all the particles that make up galaxies, larger structures evolve over time and then ask what an observer would see if they looked out into the distant universe and took a cross-section to that. You might see something like this. This is from a physics simulation of the evolution of matter in the universe as we think it behaves. And you'll notice a couple of things about it. The first and most important thing to remember is that because, as you know, light travels at a finite speed, the things that are farther away from you you see as they were in the more distant past. So there's you. We put you at the center. And the very most distant thing you could see, and this is an amazing topic and something I wish I had time to cover, but it's not our focus for today. The most distant thing you can see is the light from the cause is the cosmic wave background, which is the afterglow of the big bang. From a physicist's perspective, that's fantastic because it tells us what the system we're studying here looked like at very early times. Because it's a snapshot of a different part of the universe, just a mere 300,000 years after the big bang. Now, if we were to look at, zoom in really, really, really far here, on the scale that I've plotted this, individual galaxies are far too small to see. This is where we see modern, late-time bright galaxies like the kinds of stuff you see from ground-based telescopes, your big NGC galaxies, right? That's the kind of thing you can spot from the ground. This region, roughly, is the area where dark energy starts to become an important contributor. It's inside this circle, the sphere enclosed in this area, which is a marker in time, that the universe really starts to speed up and the acceleration becomes important. So our task is to sort of look at the early times, look at the late times, see how things evolve, because we get to actually see snapshots of the universe over the course of its whole history and compare how that evolution works to our models for it. We propose a physical model for dark energy and we compare it to how that structure in this map changes over time. Now, if instead of zooming in on individual galaxies, you zoom in not quite all the way in this simulation, at late times here, close to the center where we are, in the recent past, you see structures that look kind of like this, really clumpy, right? Little galaxies would be sort of at the center of this thing where I say little galaxies, even very big galaxies would be small at the center of this structures, right? And you see if you look at this map that it gets smoother as you go away from the center and the stuff towards the very outer edge, it looks a little bit more like this snapshot here, right? So what's happening is that the initial conditions that we can see in the microwave background are very, very smooth, hardly any ripples or wrinkles at all. And because gravity is the only important force, gravity pulls things together and takes structure that's very smooth like this and gradually by pulling the heavy things closer together, turns it into structure that looks like this. That's, we just call the growth of structure over time. And if you can imagine, what we're doing with dark energy is maybe changing the strength of gravity, then you would expect that to change how quickly you'll go from something like this to something like this. So if we could measure that, perhaps we could actually say just what is going, whether dark energy is changing in time or not, right? The first order question that physicists really wanna ask. So the big problem here is that everything that I've shown you on this map, right? Every single particle in this map, in the simulation is dark matter. And here's another thing I don't have time to go into but most of the math that we would have to measure in order to understand dark energy is itself dark. It doesn't interact with light at all. So we're kind of stuck. We have this thing that we know how to make predictions for and we really know for how much structure is in this map as a function of time, we can make pretty exact predictions. But those predictions are mainly about how the dark matter is distributed in space. Seems like a hard problem, right? So when I say predictions, what I mean is this. So if I look at the texture of this map, I plot how rough it is going from the outer edge all the way in towards the center. And you had a measure for just how tiny it was. You would see that it looks kind of like this. It grows and grows with time. That's just the map become going from smooth here to rough towards the center. This is a quantity or it's analogous to a quantity that in physics terms we can make extremely precise physical predictions for. You tell me you have a model for dark energy, I can make a plot like this and show what it predicts. If we can just measure this clumpiness of the dark matter and how it changes over a cosmic time, we can actually really say something about what dark energy is. So it's a bit like this, right? It's a problem. So this is from another simulation where people have added simulated galaxies, which is the sort of little islands of golden light here into the ominous dark webbing, which is where we think the dark matter would be. Our task here is essentially by looking at where the galaxies here are to try and say something about where the dark structure is, right? That's the task. That's what we have to do to make progress on dark energy. So the way that we do this is with a thing called gravitational lensing. This is another image I suspect many of you have seen from some of the early release games web data. And it's one of the most powerful and beautiful examples of gravitational lensing that I'm aware. What's going on in the image on the right is there's a massive cluster of galaxies and this big white thing here is at the center of it. And the mass from that cluster of galaxies is changing the path that light from more distant things takes on its way to us. So light rays that leave a