 I'm going to talk for a few minutes about this paper that came out about a year ago now, which uses this technique known as the SETI ellipsoid. Before I jump into it, I want to make sure I highlight my many collaborators at the SETI Institute at Breakthrough and other places. It's a big sky with a lot of stars. And if you want to get the attention of another civilization like ours, you need to find some way to get our attention. You need to constrain parameter space about when you look and where you look and of course what you're looking for. There's a lot of debate in the literature about what to look for. We saw radio transmission plots we were looking for in the last talk. Here I want to talk about where and when. And there's this technique that has been introduced at least maybe even further back than the 1970s about using conspicuous astrophysical phenomenon that astronomers like us might be looking at. Using these conspicuous events that would gather our attention and piggybacking on those events or coordinating signals with those events so that we might already be looking in the right place to get our attention. Let me walk you through this technique. You have some noteworthy astronomical event, a NOVA, a super NOVA, some kind of title disruption event, something that plausibly an astronomer like you or I would be looking at and looking for. That event radiates out at the speed of light, the information about that event propagates out. That's the black circles here. And some extraterrestrial agent or civilization or something sees this event and then transmits its own signal saying, hey, did anybody else see that or hey, we're here. They're not at the same star. They may be light years and light years apart from the actual noteworthy event. They end up transmitting their signal. Now there's a time delay. They have to receive it. They have to see it. And then they transmit. Now here we are with our little radio telescope and say, oh, neat, a super NOVA or whatever thing we're looking for. We see the black curves first. We see that noteworthy event as well first. And then in some due course, we see the conspicuous secondary signal that comes from the other civilization. And this is some sort of signal coordination scheme that is plausible, which might be used to get the attention of astronomers like us. This triangle defines what we call the SETI ellipsoid. It's this ellipsoid that grows with time. With fixed foci, we are one foci. The noteworthy astronomical event is the other foci. And the other civilization or the other agent exists on the surface of this ellipsoid. And as light propagates out, as information propagates outwards, this ellipsoid grows with time. So it's a growing ellipsoid in time. And so this gives us a clear when and where to look. Stars that intersect these ellipsoids, these three-dimensional ellipsoids that are growing with time, stars that intersect them at given moments in time, are ones that we should look at. Gives us a very clear when and where to look. Less information about what to do, but there's a lot of literature about that. And of course, we're drawing triangles in three-dimensional space. The distance to things is the most important uncertainty here that we have to worry about in terms of defining the time. We need to think about what kind of event to look for. This is where anthropology comes in and you have to worry about what we're thinking and what you think the aliens might think and what they think you might think. But we're going to skip that for now. And we're going to focus primarily on supernova 1987a, which is sort of the best signaling event that happened near us. I like this two-scale figure. The steady ellipsoid is in blue two-scale with the actual sphere of information about supernova 1987a. You can see that the number of civilizations that could have transmitted something that we could have received have to be inside of that little blue ellipse. And it's very, very skinny, very narrow, whereas like the number of star systems which have observed the supernova is very large. Okay, I said distance is the big missing piece, the big secret here. And so this is where your friend in mind, Gaia, comes to play. Gaia is the best distance mission ever created. It measures the trigonometric parallax of stars, which gives us like a cosmic ruler that we can use to measure, with great precision, the distances of stars. And if you really want precise distances, which translate into precise timings, then you want to look at relatively nearby stars where our best measurement of distance is. And so here we're using the Gaia catalog of nearby stars, about 300,000 nearby stars with very good distance estimates. And so this Pokemon ball here is the Gaia supernova 1987a sediolipsoid. Stars in red are stars that have not even seen the supernova yet. Stars in blue are stars that have seen the supernova, but only ones in pink are ones that could have plausibly seen the supernova and then sent a transmission, sent a coordinated signal saying, we saw it too, notice us. And the little black dots are the ones at this moment in time when I made this plot of stars that are exactly intersecting that ellipsoid. And those are the ones that would be signal candidates. The takeaway here is that supernova 1987a, while it was a generation ago for astronomers, is still relatively new cosmic news. And so there's lots and lots and lots of stars that we need to monitor and we know when and where to look. And the ellipsoid grows at time and it grows and grows and grows. And it'll take more than a millennia to actually get all the stars in our neighborhood. So there's about 140 stars at any given moment in time. I'm gonna jump to the end here and say that there are more coordinated events besides supernova 1987a. There are galactic nova, there are tidal disruption events. This again, this is a matter of anthropology. You have to decide what seems important to you. But you can take these galactic nova and you can propagate them back in time. You can look at recent nova, you can go back in time and look at historic nova as well, going back 100 years, 1,000 years, even if you have historical supernova. The problem is with every one of these ellipsoids, you end up intersecting hundreds of stars and this adds up and this is where we need sky surveys. We've highlighted Gaia here. We've used this for its ability to monitor most of the sky over many years. But we are in the era of sky surveys, right? We are in the era of things like Tess and assassin. And soon the Rubin Observatory with its legacy survey space and time, which will monitor the entire southern sky with regularity. And so this is my call to action to you all, especially students. This is a great time to be getting into survey astronomy, into statistics. Of course, for all those bread and butter astronomy topics, but also into the study of technosignatures as they may be a way to discover life. And surveys I think are gonna play a key role. Thank you.