distant source here, as they pass by this massive cluster, they take a little bit of a different trajectory. And if you imagine how a bundle of light rays that starts as a circle would travel, as it goes through this little bend, it gets distorted. And an image that starts out looking like this will end up looking like this. And what you see over here with these arcs is exactly that effect. That's strong gravitational lensing. And it's one of the most direct ways that we have to probe dark matter. But the example that I'm showing you here from web is cheating. And the reason it's cheating is that this is about as strong as gravitational lensing gets. What I told you we wanted to do in the previous slide was to map the structure of all of the dark matter, not just a couple of special places in the universe. So if you look at not here towards the center but farther out where you can see these galaxies out here, if I just showed you an image of one of these guys out here on its own, you might say, well, that just looks like a galaxy and nothing special. But if you take in all of them, you see that there's a systematic tendency for all of them to be oriented kind of in a circle around the center of mass. That's more like something we call weak gravitational lensing. Weak just means it's not strong enough for you to see with your eyes, but it still contains information about where the mass is along the line of sight between us and different things in the universe. Schematically, if I took one of those simulations I showed you before and I put a bunch of galaxies behind a slice through it, this schematic, so the red stuff here is from the simulation, this schematic has sort of shown you how a distant galaxy would be distorted by the foreground large scale structure here. And if you stare at it for a couple of minutes, you can see that these ellipses tend to be stretched roughly along lines that follow the contours of the mass. What's cool about, so this effect is exaggerated, the real effect from large scale structure is really too small to see and I'll show you more of that in a second, but this is essentially showing us how we would go from measurements of the blue circles backwards to some statistical measurement of how the red stuff in this image is arranged. We could look at how things are distorted and use the knowledge that they tended to be distorted statistically at least along contours of foreground mass. But that's the game, if we can measure the ellipticities of distant background galaxies, we can actually build up the information we need to make a map of where dark matter is. Another way of thinking about it is that, what we're essentially doing when we do that is it's like looking through a thick piece of glass and seeing where the images on the other side seem to be distorted and then going backwards from that to statements about where the glass is thicker and where it's thinner. So that's the task. So this is a pretty realistic simulation of gravitational lensing and it's for a different telescope than you could, but it has a lot in common with the Euclid images. And I've zoomed in here. So this scale right here is about the finest detail you can take in with the naked eye or the naked human eye. All right? So if I took this simulated scene with stars and galaxies and I added to it a massive gravitational lens right there, okay? This is the region where you should look to see how large the normal effects of weak lensing by large scale structure are, right? And then I'm just gonna blink back and forth here. So pop left, you see some pretty strong effects kind of like the James Webb image, but on the bottom right, you have to stare really hard to see very tiny changes, okay? So what we've got to do, the task of cosmology is to find a way to measure this indirect effect, you know, accounting for the effects of the optics and the scene, trying to figure out from the colors of galaxies what is in front of what, trying to essentially build up from all of this imperfect information, a map of where the dark matter is in the universe so that we can understand dark matter. So that's the game. And the question is, and the question people started asking in the early 2000s is, what kind of telescope would you have to build to do this? All right? So here are some things that a telescope that could map dark matter in this way would have to do. You'd need absolutely superb image quality because the effects that you're looking for are very, very small and tiny distortions in your optics. If you're doing this in the ground, changes in the atmosphere from night to night, all of that can look like a gravitational lensing signal, these tiny effects that we're searching for. The other thing is that this is a statistical measurement. We wanna make a map of the large scale structure of as much of the universe as we can see. And that means we can't use Hubble and we can't use James Webb because the fields of view of those telescopes are tiny compared to the whole sky. So that's it. We need a good telescope that can take in a wide field of view with minimal optical distortions and produce exceptionally high quality images. And so that's Euclid. That's the motivation. The first idea is about how to do this were laid out in about 2006. And there are a few different projects pursuing this. People might be familiar with the Vera Rubin Telescope on the ground and NASA's Nancy Grace Roman Telescope which will be in space circa 2026 or 2027. But Euclid is gonna be our first go at this with a purpose built instrument. So here's what it looks like. We have a three mirror and a stigma. We have a carefully designed set of struts in the image pupil to try and minimize or make the PSF as easy to model as possible. And we have about a 1.2 meter mirror. So about half the size of Hubble. But all of this is designed to make the optical distortions as small and as uniform across the whole focal plane as they can possibly be. This on the left is about what the focal plane design looked like. So what's gonna happen is that the light from the sky in focus is gonna come into this dichro can be split into one channel that goes to an infrared detector over here and another channel that goes to an optical detector over here. And you've seen images and we'll look at images and both of those things. You know, the cameras here, there are about 600 megapixels and they're gonna produce about a hundred gigabytes of images every day. This telescope is not nearby. It's at what we call Lagrange point two. And so the plan was to essentially try and downlink a hundred gigabytes of data a day from the two European space agency ground stations in Spain and Argentina. And they have about four hours to do that. It's a bit of a challenge but the ground station teams have done a lot of optimization and creative work on data compression. And they think we can do it. And then this is the plan for where Euclid is gonna look. So there's a couple of things I want you to notice here. First of all, this is gonna take a while. It's a six year mission. And this color scheme has shown you how we're gonna build up survey area over the course of six years. The second thing I'd like you to notice is this graphic my colleague lead over here data marketing. So here is the field of view of webs near camp. Here's the full moon. And these two patches are the area of the Euclid visible and infrared. That's the visible on the left and infrared detectors on the right. This is really the big accomplishment, the major design goal of the telescope. Just delivering this kind of image quality over a wide enough field that we can actually do the entire, virtually the entire extra galactic sky. At the end of the day, we're gonna get about a billion measurements of those galaxy ellipticities from these images. Here are the instruments themselves and people are interested and an idea of sort of what how a final telescope looked like. The NISP instrument was built by my colleagues here at JPL. This is a big NASA JPL or a NASA JPL in European Space Agency collaboration both on the science and on the instrument side. And then here are some sort of cool shots of Euclid sort of during final assembly after the shake test on the left. Gives you a sense of sort of what the scale of the telescope is relative to a human being. There was a bit of a delay that was caused by the launch schedule, however. When this whole mission was originally planned, the idea was to go up on a Soyuz rocket and after the invasion of Ukraine that became impractical. And so ESA eventually contracted with NASA and SpaceX to launch it. And here's Euclid leaving from Italy for Cape Canaveral on April 14th. I was actually there at the launch on July 1st. SpaceX did a fantastic job of getting us exactly on target and performance verification started on schedule. This is sort of a cool shot from mega cam in Hawaii where someone actually spotted Euclid on its way out to L2. This is on July 12th. And if you want to know, here's actually what the first part of the orbit around Lagrange 2 looks like. So there's the Earth and here's the orbit of the moon. And this is a stable region sort of in space and in velocity, but it's not a single point or a small point is, you know, the actual orbit will be following as larger than the entire Earth in the system. It's about three times as far away from the Earth as the moon is. And so getting the data back, as I mentioned before, is a little bit of a challenge. So we've also had now that Euclid has been up our first science images from the instruments on board. And for the most part, things look fantastic. So this one panel here is four of the visible band detectors. And I've highlighted a couple of features that I think would be fun to look at, right? So here's a globular cluster. You can see the spikes of the PSF of Euclid here. We're spending really an enormous amount of time trying to model that to understand it because that's not just there in the stars, it is of course affecting the galaxies as well. What I'm showing you are the raw images. These still have a long way to go before they can be used for the science that we wanted to. So here's some examples of why. You know, you see all over this image the cosmic ray. These have to be sort of carefully removed by algorithm. And then here, for instance, is the image ghost from this bright star right there. There's still an enormous amount of processing but what these can be used for science but the basic performance of the telescope really in terms of the optical performance and the image quality is right what we were hoping for. Here's another one of the, this is an image from the infrared channel. So you can see the same PSF of the telescope and some of the more esoteric detector artifacts and other things going on. So cosmic rays in the infrared, that's maybe what you would have expected but there are some fun electronics artifacts that show up in the image. It's not unexpected, but things that still have to be removed from the data before we can actually do precision science with it. And then I haven't talked much about this but the other thing going on on the infrared channel is the spectrograph. So what's happening here is you're seeing an image very much like this one but with a dispersing element in the optical path. And so what that means is that for each star in galaxy here the spectrum of the light from that star is being dispersed vertically in the image. So here is the spectrum of a star and here is the spectrum of a galaxy and then there are electronics artifacts that again show up here and here. And one of the major data analysis challenges is to disentangle all of these overlapping spectra. Now, we will have data with these spectra taken at different angles and so there's enough differences between theme of the sky, different dispersion angles that we can disentangle but it's still going to be a major data processing challenge. And then I think the other thing that's probably we're saying here is that we've run into some problems as well. So one of the elements in the focal plane here is the fine guidance sensor which is relied on once the telescope has slewed to the correct position to provide precision pointing. And this has started to intermittently fail. So we halted performance verification, the point where we're looking at the science data and trying to sort of do a preliminary analysis on it to make sure that things work on August 25th. And the European Space Agency is currently working on temporary, it's developed a temporary solution to keep the telescope from losing its pointing. And they're very hopeful about being able to fix the software that's glitchy in the fine guidance sensor but that's the current data thing. So we've put science operations on hold for a bit and we'll resume once we can point to telescope. So I wanted to give people a little bit of a context for what a survey like this actually looks like. So what I'm going to do is stop sharing my screen and switch to a browser. Here's the URL I'm about to go to if you want to follow along. This is one of my favorite science, astronomical science tools. So what we're looking at here is data from some of the best, possibly the best wide field ground-based survey today. This is part of what's called the legacy surveys for another big dark energy project called the Dark Energy Spectroscopic Instrument. But this is ground-based data. You might expect the scene here to be about an arc second but it's still quite beautiful. And if we zoom out, right, you can sort of see groups that you might be familiar with but we're doing a survey. We want to cover as much of this guy as possible, right? So this is data that you could will be getting vastly improved versions of but we want to cover with that camera essentially all of this area. And we want to do it at a level of detail that is significantly superior to what we have here. So what did that actually look like? Let's talk about that. So I'm going to switch back to the slideshow. So this is a movie. I'm going to play that contrast data from the same survey I just showed you with new images from Euclid. So the different colors are just a result of the different overlapping images in different bands and different filters from the ground-based surveys I just mentioned, but here's the Euclid images. Same patches guy. And you can just see how much better the resolution is and how much deeper things are even through the cosmic rays in the dark. So a couple more shots of this. I just love staring at these things that kind of salivating about the data frankly. Just the level of detail and precision that we're going to have to work with here is astonishing. We'll do one more, I think. Is that globular? Okay. So, and all of that is essentially one single detector from the full focal point. So there's just going to be an enormous amount of imaging survey data here. And then I'm going to close here. So you can follow this as it's going on on the Euclid Consortium blog. You can see the first light images shots of the telescope as it's been constructed sort of keep up with news from the survey as it's going on. So I think the last thing I'll say here, I indicated this a little bit at the beginning, but dark energy was really first detected as an effect in the universe in 1997. The whole community got together sort of circa 2004 to 2006 to decide how we should begin to answer just the first order question. Does it change with time? Is it the same with time? Is it the same everywhere? Not answering the question of what is dark energy, but just answering the first questions you might want to have. And Euclid was essentially dreamt up in those early studies. So there's a vast community of scientists right now working in cosmology who have essentially been waiting for, not quite 20 years for this to show up on the scene. And in the next couple of years, we're going to have Nancy Grace Roman and Ruben as well. And this right now is going to be the golden age for modern cosmology. We have finally achieved a level of sensitivity and precision that should allow us to begin answering questions about dark energy. But the other wonderful thing about these surveys is that because they're designed to be so comprehensive, because the quality requirements on the images in the spectroscopy are so tight, we can't even begin to think about all the other things we're going to use these data for. And they will all be public. So I'm going to stop there. And I would be happy to sort of take questions and discuss the material. So thank you. Great. Well, thank you very much, Eric. And we do indeed have quite a few questions here in the Q&A. And so let's get right to them because we've got a lot of them. I want to come down to this one first off that was posed by one of the people. Why was the telescope named Euclid? That's a great question. So Euclid was a great mathematician, pioneer of geometry. And the basic questions about cosmology that I mentioned at the beginning is the universe expanding and how fast those things have implications for and are closely tied to the basic geometry of the universe. And what I mean by that is that, if you zoom out to very large scales, questions like are there 180 degrees in a triangle or not that you might remember from high school geometry, those things change depending on the geometry of the universe. So Euclid is Euclid in part because this is what it's hoping to try to measure. Kind of also related to the, I guess, where the telescope is. And so we have a few questions. I mean, they're going to lump them together as a, why is that out at Lagrange too? And not someplace else. So Euclid is at Lagrange too, mainly because we need low backgrounds, dark skies. And I think that's the principal part. This is a statistical measurement. We need to see as many galaxies as we possibly can. And so minimizing Earth's line was important for mission design. We have a couple other questions having to do with where it's located. And one says, unlike Webb, you don't have to stay in the Earth's shadow when you're out there. That's right. We're trying to do broad coverage of the whole sky. But as you saw from the orbit, the Lagrange orbit is so large that we really aren't going to be in Earth's shadow, like really for a significant portion of the time. Those orbits are vast. It's really more that they're stable. You can put something far from Earth and expect with very little expenditure of reaction mass to stay there for a long period of time. Now that's interesting too, because it has an infrared detector, like the Webb telescope is primarily infrared and there's a significant amount of shielding to keep it cool. Is there a similar amount of shielding on Euclid? No, no, not nearly as much. And the reason for that is that Webb is operating out to the far infrared. And so the detectors had to be cryogenically cool to a much colder temperature than Euclid's do. Euclid has a single channel operating in the near infrared. And it's also not trying to be as sensitive as Webb is. Webb is a huge telescope. It's got a small field, but it's designed for drilling deep, seeing very faint sources. We don't quite need to be as sensitive in the infrared as we do for Euclid. Great. So there are several questions about the difference you've alluded to both dark matter and dark energy. And so people are wondering about, how are we defining these? What's the difference between them? One person says they're distinctly different phenomena. Are they not? Indeed. So it's unfortunate. Astronomers, I think professional astronomers in particular have a bad track record when it comes to naming phenomena. So dark matter, we're very confident exists. We can map it out using gravitational lensing as I described, but also many other dynamical techniques. And it has a unique signature on the way matter behaves in the very early universe, involving the cosmic microwave background. But essentially what it is, it is some form of matter that interacts with gravity in a very ordinary way. And as far as we can tell in no other way through none of the other forces of physics or nature. So no chemistry, no electromagnetism, which means it doesn't interact with light. And we have not detected any evidence for a dark matter interacting directly with the other more subtle nuclear forces. But we know it's there and it has a significant impact on how things move in the universe and how things are gravitationally land in the universe. It's the best way to think about it is imagine a particle that just doesn't collide directly or interact directly with the other particles that your body and the world that you know is normally made up. Dark energy, you should think of as being a catch all term. We've seen that the universe is not only expanding but as I showed at the beginning of my slides, accelerating. And dark energy, I think it's most convenient to think of as being just the name for whatever it is that is causing that accelerated expansion. Right now we don't have any reason to think that the two are connected in any significant way. So really defining what both of them are is a very much an open question in cosmology and physics and we've got Nobel prizes on the line here. Yes, well, a few that have already been awarded. Maybe one way to say this and part of the reason that dark energy is a topic of such intense interest even though we've known about both phenomena for a long time is that particle physicists who like to dream up, you know, extensions to the standard model of how physics works can very easily invent new kinds of particles that are consistent with what we know that don't interact directly with chemistry or light. There are things in nature that we already know about that only very weakly interact like neutrinos. A lot of neutrinos have to pass through you before any one of them will interact even remotely. But dark energy, whatever it is, is so much more fundamentally strange that it's got to produce essentially it requires a significant revision and how we think the laws of nature operate, the forces themselves. We don't know exactly what that is, but, you know, we're unable to answer even the most elementary questions about it beyond just roughly how much of it there is. Kind of sticking with this idea of dark energy and dark matter. And so we do have a question here is so dark mass and presumably we're thinking matter, but maybe you could extend that to dark energy as well, is dark matter everywhere even within our solar system? Right, yes, absolutely it is. So because, so an important fact about normal matter is that, you know, when you look at the planets, right, orbiting in our solar system, the planets stay in their stable orbits. And the reason they stay in stable orbits around the sun is that in order to change the orbit, they have to lose energy somehow, right? Now the stars that we, you know, that we depend on for our energy and the planets, the way that they formed involved matter coalescing and collapsing, right? And it can do that because it can radiate energy away and collide with other particles, right? And what that means is that if I have another kind of particle, whatever dark matter is made of, that doesn't collide or interact with anything except gravity, it's mostly just gonna stay in large orbits more or less forever. And so when we make maps of where dark matter is, what we see is that galaxies are like little hard nuggets and they're sitting at the center of big diffuse clouds of dark matter. We call those dark matter halos. So it's everywhere, but it's not exactly distributed the same as luminous matter, for that reason. Okay. So we're still, you know, sticking with this idea, a lot of questions about dark energy and dark matter here. And so one person says, I've heard of dark energy being described as a property of space, but hadn't heard it presented as a feature of the gravitational force before. Is there a consensus on conceptualizing dark energy in this way as a feature of gravity? There's, so in the talk, it's useful to sort of try to careful to say this very specifically, it could be the case that the accelerated expansion of the universe is a result of gravity not behaving the way that we expect. It could also be the case that there's an exotic field in the universe, a feature of particle physics that we haven't yet discovered that also has that effect. What I was trying to illustrate is that no matter what model you introduce, it has to behave like a long range modification to gravity that is repulsive, even if it's not itself directly in modification to gravity. So you've got to have something that, you know, pushes things apart and gets stronger as they get farther apart in order to explain the accelerated expansion of the universe. I would say to just be really direct about this, we don't have a consensus about exactly what is causing this phenomenon. Could be a modification to gravity. It could be an exact new particle. It could be something else. So one person noted that, you know, that maybe this is similar to thinking about the ether that was fairly accepted back in the 19th century. And perhaps the real explanation is that would require some more foundational change to our understanding of physical reality to really be able to understand this. Is that an accurate? So, I would make a distinction there because the ether was a theoretical construct that people had postulated to explain some of the way that nature behaved. Here, all we have to work with is the empirical fact that the universe is accelerating apart. And dark energy is the catch-all term for whatever ultimately explains that, right? So unlike, you know, in early 20th century physics with the ether, you know, we don't have a consensus concept that needs to be overturned in order to explain this. We have models that fit the data, but there are many of them that fit the data and we're just not sure which one is correct. So this is an interesting, you know, thought experiment. And so is Andromeda moving towards the Milky Way because the attractive force of gravity is stronger than the repulsive force that dark energy is generating? Absolutely it is, yes. And if you work out, there is a significant but not overwhelming repulsive effect of dark energy between the Milky Way and Andromeda. If we could know exactly where the two galaxies started out and measure them and know their masses precisely, it might be possible to use their orbits as a probe of dark energy. But we really, the local group is too messy and we know too little about its detailed history for us to actually be able to use it in this way. But it is an effect that has a small but non-zero effect on the dynamics of things even at this range. And that actually kind of brings up another question too is about the time effect on this. And so we had one question saying, have dark matter and dark energy always existed in the universe from the beginning of time presumably since the Big Bang? Or do you hear later, have they evolved as well along with the universe? So if you think about how the dynamics had the expansion rate of the universe which is the thing that we can measure responds to its content. What people have worked out is that the main thing that's important is how, if you wanna say how does the universe change if I change the amount of matter in it or the amount of dark energy or the amount of radiation? The thing that's important about the substance from the universe's perspective is how its density changes as you stretch the universe out. And this might be a little counterintuitive because you might think, well, pretty much anything that there is if there's a finite amount of it, if I expand space, the density of it has to go down by the amount that I have expanded the space, right? I've got this many atoms in this much space, make the space bigger, the density goes down. But not everything works that way. So people here I think are probably pretty familiar at least in passing with the notion of the redshift of light, right? The energy of a photon changes as the color of light changes as light gets redshifted or bluechipped. And as the universe expands, space times expansion effectively stretches out the wavelength of light that's traveling through it. And so the density of energy that is in the form of light photons actually goes down faster as you expand the universe and the density of matter. So what that means is that if I wait and let the universe expand, given enough time, no matter how much radiation I start out with, eventually it will be less dense and thus less influential than ordinary matter, right? So the thing about dark energy, the thing that seems to be true at least approximately about it is that as space expands, the amount of it per unit space does not seem to change. And so if you wait long enough, even if there was dark energy in the very early universe, matter was much more dense because everything was closer together. And so even though it was there, it can't have had that much influence, we think. But if you wait long enough, the matter gets stretched out, dispersed over broader and broader regions of space as the universe expands, everything else does. And then all that's left in any given random patch of space is mostly dark energy. Great. Let's think a little bit about some of the imagery that is returning from that. And so we have a question about on one of the first slide images, you had that one image with all the elongated vertical lines on it and it's kind of become kind of that little iconic image of it. And so if you could maybe explain that again a little bit what are those vertical lines? Yeah. It might relate to what you were just talking about to some extent. Sure. Let me put this image back up and we can make sure we're talking about the same thing. So the vertical lines, are we talking about this image here? I think that one of the first ones where you have all those, the smeared out spectra, I think is what we're talking about. Yes, okay, okay, okay, cool, here. Yeah. Right, so what's going on here? Good. I didn't think I'd have time to explain this. It turns out that I did and I wish I'd put in a little more material, but essentially here's what's going on. I think probably most people are familiar with prisms. If I take a little piece of glass and I stick it in a beam of sunlight, I get a rainbow, right? And what's happened is that you've taken the white light which is the combination of all the light from the sun and you've spread it out so that each different wavelength of light ends up in a slightly different place leaving the prism. That's actually what's going on here. So it would be just as if I had a prism between the telescope and this detector and a sun beam coming in would be dispersed in this direction. So if you could see color, remember this is a camera and all it can count is how many photons hit it. But if you could see color, this might be red, orange, yellow, green, blue and so on, right, very roughly. And so each one of these things is just, just very much like what you would see if you took this scene or something like it and passed it through a prism. So from this star, you get a vertical rainbow somewhere. From this star, you get a vertical rainbow in a slightly different place. From this star, you get a vertical rainbow. So each one of those bars corresponds to one of the sources that you could see in a Euclid image but spread out like that. And the reason we do this is that because the universe is expanding and because light in an expanding universe gets stretched out the longer it travels to the universe, that means the redshift of the light is actually a pretty good proxy for how far away something is. It goes back to this distance redshift relation from the very early days with Hubble. Here's how far away something is and here's the velocity of it which you can measure with a redshift, right? So if we can, what we can do is we can use these spectra from Euclid, these dispersed rainbows of light from every single star in galaxies simultaneously in image to work out roughly how far away from us all of these stars in galaxy, all the galaxies in particular are because they're at cosmological distances. And what's cool about that is that it gives us a way of trying to build up a rough 3D map of the universe that Euclid will see. So not just the 2D that you see in the images but actually knowing what's closer and what's farther away. I think that's fascinating about how you can use that and you have to kind of look at it as a three-dimensional image. That's something that's difficult for us to kind of grasp when we're looking at this two-dimensional image and that would be really fascinating to see a plot on here and then to see just what the measured, I guess redshift is for each of these spectra. So somebody somewhere has probably done this. Yeah, so we haven't yet measured redshifts for these spectra because it's still early days and we haven't processed the data yet, but... That image was just taken, what, like two months ago, something like that, right? Or a month ago at most? In the last month, yeah. Okay. So kind of staying with that. And so we had the question of how long of exposure? Tell us a little bit about the exposure times, how we get the sense of when you do the Hubble Deep Fields that it was staring out there in space for X number of hours. How long does it take to build up this data to make one of these images on Euclid? So Euclid is gonna cover about 15,000 square degrees in about six years. There are gonna be a couple of fields that it visits many, many times repeatedly to build up a very deep image. But over most of the sky in each filter, it's gonna take four images and it's gonna get three of those spectroscopic images that like I showed you. So the exposure times, I don't recall off the top of my head, but they're going to be a couple of minutes, not a couple of hours. So this is what's necessary in order to reach the survey speed that gets us the entire sky over the duration of the mission. Okay. So kind of staying with that, what's the spectral response and the limits of the detector? How far into the infrared or are we looking? Right, so Euclid has, so the optical filter, and this I'm just gonna have to look up because I don't remember it. The optical filter stretches from sort of red wavelengths to sort of sort of into the near infrared. It's just got a single really wide band. And so the idea is that because we're trying to see fake sources, we kind of want something that's just a big light bucket, catch as many photons as possible. And then the near infrared camera is going to extend, let me just pull on my other Euclid talk here. Yeah, so the near infrared camera is not gonna go beyond, I think about two microns. So not very far into the infrared, partly because you wanna avoid the issues with having to cryogenically cool it to the temperatures of the web. Okay, so that kind of brings up another interesting question is that here we have this relatively narrow band that Euclid is imaging compared to some of the other telescopes, or at least it sounds like it's somewhat narrow. It doesn't go too far into the infrared. How does Euclid complement, and one person specifically called out DESI, but also some of the other telescopes that are out there, what's the potential for synergy with some of the other missions? So each of these things sees a little bit of a different window on the sky, right? So Euclid because, and it's not just that things, they see things in different wavelengths. So for example, Vera Rubin, which is another large imaging survey telescope, which is being built on the ground for similar goals, has a much larger primary mirror. It's going to be much more sensitive, but because it's looking through the atmosphere, the image quality will be significantly worse than Euclid's. So what we want to be able to do is take the very high quality, but shallower images from Euclid and compare them very directly to the images that Vera Rubin will take. So that lets us, you know, Rubin will see things that Euclid cannot, but Euclid will be able to tell us where Rubin is right and where it's wrong, you know, because of atmospheric distortions. That's an example of the kind of complementarity that we're interested in for surveys like this. So DESI, which I think mentioned, I was mentioned in the chat here, is the Dark Energy Spectroscopic Instrument. It's a ground-based instrument that's operating currently from Kip Peak in Arizona. And it's taking, like Euclid, many, many spectra of the sky, although over a different range. So Euclid will cover a somewhat different range of redshifts because it can see farther into the infrared than a ground-based telescope can. It can follow some of the emission line features that we are using to measure the redshifts to higher and higher redshifts, as they would be otherwise redshifted out of the window of light that we can see through our atmosphere. So that's another example of the kind of complementarity. And it's a generic feature of these kinds of things. You can build bigger things on the ground more cheaply, but you could reach into the infrared and get higher quality images from space. And that's the axis of love, which we try to complement these different, and design these different programs to complement each other. So there are a number of people including here in the Q&A that were curious about, you used the term ghost images and at least one of the slides. And so could you elaborate a little bit more about what you're meaning by ghost images? Absolutely, let me put the slides back up here. So, oh, this is the wrong slideshow. So when you look at, I'll go back to this image here. And we can zoom in a little bit like this. So this feature right here, this circle, right? What is that? So what's happened is that there's an optical path where light from this really bright start, because Euclid has a, like any reflecting telescope, well, like many reflecting telescopes, Euclid has a series of mirrors, in this case, it has three. And so you can get light that is, an image or something that's so bright that it reflects off of the detector, and the light sort of bounces back through the optical path, and some of it then comes back, right? And so you can end up with out-of-focus images of very bright objects in the field appearing in the wrong place. So this is essentially a very out-of-focus image of this bright star right here. And a little dot there in the center, it's just a coincidence. But that's what we mean by ghost images. So the faint, yep. I think that that works, but how did you figure out, how do you figure out that that is the image of that particular star? And, you know, that's understandable that you'd have these little artifacts in there, but then matching it up with the specific star that's creating the ghost image, that's mysterious to me, so. It's a little complex, but essentially, the thing about Euclid is because the measurements we're trying to make are so precise, an enormous amount of effort has been put in over a decade now of planning to anticipate and model all of the effects like the ones I'm describing here. So you can put an engineering model of Euclid into a computer. If I had a star at this angle to the entrance, where would the ghost of it appear? And you can trace the optical passes like a telescope, follow where things advance around and see where it would show up. So ghost images in particular, we anticipate and we model and we can effectively subtract them off. Okay. Ray diagrams. Yeah. Yes. We can understand that. All right, last question. And so we had a question about, you've had a really great opportunity to be working on the Euclid mission here. And a little bit about your hopes and dreams and what you're anticipating and what do you think you might get surprised by with the Euclid mission? So I think I'm really, really excited about the core science goals of Euclid. What is happening with dark energy? This has big implications if you think about it for the ultimate fate of the universe and the fundamental laws of physics. And I think if you ask many astronomers, maybe most of them would say probably just maybe out of theoretical prejudice or analogy to other things that dark energy is a constant in space and time and it doesn't change. And if you look at the literature right now, the preliminary measurements from smaller ground-based telescopes that are trying to do early versions, precursor versions of what Euclid will do, there's a little bit of tension between the data and that constant everywhere at all times model. Now, it could go away when we get better statistics but I'm kind of excited about the prospect of us finding the evolution of dark energy. That would be one of the most potentially very exciting outcomes. And that would represent a real deviation between how we think the universe works and how it actually works. So maybe you'll get to meet the king of Norway some years, so it's one of these years. I will not, but I suspect that someone from Euclid might be able to. All right. Well, thank you so much, Eric. This is absolutely fantastic. And so I think Vivian is gonna put a link to the survey in there. That's all for tonight. Thank you for joining us this evening. Thank you everyone for tuning in. You can find this webinar along with many others on the Night Sky Network YouTube channel. Join us for our next webinar on Tuesday, September 19th when Dr. Irwin Maserico will joins us to bring us up to date on the science of the missions to the Moon South Pole with a little bit more of an emphasis on the Artemis missions from NASA. So, but it's kind of exciting. There's an Indian probe up there now and everyone's trying to go there. And so we're gonna find out a little bit more about what's exciting about the Lunar South Pole next month. So keep looking up and we will see you next month. So good night, everyone. Good night. If you could just stay on for one more second, I wanna copy this in again and make sure that... Let's see. All right, there's a longer form right there.